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Performance of spring-calving beef suckler cows and their progeny on four contrasting grassland management systems
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Livestock Science 117 (2008) 238 – 248 www.elsevier.com/locate/livsci
Performance of spring-calving beef suckler cows and their progeny on four contrasting grassland management systems M.J. Drennan ⁎, M. McGee Teagasc, Grange Beef Research Centre, Dunsany, Co. Meath, Ireland Received 16 April 2007; received in revised form 6 December 2007; accepted 11 December 2007
Abstract Data were collected over four consecutive years from four, rotationally grazed, grassland management systems each with 15 spring-calving beef suckler cows and their progeny to 13 months of age. The Systems were high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests — HH2; high SR, low N, 2 silage harvests — HL2; low SR, low N, 2 silage harvests — LL2, and low SR, low N, 1 silage harvest — LL1. High and low SR were 0.49 and 0.59 ha cow− 1 unit, respectively, and high and low N amounted to an annual input of 239 and 57 kg ha− 1 on the grazing areas, respectively. Where applicable, the four Systems received 114 and 80 kg of N ha− 1 for the first and second silage harvests, respectively. Equal areas of Systems HH2, HL2 and LL2 were conserved as silage (0.29 and 0.21 ha for first (24 May) and second (4 August) harvests, respectively cow− 1 unit) each year. Silage from System LL1 (0.37 ha cow− 1 unit) was conserved 14 days after the other first harvests. Following the final harvesting for silage within any System these areas of grassland were then grazed. During the winter all animals were housed and cows were offered grass silage and calves were offered silage plus 1 kg of concentrate per head daily. Good cow and calf performance at pasture were obtained at both high SR and high N or low SR and low N. At the high SR, increasing the level of fertiliser N application increased cow liveweight gain at pasture by 24 kg, improved body condition score (BCS) gain at pasture by 0.36 units and prolonged the grazing season by 7 days. Similarly, at the low level of fertiliser N, reducing the SR, increased cow liveweight gain at pasture by 21 kg, improved BCS gain at pasture by 0.23 units and prolonged the grazing season by 7 days. At the low SR all the winter silage requirements could be provided in one as opposed to two harvests thereby reducing the conservation area. However, delayed harvesting of silage resulted in lower silage digestibility and reduced calf performance in winter. The results indicate the specifications for a planned lower N grassland system, particularly where qualification for EU environmental schemes is dependent on moderate stocking densities. © 2007 Elsevier B.V. All rights reserved. Keywords: Beef suckler cow; Cattle; Grassland systems
1. Introduction
⁎ Corresponding author. Tel.: +353 46 9061100; fax: +353 46 9026154. E-mail address: [email protected] (M.J. Drennan). 1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2007.12.018
In many parts of Northern and Western Europe, current climatic conditions dictate that grass, either grazed or conserved, is the principal forage for beef cow and calf (suckler beef) production. Beef suckler cows are kept in a
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wide range of lowland nutritional environments, varying from high stocking rates (SR) and high inputs of nitrogenous (N) fertiliser to lower variable input systems with low SR, low inputs of N and potentially only one silage harvest. Many farmers will now need to operate to lower input criteria than heretofore, as determined by environmental legislation and (or) stipulated in environmental schemes such as the European Union (EU) Rural Environmental Protection Scheme (REPS). Due to an increasing environmental focus, the emphasis will be to restrict the application of N fertilisers and consequently, grassland management systems will reduce in intensity. Within the context of a grassland-based springcalving suckler beef production system, matching grass supply to animal requirements during the grazing season, while ensuring sufficient silage is produced for the indoor winter period, is largely achieved by balancing the use of fertiliser N and SR by altering the emphasis on harvesting grass by grazing or as silage. Thus, whereas harvesting grass for silage facilitates the concurrent and subsequent utilisation of grass by grazing (McGee, 2005), and the use of two silage harvests have traditionally been advocated for springcalving suckler beef production systems (Drennan, 1993), the considerable cost often associated with a second-harvest silage (O'Kiely et al., 1997) makes it necessary to consider replacing the two-harvest system with a simpler one-harvest system. There is very little information available on beef suckler cow grassland management systems, especially springcalving systems on rotationally grazed, temperate lowland pasture. This contrasts markedly with the number of studies published on spring-calving dairy cow grassland-based systems (e.g. Dillon et al., 2006). However, the nutritional requirements of the spring-calving dairy cow are much higher than the beef suckler cow and consequently, energy balance and performance of the dairy cow would be markedly different and more sensitive to changes in nutrient supply. Furthermore, the SR and fertiliser N inputs of dairy systems to date are generally much higher than beef systems. This makes it difficult to import results from grassland dairy systems to beef systems. The objectives of this study were to determine the effects of (1) reducing the application of fertiliser N to the grazing area, (2) allocating more land cow− 1 unit, and (3) reducing the number of silage harvests, on cow and calf performance on rotationally grazed, cow and calf-toyearling systems. The underlying hypothesis was that, compared to a high SR and high fertiliser N input (intensive system), reducing the input of fertiliser N would result in a reduction in individual animal performance, whereas using a low fertiliser N input combined with a
239
low SR would result in similar individual animal performance during the grazing season to the intensive system. Additionally, lower SR would permit adequate grass silage to be produced from one as opposed to two harvests thereby reducing costs. 2. Materials and methods The study was carried out at Teagasc, Grange Beef Research Centre (Longitude 6° 40' W; Latitude 53° 30' N; Elevation 92 m asl) over a period of 4 consecutive years (1992–1995), each year comprising a summer grazing period (April to October/November) and the subsequent indoor winter feeding period. The soil type was a moderately well drained Brown Earth of medium to high base content and of clay loam texture (Gardiner, 1962). Meteorological data were recorded at the recording station at Grange Research Centre. The instruments and standards used by Irish weather stations were described by Fitzgerald and Fitzgerald (2004). Grass production was measured in 1993, 1994 and 1995 in a separate plot experiment as described by O'Riordan (1997) involving a cutting regime to a 4 cm stubble height on a 4-week cycle using an annual fertiliser N input of 300 kg ha− 1. 2.1. Animals The animals used were spring-calving (commencing midFebruary) ≥ 7/8 Charolais cows, first-cross Hereford × Holstein–Friesian and Limousin × Holstein–Friesian cows, and their progeny. Each year the cows were bred using two Charolais sires, one by artificial insemination (A.I.) and the second by natural mating. Replacement heifers were bred to a Limousin bull (A.I.) to calve at 2 years of age and were introduced into the herd in Spring when animals were being turned out from the winter accommodation to commence grazing the grassland (i.e. turnout to grass). Average parity was 3.8 (s.d. 2.31) and calving date was 16 March (s.d. 21.4 days). The date on which grazing commenced in spring was dictated by a combination of grass supply, ground conditions and calving date, as all cows had calved prior to turnout. The average turnout date to grass for the cows and calves was 20 April (s.d. 7.5 days). 2.2. Grassland management systems The experimental area was a permanent grassland site comprising 32.5 ha. A total of 32 paddocks were grouped into 8 sets of four (balanced for location and soil type) and randomly assigned to four grazing management systems. The area assigned to the high and low SR systems was 7.36 and 8.88 ha, respectively. Average paddock size was 1.02 ha (ranged from 0.56 to 1.42 ha) and each paddock had its own water supply. For the two high SR systems, paddocks were of equal size within each set of four, whereas for the two low SR systems the area of four of the paddocks (the main grazing paddocks) was 1.5 that of the corresponding paddocks in the
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high SR systems. The paddocks assigned to grazing and silage harvesting were the same over the duration of the study. Each year at turnout to pasture, 60 cows and their progeny were blocked according to genotype, parity and calving date across four grazing management systems each with 15 cows and calves grazing together. The allocation of cows to the Systems did not take account of the treatments imposed in previous years (Wright et al., 1994; Drennan and McGee, 2004). The four Systems were: high SR, high N, 2 silage harvests — (HH2): high SR, low N, 2 silage harvests — (HL2); low SR, low N, 2 silage harvests — (LL2); and low SR, low N, 1 silage harvest — (LL1). High and low SR were 0.49 and 0.59 ha cow− 1 unit, respectively. A cow unit was defined as a cow plus progeny to 13 months of age. High and low chemical fertiliser N amounted to 239 and 57 kg ha− 1 annum− 1 on the grazing areas, respectively. In the spring, fertiliser N was applied to the grazing areas of all Systems at a rate of 57 kg ha− 1 in early March. No further fertiliser N was applied to the grazing area of Systems HL1, LL2 and LL1. System HH2 received additional applications after the first and second grazing at the rate of 57 kg N ha− 1 and two further applications of 34 kg N ha− 1 between then and 20 August. On the silage harvesting area, fertiliser N was applied at the rate of 114 and 80 kg N ha− 1 for first and second harvests, respectively. Following the final harvest of herbage for silage, 34 kg N ha− 1 was applied. For Systems HH2, HL2, LL2, and LL1 the total annual chemical fertiliser N application rate was 219, 146, 131 and 114 kg ha− 1, respectively. Urea (46% N) was generally used as the nitrogen source except in dry weather conditions when calcium ammonium nitrate (CAN; 27.5% N) was applied. Phosphorus (P) and potash (K) fertiliser application rates were based on soil test analyses (Gately, 1994). On the grazing area, a single annual application of 19 and 38 kg ha− 1 of P and K, respectively was applied in early Spring. On the silage harvesting area, the application rates of P and K were 21.5 and 92.5 kg ha− 1, respectively for both first and second silage harvests. After the single silage harvest in System LL1 an additional 18.5 and 37.5 kg ha− 1 was applied. Additional to the chemical fertiliser application, occasionally, slurry produced during the winter indoor feeding period was returned to the area harvested for silage in early Spring and again after silage harvesting at a rate proportional to the SR for the grassland management systems. The fertiliser nutrient value of the slurry was not determined. The swards consisted predominantly of perennial ryegrass (Lolium perenne) and were rotationally grazed. Botanical composition was not measured but visually there was very little white clover (Trifolium repens) present. Residency time in each paddock was the same for Systems HH2, HL2 and LL2, and was determined by visual assessment of the post-grazing grass height of System HL2, whereas animals in System LL1 were moved independently. The grazing management plan was such that all Systems completed each grazing cycle at the same time. Residency time per paddock (days) in Year 3 averaged 4.6 (s.d. 1.79) for Systems HH2, HL2 and LL2, and 6.7 (s.d. 2.13) for System LL1. Corresponding values in Year 4 were 4.3 (s.d. 2.32)
and 6.6 (s.d. 2.79) days. Equal areas of Systems HH2, HL2 and LL2 were conserved as silage (0.29 and 0.21 ha for first (24 May (s.d. 2.2 days)) and second (4 August (s.d. 5.8 days)) harvests, respectively cow− 1 unit) each year (Table 1). Silage from System LL1 (0.37 ha cow− 1 unit) was conserved 14 days after (7 June) the other first harvests. Grass was precision-chop harvested, usually with minimal wilting and with the addition of an acidbased additive when required and, ensiled in unroofed, horizontal clamps which were rolled thoroughly, before sheeting with 2 layers of polythene and covering with tyres. In the two-harvest systems the objective was to produce high nutritive value firstharvest grass silage for the weanling progeny and moderate nutritive value second-harvest silage for the cows. The cutting date of the second harvest was delayed to produce a higher yield, of lower digestibility silage (at a lower cost unit− 1 DM) as this is adequate for spring-calving beef suckler cows with relatively modest energy requirements for production (i.e. not lactating for most of the indoor winter period) (Drennan and McGee, 2004). Following the final harvest of herbage for silage, the subsequent regrowth was grazed in their respective systems. All calves were abruptly weaned in autumn at approximately 7 to 8 months of age. Weaning date for all Systems was determined by the grass supply in System HL2. Calves were removed from the pasture and housed indoors for the winter feeding period on 29, 7, 26 and 27 October in Years 1, 2, 3 and 4, respectively. Weaning coincided with housing indoors except for Year 4 when, due to poor grass growth relating to a soil moisture deficit, calves were weaned earlier than planned on 27 September and offered 1 kg day− 1 (following gradual introduction) of a barley-based concentrate supplement at pasture until housing time. After weaning, cows remained grazing at pasture until housing indoors, which was determined by grass supply and ground conditions. The average date of housing over the four years was 25, 18, 25 and 27 November for Systems HH2, HL2, LL2 and LL1, respectively. Herbage surplus to requirements on the grazing areas in Year 1 (late May/early June) and Year 2 (early May) was removed using equal numbers of yearling heifers grazing on each System equivalent to 25 and 204 yearling grazing days per System for Years 1 and 2, respectively. During the winter indoor feeding period the cows were offered grass silage (generally restricted pre-calving and ad libitum post-calving) and a mineral vitamin supplement (60 g cow− 1 day− 1: Ca, 45 g kg− 1; Na, 200 g kg− 1; Mg, 165 g kg− 1; Cu, 4250 mg kg− 1; Co, 90 mg kg− 1; I, 300 mg kg− 1; Mn, 6670 mg kg− 1; Zn, 5200 mg kg− 1; Vit. A, 600,000 iu kg− 1; Vit. D3, 100,000 iu kg− 1 and Vit. E, 5000 iu kg− 1) applied on top of the silage. The weanling progeny were accommodated in a slatted floor house and offered grass silage (first harvest for treatments HH2, HL2 and LL2 and delayed harvest for LL1) plus 1 kg (1.2 kg in Year 1) of a barley-based concentrate head− 1 daily. A low level of concentrate supplementation was used in order to maximize compensatory growth over the subsequent grazing season (McGee, 2005) as practiced in integrated calf-to-beef, grassland-based production systems.
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Table 1 Grazing and silage harvesting areas, and mean pre- and post-grazing sward heights (s.d.) for the four grassland management systems Grassland management system
Grassland use per cow unit (ha) Total grazing + silage First-harvest silage Second-harvest silage Grass sward height (cm) Year 1 total grazing season d Pre-grazing Post-grazing Year 2 total grazing season d Pre-grazing Post-grazing Year 3 total grazing season d Pre-grazing Post-grazing Year 4 total grazing season d Pre-grazing Post-grazing Mean of Years 1 to 4 Early April to August Pre-grazing Post-grazing August to late November Pre-grazing Post-grazing Total grazing season d Pre-grazing Post-grazing
HH2
HL2
LL2
LL1
0.49 0.29 a 0.21 c
0.49 0.29 a 0.21 c
0.59 0.29 a 0.21 c
0.59 0.37 b –
15.1 (5.02) 6.2 (1.43)
14.1 (5.41) 6.1 (2.06)
15.8 (5.47) 8.0 (2.75)
15.2 (3.48) 8.2 (2.13)
16.9 (5.43) 7.3 (2.28)
14.9 (5.77) 5.8 (1.51)
16.3 (6.17) 8.2 (3.68)
15.8 (5.49) 7.5 (1.91)
15.6 (3.24) 7.3 (1.73)
12.3 (3.47) 5.0 (1.32)
14.7 (3.32) 8.0 (2.22)
15.9 (3.88) 6.9 (1.48)
11.7 (3.85) 5.7 (1.92)
8.9 (4.18) 4.1 (1.64)
11.8 (3.97) 7.0 (2.11)
11.6 (3.42) 5.2 (1.44)
17.4 (3.83) 7.3 (1.54)
15.5 (4.38) 6.3 (1.49)
17.9 (4.04) 9.5 (2.46)
16.3 (4.14) 7.6 (1.63)
12.7 (3.20) 6.0 (1.79)
9.5 (2.55) 4.2 (0.83)
12.0 (2.80) 6.5 (1.71)
13.2 (3.35) 6.4 (1.61)
15.0 (3.51) 6.7 (1.66)
12.5 (3.46) 5.2 (1.16)
14.9 (3.42) 8.0 (2.08)
14.7 (3.74) 7.0 (1.62)
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. a November to late May (remainder grazed early April to late November). b November to mid-June (remainder grazed early April to late November). c Late May to mid-August (remainder grazed early April to late November). All land grazed after second-harvest silage. d Early April to late November.
2.3. Animal health Cows were vaccinated approximately 4 to 12 weeks before parturition using an E. coli and Rotavirus vaccine. Both cows and breeding heifers were vaccinated prior to commencing the breeding season against Leptospirosis. The calves were treated 2 or 3 times during the grazing season and always at housing for the control of lung and gastrointestinal worms. In spring each year, the grazing area was dusted with calcined magnesite (32 kg ha− 1) to prevent hypomagnesaemia in the cows. In autumn, hypomagnesaemia control measures involved free access to a 50:50 calcined magnesite/molasses mixture. 2.4. Measurements The pre- and post-grazing grass height was estimated using a sward stick with an average of 40 measurements per paddock as described by O'Riordan and O'Kiely (1996). Representa-
tive samples of the silage were obtained and the dry matter (DM) concentration was determined after drying at 40 °C for 48 h in an oven with forced air circulation and the in vitro dry matter digestibility (DMD) was determined as described by Tilley and Terry (1963). Silage juice extracts were used to determine pH. Cow and calf liveweight was recorded within 20 h of parturition, at turnout to pasture, intermittently during the grazing season, at weaning and at housing. The weanling progeny were again weighed approximately four weeks posthousing (to account for any potential differences in liveweight due to variation in gut fill) and at the end of indoor winter period as yearlings. Cow body condition score (BCS) was assessed at the same time as weighing as described by Lowman et al. (1976), with a scale of 0 to 5, where 0 represented emaciated and 5 represented obesity. Milk yield was determined in Years 3 and 4 using the weigh–suckle–weigh procedure (McGee et al., 2005). In Year 3, five estimates were obtained at approximately 28 day
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3. Results 3.1. Weather, grass production and silage composition
Fig. 1. Daily herbage growth rates at Grange Beef Research Centre.
intervals from June to October inclusive and in Year 4, three estimates were obtained in June, August and September. 2.5. Statistical analysis Data were subjected to an analysis of variance using PROC GLM (SAS, 2003). Data pertaining to the cows were analysed with a model that included terms for grassland management system, year, system × year and cow block within year. Calf data were analysed with additional terms for calf sex and sire. Milk yield data were subjected to analysis of variance with repeated measures using the PROC MIXED procedure of SAS (2003). Least-square means are reported with standard errors.
Annual rainfall figures for 1992, 1993, 1994 and 1995 were 789, 978, 886 and 909 mm, respectively. This compares with the 30-year (1971–2001) average of 849 mm. In 1995 there was only 3.7 mm of rainfall in August compared to the long-term average of 72.1 mm. Correspondingly, annual duration of sunshine hours were 1003, 1217, 1169 and 1399 and mean daily ground temperatures were 7.8, 10.5, 9.3 and 9.9 °C. These compare with the 30-year average of 1230 h and 9.1°C. Annual grass yields were 13.0, 11.9 and 10.2 t DM ha− 1 for 1993, 1994 and 1995, respectively (Fig. 1). Annual grass production for the period 1993 to 2001 averaged 11.9 t DM ha− 1. Mean sward heights pre- and post-grazing are presented in Table 1. Pre-grazing sward heights were numerically lowest for HL2 over the entire grazing season followed by LL1 for the first part of the season and LL2 in the second part of the season. Postgrazing sward heights were numerically lowest for HL2 followed by HH2 for all the grazing season. The mean DM, in vitro DMD and pH values for the four years for the early and late first-harvest silage were 234
Table 2 Cow liveweight and liveweight changes, body condition score and their changes, and calving interval under four grassland management systems SEM 1
Grassland management system HH2 Live weight (kg) Turnout to grass Live weight change (kg) Turnout to mid-June (55 days) Mid-June to weaning Mid-June to housing Grazing season Annual 2 Body condition score (scale 1–5) Turnout to grass Body condition score change Turnout to mid-June (55 days) Mid-June to housing Grazing season Annual 2 Calving interval (days)
HL2
LL2
LL1
512
514
509
505
7.9
54 51a 55a 110ac 39a
51 20b 35b 86b 25b
62 40c 45c 107a 45a
54 73d 67d 119c 41a
3.6 3.2 3.7 4.6 5.6
2.2
2.2
2.3
2.1
0.08
0.60a 0.26a 0.86ac 0.02ab 370
0.60a − 0.11b 0.50b − 0.16a 364
0.60a 0.14a 0.73a 0.08ab 364
0.31b 0.68c 0.98c 0.23b 367
0.065 0.065 0.069 0.103 3.8
Sig.
⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎ ⁎
⁎⁎ ⁎⁎⁎ ⁎⁎⁎ ⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. 2 From turnout to pasture to following turnout to pasture. abcd Values with different superscripts differ significantly (P b 0.05). ⁎P b 0.05, ⁎⁎P b 0.01, ⁎⁎⁎P b 0.001.
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(s.d. 33.9) g kg− 1, 725 (s.d. 28.3) g kg− 1 and 3.7 (s.d. 0.22), and 236 (s.d. 19.1) g kg− 1, 682 (s.d. 59.4) g kg− 1 and 3.7 (s.d. 0.15), respectively. The corresponding values for the second-harvest silage were 268 (s.d. 52.8) g kg− 1, 646 (s.d. 12.1) g kg− 1 and 3.8 (s.d. 0.13). 3.2. Cow liveweight and body condition score Cow liveweight gain during the first 55 days at grass did not differ (P N 0.05) between the Systems. From June to weaning and from June to housing, liveweight gain differed (P b 0.001) between all Systems being lowest for HL2 followed by, in ascending order, LL2, HH2 and LL1. The duration of the grazing season was 220, 213, 220 and 222 days for Systems HH2, HL2, LL2 and LL1, respectively. Liveweight gain for the entire grazing season was higher (P = 0.05) for LL1 than LL2 with HH2 being intermediate (P N 0.05), whereas liveweight gain of HL2 was lower (P b 0.001) than the other three Systems. Following a similar feeding regime over the indoor winter period, annual liveweight change was lower (P b 0.05) for HL2 than the other three Systems, which did not differ (P N 0.05). During the first 55 days at grass, BCS gain was lower (P b 0.01) for cows in LL1 than the other three Systems, which did not differ (P N 0.05). From June until housing, cows on System HL2 had lower (P b 0.01) BCS gains than cows in HH2 and LL2 who in turn, were lower (P b 0.001) than LL1 (Table 2). Body condition score gain over the entire grazing season was higher (P b 0.01) for LL1 than LL2 with HH2 being intermediate (P N 0.05), whereas cows on System HL2 had a lower (P b 0.05) body condition score gain than the other three Systems. Annual body condition score change was lower (P b 0.01) for HL2 than LL1 with HH2 and LL2 being intermediate (P N 0.05).
Table 3 Cow milk yield (SEM 1) in Years 3 and 4 under four grassland management systems Grassland management system HH2 Milk yield (kg/day) Year 3 9.5 (0.62) Year 4 7.8ab (0.53)
Fig. 2. Milk yield on the four grassland management systems in Year 3.
3.3. Other parameters Calving interval did not differ (P N 0.05) between the grassland management Systems (Table 2). Pregnancy rates were 0.93, 0.93, 1.00 and 0.93 for Systems HH2, HL2, LL2 and LL1, respectively. 3.4. Milk yield There was no significant difference in milk yield between the grassland management Systems in Year 3 but in Year 4 milk yield was lower (P b 0.01) for HL2 than LL2 or LL1 with HH2 being intermediate (P N 0.05) (Table 3). There was no System × time interaction in Year 3 but in Year 4 there was (P b 0.01), whereby the decline in milk yield as lactation progressed was greater for HL2 than the other three Systems (Figs. 2 and 3). 3.5. Progeny performance Calf liveweight gain from turnout to grass until housing at the end of the grazing season was lower (P b 0.05) for HL2 than HH2 who in turn were lower (P b 0.05) than LL1 whereas calves from System LL2 were intermediate (P N 0.05) to HH2 and LL1 (Table 4). Liveweight gain from turnout to grass until 28 days post-housing was lower (P b 0.01) for HL2 than LL1 with HH2 and LL2 being intermediate (P N 0.05). Calves
Sig.
HL2
LL2
LL1
8.3 (0.62) 6.8a (0.50)
8.6 (0.62) 8.7b (0.46)
9.3 (0.63) 8.7b (0.50)
NS ⁎⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. ab Values with different superscripts differ significantly (P b 0.05). ⁎⁎P b 0.01.
Fig. 3. Milk yield on the four grassland management systems in Year 4.
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Table 4 Calf live weight and live weight gain on the four grassland management systems Grassland management system HH2 Live weight (kg) At birth (16 March) At turnout to grass (20 April) At housing (22 October) 28 days post-housing 13 months (yearling) (8 April)
HL2
LL2
SEM 1
Sig.
LL1
46 77 296a 313 400
45 72 281b 304 396
45 74 299a 314 410
45 74 306a 320 388
1.3 3.5 8.1 8.3 9.5
⁎⁎
Live weight gain (kg) Turnout to grass to housing (186 days) Turnout to grass to 28 days post-housing Housing to 13 months (174 days)
220a 236ab 106a
209b 231a 116b
225ac 239ab 111ab
231c 246b 83c
5.7 5.9 4.5
⁎⁎⁎ ⁎ ⁎⁎⁎
Daily gain (g) Turnout to grass to housing (186 days)
1185a
1128b
1211ac
1256c
27.9
⁎⁎⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. abc Values with different superscripts differ significantly (P b 0.05). ⁎P b 0.05, ⁎⁎P b 0.01, ⁎⁎⁎P b 0.001.
from HL2 had a lower (P b 0.05) liveweight at housing than the other three Systems, which did not differ (P N 0.05). However, liveweight recorded four weeks after housing did not differ (P N 0.05) between the four Systems. During the subsequent winter indoor period, liveweight gain of calves from HL2 was higher (P b 0.05) than HH2 with LL2 being intermediate (P N 0.05), whereas calves from LL1 had a lower (P b 0.001) liveweight gain than the other three Systems. At the end of the indoor winter period liveweight did not differ (P = 0.08) between the four Systems. 4. Discussion There is a general need to incorporate findings from component research into beef suckler cow production systems research (Wright et al., 1996; Adams et al., 2000). It is accepted that in systems experiments it is often difficult to replicate treatment groups (Adams et al., 2000; Milne, 2006). Replication of Systems in the present study would have required substantially higher resources. Using grazing experiments in Ireland, Conniffe (1976) found that between-animal–within-herd variation accounted for most of the variation between herds within grazing treatments. Consequently, using the individual animal as the experimental unit should not affect the conclusions drawn. Furthermore, considering the randomization of the experimental area initially and of the cows to the Systems annually and, the fact that this study was carried out over four years, this increases the
likelihood that the results obtained reflect the effects of the management Systems under investigation. 4.1. Grass measurements The pasture heights both pre- and post-grazing were indicative of the stocking rate and fertiliser N levels used in the Systems and the grass growth potential due to soil and environmental conditions. Previous studies with continuous grazing or set-stocked systems have shown that maximum cow and calf performance occurred when sward surface height was maintained at 8 to 10 cm, although to prevent excessive development of reproductive tillers, sward surface heights should be below 8 cm in the first half of the grazing season (Wright et al., 1996). Swards continuously grazed to 4 to 5 cm have resulted in reductions in cow herbage intake, liveweight gain, milk yield and calf liveweight gain (e.g. Wright et al., 1994). The results of the present study indicate, that in a rotationally grazed system, good cow and calf performance were obtained from uncompressed sward post-grazing heights of approximately 7.5 to 9.0 cm (with corresponding pre-grazing heights of approximately 17.5 cm) in the first half of the grazing season (HH2 and LL2 vs. HL2) and post-grazing heights of approximately 6.0 to 6.5 cm (with corresponding pregrazing heights of approximately 12.5 cm) in the second half of the grazing season (HH2, LL2 and LL1 vs. HL2). Drennan et al. (2005b), using a rising plate meter, reported average pre- and post-grazing heights for the
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total grazing season in rotationally grazed systems ranging from 10.9 to 12.6 cm pre and 5.7 to 6.3 cm post, respectively. It is important to note that the sward heights in the present study were uncompressed and would be 1 to 2 cm higher than values obtained with a plate meter at lower sward heights (4 to 6 cm), whereas in taller swards the magnitude of the difference is greater (O'Riordan and O'Kiely, 1996). While herbage samples were not obtained for analyses in the present study, the main differences of magnitude in herbage chemical composition or nutritional value between well-managed, low and high N systems is likely to be crude protein concentrations, reflecting the difference in fertiliser N application (Keane and Allen, 1999; Audic et al., 2002; Drennan et al., 2005b). 4.2. Cow liveweight and body condition score For economic reasons beef suckler cow nutrition on farms involves mobilisation of cow body reserves in winter and subsequent recovery during the grazing season (Petit et al., 1995), the extent depending on herbage supply. The lower BCS gain over the grazing season by cows in System HL2 compared to HH2 and LL2 is consistent with previous studies that have compared the effects of high SR or low herbage allowances with low SR or high herbage allowances (Wright et al., 1994, 1996). The corresponding liveweight gain reflected the BCS gain. Similar to the present findings for Systems HH2 and LL2, Audic et al. (2002) found that decreasing SR by about 0.23 and N fertilisation rate by about 0.63 did not adversely affect the liveweight gain of beef suckler cows on rotationally grazed systems. Although not reflected in cow weight changes, the lower BCS gains on System LL1 during the first half of the grazing season compared to the other three systems may partly be attributed to the high proportion of the total area closed for first-harvest silage and thus, their provision with insufficient grass, which could have negative implications for cow reproductive performance (Drennan and Berry, 2006). Because rumen contents can account for 0.15 to 0.25 of total liveweight gain of beef cows at grass (Agabriel et al., 1993) liveweight gain may not be the best indicator of body reserve deposition at pasture particularly where herbage allowance differs. The lower liveweight and BCS gains of cows on LL2 than LL1 during the second half of the grazing season is probably a reflection of a lower grass supply and additionally, possibly lower quality herbage in the latter part of the year as a result of under-grazing early in the season (Stakelum and Dillon, 1990).
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The high replenishment of body reserves during the total grazing season for Systems HH2, LL2 and LL1 (+ 107 to 119 kg liveweight and +0.73 to 0.98 BCS units) are similar to gains in liveweight and BCS previously obtained at this centre (+ 103 kg live weight and 0.94 BCS units) for rotationally grazed spring-calving beef suckler cows (Drennan and McGee, 2004). 4.3. Milk yield and calf performance The greater decline in milk yield as lactation progressed in Year 4 than Year 3 can be associated with the poor grass growth (Fig. 1) due to a soil moisture deficit in that year and consequently, a lower pasture supply as indicated by the lower pre- and post-grazing sward heights. Similarly, the greater decline in milk yield for HL2 in Year 4 than the other systems reflects the lower grass supply. These results are in accord with Wright and Russel (1987) who found that the persistency of lactation was adversely affected when cows grazed to a lower post-grazing height. The lower milk yield in HL2 compared to HH2 (P = 0.09) and LL2 (P b 0.01) in Year 4 is consistent with previous studies, which have shown that cows on high SR or offered low herbage allowances have lower milk yields [and greater cow liveweight and (or) body condition loss (or lower weight and condition gains)] than cows on lower SR or offered higher herbage allowances and consequently, their calves generally have lower liveweight gains (Drennan, 1971a,b; Baker et al., 1981a,b, 1982; Wright et al., 1994). When feed supply is inadequate, beef suckler cows partition nutrients towards milk production rather than body reserve deposition and thus, milk lessens the adverse impact of feed restriction on the suckling calf (Petit et al., 1995). However, with prolonged undernutrition milk yield will be adversely affected. When milk supply to the calf decreases grass intake usually increases but this substitution is generally insufficient to offset a decline in calf growth resulting from decreased milk production (Wright and Russel, 1987) as was evident in the lighter liveweight at housing of calves from System HL2. This can have important implications for calf-to-beef production as data shows that in springcalving, temperate pasture based-systems, liveweight differences at weaning are largely retained until slaughter (Drennan and McGee, 2004; Drennan et al., 2005a). However, the subsequent absence of a difference between Systems in the post-housing calf weight indicates that some of the weight differences at housing were due to gut-fill differences, which would be expected to be lower for HL2 animals due to limited
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grass supplies. Consequently, the subsequent higher weight gain during the winter period of calves in HL2 than HH2 was likely to be partly attributed to a lower initial weight of gut contents. The lower liveweight gain during the winter period of calves in LL1 can be attributed to a lower nutrient supply from the grass silage as a result of the 14 day delay in harvesting date. Herbage digestibility decline of this magnitude due to delayed harvest date has been reported by Keating and O'Kiely (2000). In agreement with the results for Systems HH2 and LL2, Audic et al. (2002) found that decreasing SR by about 0.23 and nitrogen fertilisation rate by about 0.63 did not adversely affect the liveweight gain of suckling calves on rotationally grazed systems. The liveweight gains of the calves were in excess of 1.1 kg day− 1 over the grazing season. These values are similar to previous reports where grass supply was not limited on spring-calving rotationally grazed, temperate grassland systems (Drennan and McGee, 2004; Audic et al., 2002; Drennan et al., 2005b) although the magnitude can be largely influenced by the milk yield of the dam (McGee et al., 2005). 4.4. Liveweight output and nitrogen balance hectare− 1 The output of weaned calf ha− 1 was 604, 573, 507 and 518 kg for Systems HH2, HL2, LL2 and LL1, respectively. The differences in liveweight of calves weaned ha− 1 between Systems HH2 and LL2 was attributed to differences in SR because individual animal performance was similar. Wright et al. (1996) comparing set-stocking rates of 2.5 and 2.0 cows ha− 1 on perennial ryegrass swards obtained a liveweight of calves weaned ha− 1 of 550 and 456 kg, respectively whereas Wright et al. (1994) comparing contrasting sward heights reported equivalent weights ranging from 348 to 413 kg ha− 1. The output of yearling calf liveweight ha− 1 was 816, 808, 695 658 kg and including annual cow weight gain increased total output to 896, 859, 771 and 727 kg ha− 1, for Systems HH2, HL2, LL2 and LL1, respectively. Surplus N within grassland-based production systems is susceptible to loss to the wider environment. In accord with previous studies (Lawes et al., 2000), only small proportions of the N inputs were converted to animal product i.e. liveweight gain. The purchased N inputs to these Systems were limited to chemical fertiliser and concentrate supplement. Assuming a crude protein content of 140 g kg− 1 in the purchased concentrate, equivalent to 22.4 g N kg− 1, this equated to an intake of 4.1 kg of N per weanling animal.
Combining the chemical fertiliser N applied, the total purchased N input was 227, 154, 138 and 121 kg ha− 1 for Systems HH2, HL2, LL2 and LL1, respectively. Ignoring N sequestered in the soil and assuming a N content of liveweight gain of 28 g kg− 1 (Lawes et al., 2000) the corresponding N removal by the cow and calf was 25, 24, 22 and 20 kg ha− 1 equating to a N surplus of 202, 130, 116 and 101 kg ha− 1 for Systems HH2, HL2, LL2 and LL1, respectively. (This calculation assumes that all the slurry produced from the cows and progeny was returned to the respective systems, and disregards the surplus herbage grazed by non-experimental animals in Years 1 and 2). In accord with previous findings, reducing fertiliser N use can reduce the N surplus in beef systems (Lawes et al., 2000) and consequently, the pollution risk. Richards et al. (2007) found that when compared to high SR–high fertiliser N beef systems, nitrate leaching was significantly lower in low SR–low fertiliser N beef systems. The N-use efficiency (N output input− 1 ha− 1) for Systems HH2, HL2, LL2 and LL1 were 0.11, 0.16, 0.16 and 0.17, respectively. Dieguez Cameroni et al. (2006) reported an apparent N efficiency of 0.13, 0.15 and 0.26 during the grazing period for growing fattening bulls on high N–high SR, moderate N–high SR and zero N–low SR systems, respectively. From a review of the literature Peyraud and Astigarraga (1998) concluded that lowering levels of N fertilisation (with an appropriate reduction in SR) appeared to be an effective means of reducing N losses of ruminants in grazing systems with little or no change in the animals nutrition or in their individual output. Consequently, the main effect was a decrease in animal output per unit land area. 4.5. Additional considerations According to Gibon (2005) there is a greater need to move from the idea of grassland as a resource for animal production to grassland as a complex agro-ecosystem to be managed at a variety of scales of multifunctionality. Reducing fertiliser inputs and SR has the potential to facilitate the restoration of diverse swards (Isselstein, 2005; Isselstein et al., 2005) and it is believed that agrienvironmental schemes will play an increasing role in achieving biodiversity in the future (Isselstein, 2005). Furthermore, participation by beef farmers in environmental schemes such as REPS can be financially attractive (Crosson et al., 2006). In terms of organic N input, assuming that all the slurry produced from the cows and progeny was returned to the respective systems, the low N, low SR Systems were compatible with the Nitrates Directive of the EU (Directive 91/676/
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EEC), which was subsequently introduced and which limits organic N to 170 kg ha− 1. Additionally, System LL1 verges on compatibility with the REPS operated in Ireland to date, where the maximum permissible level of organic (including grazing deposition) N is 170 kg ha− 1 annum− 1 and total (organic plus chemical) N is 260 kg ha− 1 annum− 1. At the stipulated annual organic N loads of 65, 24 and 57 kg for a beef suckler cow, animals 0–1 and 1–2 years old, respectively, the total organic N on the high and low SR systems was 191 and 159 kg ha− 1, in that order. Addition of the chemical fertiliser N applied gave a total N input of 410, 337, 289 and 273 kg ha − 1 for Systems HH2, HL2, LL2 and LL1, respectively. As the vast proportion of liveweight gain on the current systems was obtained from grazed and conserved grass, bringing animals to slaughter on similar grass-based systems may enhance the content of beneficial fatty acids and improve the stability of meat in comparison to alternative systems, such as highconcentrate diets (McGee, 2005; Scollan et al., 2005). 5. Conclusions Increasing the level of fertiliser N application at the high SR or reducing the SR at the low level of N, increased cow liveweight and BCS gain at pasture and prolonged the grazing season. Good cow and calf performance at pasture was obtained in both the high SR and high N, and low SR and low N Systems, indicating a successful substitution of fertiliser N by additional land area. While at low SR, the winter grass silage requirements could be provided in one delayed harvest as opposed to two harvests thereby reducing the conservation area (and associated costs kg− 1 DM), but delayed harvesting of silage resulted in lower digestibility and reduced calf performance in winter. An alternative option for a low SR, low N System may be midway between Systems LL2 and LL1 by having a planned, staggered, one-harvest silage system where the early-harvest provides high digestibility grass silage for the progeny and the later delayed harvest adequate nutritive value silage for the cow, but this needs to be quantified. Such an adjustment would be necessary for the one-harvest System in order to provide an adequate herbage supply early in the grazing season to offset the possible adverse effect on cow reproductive performance. This study indicated the specifications for a lower fertiliser N grassland system, particularly where qualification for EU environmental schemes is dependent on moderate stocking densities.
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Acknowledgements The authors wish to acknowledge the farm staff at Grange Research Centre for care and management of the animals and M. Greally for skilled technical assistance. Also thanks to the staff of Grange Laboratories for grass silage analyses. References Adams, D.C., Nielsen, M.K., Schacht, W.H., Clarke, R.T., 2000. Designing and conducting experiments for range beef cows. Proc. Am. Soc. Anim. Sci. 1999. Agabriel, J., Petit, M., Giraud, J.M., 1993. Rumen contents of Charolais cows during the grazing period. Ann. Zootech. 42, 162. Audic, C., Hardy, A., Pelletier, P., 2002. Extensification of grazed pastures in French suckling cow systems. Grassl. Sci. Europe 7, 1008–1009. Baker, R.D., Alvarez, F., Le Du, Y.L.P., 1981a. The effect of herbage allowance upon the herbage intake and performance of suckler cows and calves. Grass Forage Sci. 36, 189–199. Baker, R.D., Le Du, Y.L.P., Alvarez, F., 1981b. The herbage intake and performance of set-stocked suckler cows and calves. Grass Forage Sci. 36, 201–210. Baker, R.D., Barker, J.M., Le Du, Y.L.P., 1982. The influence of winter nutrition, grazing system and stocking rate on the performance on spring-calving Hereford × Friesian cows and their calves 2. Grazing system and stocking rate. Anim. Prod. 34, 225–237. Conniffe, D., 1976. A comparison of between and within herd variance in grazing experiments. Ir. J. Agric. Res. 15, 39–46. Crosson, P., O'Kiely, P., O'Mara, F.P., Wallace, M., 2006. The development of a mathematical model to investigate Irish beef production systems. Agric. Syst. 89, 349–370. Dieguez Cameroni, F., Hornick, J., Cabaraux, J., Istasse, L., Dufrasne, I., 2006. Less intensified grazing management with growing fattening bulls. Anim. Res. 55, 105–120. Dillon, P., Berry, D.P., Evans, R.D., Buckley, F., Horan, B., 2006. Consequences of genetic selection for increased milk production in European seasonal pasture based systems of milk production. Livest. Sci. 99, 141–158. Drennan, M., 1993. Planned Suckler Beef Production. Teagasc, p. 72. Beef Series No. 4. Drennan, M.J., 1971a. Single-suckled beef production 1. Influence of stocking rate during the grazing season, creep grazing of the calf and double-suckling on live weight changes and milk production of the cows. Ir. J. Agric. Res. 10, 287–295. Drennan, M.J., 1971b. Single-suckled beef production 2. Influence of stocking rate during the grazing season, creep grazing of the calf and double-suckling on calf performance. Ir. J. Agric. Res. 10, 297–305. Drennan, M.J., McGee, M., 2004. Effect of suckler cow genotype and nutrition level during the winter on voluntary intake and performance and on the growth and slaughter characteristics of their progeny. Ir. J. Agric. Food Res. 43, 185–199. Drennan, M.J., Berry, D.P., 2006. Factors affecting body condition score, liveweight and reproductive performance in spring-calving suckler cows. Ir. J. Agric. Food Res. 45, 25–38. Drennan, M.J., McGee, M., Keane, M.G., 2005a. Post-weaning performance and carcass characteristics of steer progeny from different suckler cow breed types. Ir. J. Agric. Food Res. 44, 195–204.
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Drennan, M.J., McGee, M., Kyne, S., O'Neill, B., 2005b. Spring calving suckler beef systems: influence of grazing system on herbage availability, utilisation, quality and cow and calf performance to weaning. In: O'Mara, F.P., Wilkins, R.J., Mannetje, L.'t, Lovett, D.K., Rogers, P.A.M., Boland, T.M. (Eds.), XX International Grassland Congress: Offered Papers. Wageningen Academic Publishers, The Netherlands, p. 167. Fitzgerald, D.A., Fitzgerald, D.L., 2004. Meteorological measurements. In: Keane, T., Collins, J.F. (Eds.), Climate, Weather and Irish Agriculture. Met Eireann, Dublin, Ireland, pp. 9–26. Gardiner, M.J., 1962. Animal Production Research Centre, Grange, Co. Meath (Soil Map), Soil Survey Bulletin No. 2. An Foras Taluntais, Dublin, Ireland. Gately, T.F., 1994. Soil Analysis and Fertiliser, Lime, Animal Manure and Trace Element Recommendations. Teagasc, Johnstown Castle, Wexford, Ireland, p. 36. Gibon, A., 2005. Managing grassland for production, the environment and the landscape. Challenges at the farm and the landscape level. Livest. Prod. Sci. 96, 11–31. Isselstein, J., 2005. Enhancing the biodiversity and its consequences for grassland management and utilisation. In: McGilloway, D.A. (Ed.), Grassland: a Global Resource. Wageningen Academic Publishers, The Netherlands, pp. 305–320. Isselstein, J., Jeangros, B., Pavlu, V., 2005. Agronomic aspects of biodiversity targeted management of temperate grasslands in Europe — a review. Agron. Res. 3, 139–151. Keane, M.G., Allen, P., 1999. Effects of pasture fertiliser N level on herbage composition, animal performance and on carcass and meat quality traits. Livest. Prod. Sci. 61, 233–244. Keating, T., O'Kiely, P., 2000. Comparison of old permanent grassland, Lolium perenne and Lolium multiflorum swards grown for silage 4. Effects of varying harvesting date. Ir. J. Agric. Food Res. 39, 55–71. Lawes, J.A., Pain, B.F., Jarvis, S.C., Scholefield, D., 2000. Comparison of grassland management systems for beef cattle using self-contained farmlets: effects of contrasting nitrogen inputs and management strategies on nitrogen budgets, and herbage and animal production. Agric. Ecosyst. Environ. 80, 243–254. Lowman, B.G., Scott, N.A., Somerville, S.H., 1976. Condition scoring of cattle. Bulletin, no. 6, (Revised edition). East of Scotland College of Agriculture, p. 31. McGee, M., 2005. Recent developments in feeding beef cattle on grass silage-based diets. In: Park, R.S., Stronge, M.D. (Eds.), Silage Production and Utilisation, Proceedings of the XIVth International Silage Conference (a Satellite Workshop of the XXth International Grassland Congress), July 2005, Belfast, Northern Ireland. Wageningen Academic Publishers, The Netherlands, pp. 51–64. McGee, M., Drennan, M.J., Caffrey, P.J., 2005. Effect of suckler cow genotype on milk yield and pre-weaning calf performance. Irish J. Agric. Food Res. 44, 185–194.
Milne, J.A., 2006. Editorial. Grass Forage Sci. 61, 1. O'Kiely, P., Moloney, A.P., Killen, L., Shannon, A., 1997. A computer program to calculate the cost of providing ruminants with homeproduced feedstuffs. Comput. Electron. Agric. 19, 23–36. O'Riordan, E.G., 1997. Effect of annual application rate and grass growth interval on annual herbage production. Proc. Agric. Res. Forum, Belfield, Dublin, 3rd and 4th April, pp. 133–134. O'Riordan, E.G., O'Kiely, P., 1996. Potential of beef production systems based on grass. Ir. Grassl. Anim. Prod. Assoc. J. 30, 185–217. Petit, M., Garel, J.P., D'Hour, P., Agabriel, J., 1995. The use of forages by the beef cow herd. In: Journet, M., Grenet, E., Farce, M.-H., Theriez, M., Demarquilly, C. (Eds.), Recent Developments in the Nutrition of Herbivores. Proceedings of the IVth International Symposium on the Nutrition of Herbivores. INRA, Editions, Paris, pp. 473–496. Peyraud, J.L., Astigarraga, L., 1998. Review of the effect of nitrogen fertilization on the chemical composition, intake, digestion and nutritive value of fresh herbage: consequences on animal nutrition and N balance. Anim. Feed Sci. Technol. 72, 235–259. Richards, K., Drennan, M., Lenehan, J.J., Connolly, J., Brophy, C., Carton, O.T., 2007. Nitrate leaching from Irish beef farming, a look at the impact of REPS. Proc. Agric. Res. Forum. Teagasc, Tullamore, Ireland, p. 3. Scollan, N.D., Dewhurst, R.J., Moloney, A.P., Murphy, J.J., 2005. Improving the quality of products from grassland. In: McGilloway, D.A. (Ed.), Grassland: a Global Resource. Wageningen Academic Publishers, The Netherlands, pp. 41–56. Stakelum, G., Dillon, P., 1990. Influence of sward structure and digestibility on intake and performance of lactating and growing cattle. In: Mayne, C.S. (Ed.), Management Issues for the Grassland Farmer in the 1990s, Br. Grassl. Soc., Occasional. Pub. No. 25, pp. 30–42. Statistical Analysis Systems Institute, 2003. SAS/STAT. The SAS System for Windows, Release 9.3.1. SAS Institute Inc., Cary, NC, USA. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104–111. Wright, I.A., Russel, A.J.F., 1987. The effect of sward height on beef cow performance and on the relationship between calf milk and herbage intakes. Anim. Prod. 44, 363–370. Wright, I.A., Jones, J.R., Maxwell, T.J., Russel, A.J.F., Hunter, E.A., 1994. The effect of genotype × environment interactions on biological efficiency in beef cows. Anim. Prod. 58, 197–207. Wright, I.A., Maxwell, T.J., Russel, A.J.F., Hunter, E.A., Hetherington, R.A., Whyte, T.K., 1996. The effect of grazed sward height and stocking rate on animal performance and output from beef cow systems. Grass Forage Sci. 51, 199–208.
Livestock Science 117 (2008) 238 – 248 www.elsevier.com/locate/livsci
Performance of spring-calving beef suckler cows and their progeny on four contrasting grassland management systems M.J. Drennan ⁎, M. McGee Teagasc, Grange Beef Research Centre, Dunsany, Co. Meath, Ireland Received 16 April 2007; received in revised form 6 December 2007; accepted 11 December 2007
Abstract Data were collected over four consecutive years from four, rotationally grazed, grassland management systems each with 15 spring-calving beef suckler cows and their progeny to 13 months of age. The Systems were high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests — HH2; high SR, low N, 2 silage harvests — HL2; low SR, low N, 2 silage harvests — LL2, and low SR, low N, 1 silage harvest — LL1. High and low SR were 0.49 and 0.59 ha cow− 1 unit, respectively, and high and low N amounted to an annual input of 239 and 57 kg ha− 1 on the grazing areas, respectively. Where applicable, the four Systems received 114 and 80 kg of N ha− 1 for the first and second silage harvests, respectively. Equal areas of Systems HH2, HL2 and LL2 were conserved as silage (0.29 and 0.21 ha for first (24 May) and second (4 August) harvests, respectively cow− 1 unit) each year. Silage from System LL1 (0.37 ha cow− 1 unit) was conserved 14 days after the other first harvests. Following the final harvesting for silage within any System these areas of grassland were then grazed. During the winter all animals were housed and cows were offered grass silage and calves were offered silage plus 1 kg of concentrate per head daily. Good cow and calf performance at pasture were obtained at both high SR and high N or low SR and low N. At the high SR, increasing the level of fertiliser N application increased cow liveweight gain at pasture by 24 kg, improved body condition score (BCS) gain at pasture by 0.36 units and prolonged the grazing season by 7 days. Similarly, at the low level of fertiliser N, reducing the SR, increased cow liveweight gain at pasture by 21 kg, improved BCS gain at pasture by 0.23 units and prolonged the grazing season by 7 days. At the low SR all the winter silage requirements could be provided in one as opposed to two harvests thereby reducing the conservation area. However, delayed harvesting of silage resulted in lower silage digestibility and reduced calf performance in winter. The results indicate the specifications for a planned lower N grassland system, particularly where qualification for EU environmental schemes is dependent on moderate stocking densities. © 2007 Elsevier B.V. All rights reserved. Keywords: Beef suckler cow; Cattle; Grassland systems
1. Introduction
⁎ Corresponding author. Tel.: +353 46 9061100; fax: +353 46 9026154. E-mail address: [email protected] (M.J. Drennan). 1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2007.12.018
In many parts of Northern and Western Europe, current climatic conditions dictate that grass, either grazed or conserved, is the principal forage for beef cow and calf (suckler beef) production. Beef suckler cows are kept in a
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wide range of lowland nutritional environments, varying from high stocking rates (SR) and high inputs of nitrogenous (N) fertiliser to lower variable input systems with low SR, low inputs of N and potentially only one silage harvest. Many farmers will now need to operate to lower input criteria than heretofore, as determined by environmental legislation and (or) stipulated in environmental schemes such as the European Union (EU) Rural Environmental Protection Scheme (REPS). Due to an increasing environmental focus, the emphasis will be to restrict the application of N fertilisers and consequently, grassland management systems will reduce in intensity. Within the context of a grassland-based springcalving suckler beef production system, matching grass supply to animal requirements during the grazing season, while ensuring sufficient silage is produced for the indoor winter period, is largely achieved by balancing the use of fertiliser N and SR by altering the emphasis on harvesting grass by grazing or as silage. Thus, whereas harvesting grass for silage facilitates the concurrent and subsequent utilisation of grass by grazing (McGee, 2005), and the use of two silage harvests have traditionally been advocated for springcalving suckler beef production systems (Drennan, 1993), the considerable cost often associated with a second-harvest silage (O'Kiely et al., 1997) makes it necessary to consider replacing the two-harvest system with a simpler one-harvest system. There is very little information available on beef suckler cow grassland management systems, especially springcalving systems on rotationally grazed, temperate lowland pasture. This contrasts markedly with the number of studies published on spring-calving dairy cow grassland-based systems (e.g. Dillon et al., 2006). However, the nutritional requirements of the spring-calving dairy cow are much higher than the beef suckler cow and consequently, energy balance and performance of the dairy cow would be markedly different and more sensitive to changes in nutrient supply. Furthermore, the SR and fertiliser N inputs of dairy systems to date are generally much higher than beef systems. This makes it difficult to import results from grassland dairy systems to beef systems. The objectives of this study were to determine the effects of (1) reducing the application of fertiliser N to the grazing area, (2) allocating more land cow− 1 unit, and (3) reducing the number of silage harvests, on cow and calf performance on rotationally grazed, cow and calf-toyearling systems. The underlying hypothesis was that, compared to a high SR and high fertiliser N input (intensive system), reducing the input of fertiliser N would result in a reduction in individual animal performance, whereas using a low fertiliser N input combined with a
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low SR would result in similar individual animal performance during the grazing season to the intensive system. Additionally, lower SR would permit adequate grass silage to be produced from one as opposed to two harvests thereby reducing costs. 2. Materials and methods The study was carried out at Teagasc, Grange Beef Research Centre (Longitude 6° 40' W; Latitude 53° 30' N; Elevation 92 m asl) over a period of 4 consecutive years (1992–1995), each year comprising a summer grazing period (April to October/November) and the subsequent indoor winter feeding period. The soil type was a moderately well drained Brown Earth of medium to high base content and of clay loam texture (Gardiner, 1962). Meteorological data were recorded at the recording station at Grange Research Centre. The instruments and standards used by Irish weather stations were described by Fitzgerald and Fitzgerald (2004). Grass production was measured in 1993, 1994 and 1995 in a separate plot experiment as described by O'Riordan (1997) involving a cutting regime to a 4 cm stubble height on a 4-week cycle using an annual fertiliser N input of 300 kg ha− 1. 2.1. Animals The animals used were spring-calving (commencing midFebruary) ≥ 7/8 Charolais cows, first-cross Hereford × Holstein–Friesian and Limousin × Holstein–Friesian cows, and their progeny. Each year the cows were bred using two Charolais sires, one by artificial insemination (A.I.) and the second by natural mating. Replacement heifers were bred to a Limousin bull (A.I.) to calve at 2 years of age and were introduced into the herd in Spring when animals were being turned out from the winter accommodation to commence grazing the grassland (i.e. turnout to grass). Average parity was 3.8 (s.d. 2.31) and calving date was 16 March (s.d. 21.4 days). The date on which grazing commenced in spring was dictated by a combination of grass supply, ground conditions and calving date, as all cows had calved prior to turnout. The average turnout date to grass for the cows and calves was 20 April (s.d. 7.5 days). 2.2. Grassland management systems The experimental area was a permanent grassland site comprising 32.5 ha. A total of 32 paddocks were grouped into 8 sets of four (balanced for location and soil type) and randomly assigned to four grazing management systems. The area assigned to the high and low SR systems was 7.36 and 8.88 ha, respectively. Average paddock size was 1.02 ha (ranged from 0.56 to 1.42 ha) and each paddock had its own water supply. For the two high SR systems, paddocks were of equal size within each set of four, whereas for the two low SR systems the area of four of the paddocks (the main grazing paddocks) was 1.5 that of the corresponding paddocks in the
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high SR systems. The paddocks assigned to grazing and silage harvesting were the same over the duration of the study. Each year at turnout to pasture, 60 cows and their progeny were blocked according to genotype, parity and calving date across four grazing management systems each with 15 cows and calves grazing together. The allocation of cows to the Systems did not take account of the treatments imposed in previous years (Wright et al., 1994; Drennan and McGee, 2004). The four Systems were: high SR, high N, 2 silage harvests — (HH2): high SR, low N, 2 silage harvests — (HL2); low SR, low N, 2 silage harvests — (LL2); and low SR, low N, 1 silage harvest — (LL1). High and low SR were 0.49 and 0.59 ha cow− 1 unit, respectively. A cow unit was defined as a cow plus progeny to 13 months of age. High and low chemical fertiliser N amounted to 239 and 57 kg ha− 1 annum− 1 on the grazing areas, respectively. In the spring, fertiliser N was applied to the grazing areas of all Systems at a rate of 57 kg ha− 1 in early March. No further fertiliser N was applied to the grazing area of Systems HL1, LL2 and LL1. System HH2 received additional applications after the first and second grazing at the rate of 57 kg N ha− 1 and two further applications of 34 kg N ha− 1 between then and 20 August. On the silage harvesting area, fertiliser N was applied at the rate of 114 and 80 kg N ha− 1 for first and second harvests, respectively. Following the final harvest of herbage for silage, 34 kg N ha− 1 was applied. For Systems HH2, HL2, LL2, and LL1 the total annual chemical fertiliser N application rate was 219, 146, 131 and 114 kg ha− 1, respectively. Urea (46% N) was generally used as the nitrogen source except in dry weather conditions when calcium ammonium nitrate (CAN; 27.5% N) was applied. Phosphorus (P) and potash (K) fertiliser application rates were based on soil test analyses (Gately, 1994). On the grazing area, a single annual application of 19 and 38 kg ha− 1 of P and K, respectively was applied in early Spring. On the silage harvesting area, the application rates of P and K were 21.5 and 92.5 kg ha− 1, respectively for both first and second silage harvests. After the single silage harvest in System LL1 an additional 18.5 and 37.5 kg ha− 1 was applied. Additional to the chemical fertiliser application, occasionally, slurry produced during the winter indoor feeding period was returned to the area harvested for silage in early Spring and again after silage harvesting at a rate proportional to the SR for the grassland management systems. The fertiliser nutrient value of the slurry was not determined. The swards consisted predominantly of perennial ryegrass (Lolium perenne) and were rotationally grazed. Botanical composition was not measured but visually there was very little white clover (Trifolium repens) present. Residency time in each paddock was the same for Systems HH2, HL2 and LL2, and was determined by visual assessment of the post-grazing grass height of System HL2, whereas animals in System LL1 were moved independently. The grazing management plan was such that all Systems completed each grazing cycle at the same time. Residency time per paddock (days) in Year 3 averaged 4.6 (s.d. 1.79) for Systems HH2, HL2 and LL2, and 6.7 (s.d. 2.13) for System LL1. Corresponding values in Year 4 were 4.3 (s.d. 2.32)
and 6.6 (s.d. 2.79) days. Equal areas of Systems HH2, HL2 and LL2 were conserved as silage (0.29 and 0.21 ha for first (24 May (s.d. 2.2 days)) and second (4 August (s.d. 5.8 days)) harvests, respectively cow− 1 unit) each year (Table 1). Silage from System LL1 (0.37 ha cow− 1 unit) was conserved 14 days after (7 June) the other first harvests. Grass was precision-chop harvested, usually with minimal wilting and with the addition of an acidbased additive when required and, ensiled in unroofed, horizontal clamps which were rolled thoroughly, before sheeting with 2 layers of polythene and covering with tyres. In the two-harvest systems the objective was to produce high nutritive value firstharvest grass silage for the weanling progeny and moderate nutritive value second-harvest silage for the cows. The cutting date of the second harvest was delayed to produce a higher yield, of lower digestibility silage (at a lower cost unit− 1 DM) as this is adequate for spring-calving beef suckler cows with relatively modest energy requirements for production (i.e. not lactating for most of the indoor winter period) (Drennan and McGee, 2004). Following the final harvest of herbage for silage, the subsequent regrowth was grazed in their respective systems. All calves were abruptly weaned in autumn at approximately 7 to 8 months of age. Weaning date for all Systems was determined by the grass supply in System HL2. Calves were removed from the pasture and housed indoors for the winter feeding period on 29, 7, 26 and 27 October in Years 1, 2, 3 and 4, respectively. Weaning coincided with housing indoors except for Year 4 when, due to poor grass growth relating to a soil moisture deficit, calves were weaned earlier than planned on 27 September and offered 1 kg day− 1 (following gradual introduction) of a barley-based concentrate supplement at pasture until housing time. After weaning, cows remained grazing at pasture until housing indoors, which was determined by grass supply and ground conditions. The average date of housing over the four years was 25, 18, 25 and 27 November for Systems HH2, HL2, LL2 and LL1, respectively. Herbage surplus to requirements on the grazing areas in Year 1 (late May/early June) and Year 2 (early May) was removed using equal numbers of yearling heifers grazing on each System equivalent to 25 and 204 yearling grazing days per System for Years 1 and 2, respectively. During the winter indoor feeding period the cows were offered grass silage (generally restricted pre-calving and ad libitum post-calving) and a mineral vitamin supplement (60 g cow− 1 day− 1: Ca, 45 g kg− 1; Na, 200 g kg− 1; Mg, 165 g kg− 1; Cu, 4250 mg kg− 1; Co, 90 mg kg− 1; I, 300 mg kg− 1; Mn, 6670 mg kg− 1; Zn, 5200 mg kg− 1; Vit. A, 600,000 iu kg− 1; Vit. D3, 100,000 iu kg− 1 and Vit. E, 5000 iu kg− 1) applied on top of the silage. The weanling progeny were accommodated in a slatted floor house and offered grass silage (first harvest for treatments HH2, HL2 and LL2 and delayed harvest for LL1) plus 1 kg (1.2 kg in Year 1) of a barley-based concentrate head− 1 daily. A low level of concentrate supplementation was used in order to maximize compensatory growth over the subsequent grazing season (McGee, 2005) as practiced in integrated calf-to-beef, grassland-based production systems.
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Table 1 Grazing and silage harvesting areas, and mean pre- and post-grazing sward heights (s.d.) for the four grassland management systems Grassland management system
Grassland use per cow unit (ha) Total grazing + silage First-harvest silage Second-harvest silage Grass sward height (cm) Year 1 total grazing season d Pre-grazing Post-grazing Year 2 total grazing season d Pre-grazing Post-grazing Year 3 total grazing season d Pre-grazing Post-grazing Year 4 total grazing season d Pre-grazing Post-grazing Mean of Years 1 to 4 Early April to August Pre-grazing Post-grazing August to late November Pre-grazing Post-grazing Total grazing season d Pre-grazing Post-grazing
HH2
HL2
LL2
LL1
0.49 0.29 a 0.21 c
0.49 0.29 a 0.21 c
0.59 0.29 a 0.21 c
0.59 0.37 b –
15.1 (5.02) 6.2 (1.43)
14.1 (5.41) 6.1 (2.06)
15.8 (5.47) 8.0 (2.75)
15.2 (3.48) 8.2 (2.13)
16.9 (5.43) 7.3 (2.28)
14.9 (5.77) 5.8 (1.51)
16.3 (6.17) 8.2 (3.68)
15.8 (5.49) 7.5 (1.91)
15.6 (3.24) 7.3 (1.73)
12.3 (3.47) 5.0 (1.32)
14.7 (3.32) 8.0 (2.22)
15.9 (3.88) 6.9 (1.48)
11.7 (3.85) 5.7 (1.92)
8.9 (4.18) 4.1 (1.64)
11.8 (3.97) 7.0 (2.11)
11.6 (3.42) 5.2 (1.44)
17.4 (3.83) 7.3 (1.54)
15.5 (4.38) 6.3 (1.49)
17.9 (4.04) 9.5 (2.46)
16.3 (4.14) 7.6 (1.63)
12.7 (3.20) 6.0 (1.79)
9.5 (2.55) 4.2 (0.83)
12.0 (2.80) 6.5 (1.71)
13.2 (3.35) 6.4 (1.61)
15.0 (3.51) 6.7 (1.66)
12.5 (3.46) 5.2 (1.16)
14.9 (3.42) 8.0 (2.08)
14.7 (3.74) 7.0 (1.62)
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. a November to late May (remainder grazed early April to late November). b November to mid-June (remainder grazed early April to late November). c Late May to mid-August (remainder grazed early April to late November). All land grazed after second-harvest silage. d Early April to late November.
2.3. Animal health Cows were vaccinated approximately 4 to 12 weeks before parturition using an E. coli and Rotavirus vaccine. Both cows and breeding heifers were vaccinated prior to commencing the breeding season against Leptospirosis. The calves were treated 2 or 3 times during the grazing season and always at housing for the control of lung and gastrointestinal worms. In spring each year, the grazing area was dusted with calcined magnesite (32 kg ha− 1) to prevent hypomagnesaemia in the cows. In autumn, hypomagnesaemia control measures involved free access to a 50:50 calcined magnesite/molasses mixture. 2.4. Measurements The pre- and post-grazing grass height was estimated using a sward stick with an average of 40 measurements per paddock as described by O'Riordan and O'Kiely (1996). Representa-
tive samples of the silage were obtained and the dry matter (DM) concentration was determined after drying at 40 °C for 48 h in an oven with forced air circulation and the in vitro dry matter digestibility (DMD) was determined as described by Tilley and Terry (1963). Silage juice extracts were used to determine pH. Cow and calf liveweight was recorded within 20 h of parturition, at turnout to pasture, intermittently during the grazing season, at weaning and at housing. The weanling progeny were again weighed approximately four weeks posthousing (to account for any potential differences in liveweight due to variation in gut fill) and at the end of indoor winter period as yearlings. Cow body condition score (BCS) was assessed at the same time as weighing as described by Lowman et al. (1976), with a scale of 0 to 5, where 0 represented emaciated and 5 represented obesity. Milk yield was determined in Years 3 and 4 using the weigh–suckle–weigh procedure (McGee et al., 2005). In Year 3, five estimates were obtained at approximately 28 day
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3. Results 3.1. Weather, grass production and silage composition
Fig. 1. Daily herbage growth rates at Grange Beef Research Centre.
intervals from June to October inclusive and in Year 4, three estimates were obtained in June, August and September. 2.5. Statistical analysis Data were subjected to an analysis of variance using PROC GLM (SAS, 2003). Data pertaining to the cows were analysed with a model that included terms for grassland management system, year, system × year and cow block within year. Calf data were analysed with additional terms for calf sex and sire. Milk yield data were subjected to analysis of variance with repeated measures using the PROC MIXED procedure of SAS (2003). Least-square means are reported with standard errors.
Annual rainfall figures for 1992, 1993, 1994 and 1995 were 789, 978, 886 and 909 mm, respectively. This compares with the 30-year (1971–2001) average of 849 mm. In 1995 there was only 3.7 mm of rainfall in August compared to the long-term average of 72.1 mm. Correspondingly, annual duration of sunshine hours were 1003, 1217, 1169 and 1399 and mean daily ground temperatures were 7.8, 10.5, 9.3 and 9.9 °C. These compare with the 30-year average of 1230 h and 9.1°C. Annual grass yields were 13.0, 11.9 and 10.2 t DM ha− 1 for 1993, 1994 and 1995, respectively (Fig. 1). Annual grass production for the period 1993 to 2001 averaged 11.9 t DM ha− 1. Mean sward heights pre- and post-grazing are presented in Table 1. Pre-grazing sward heights were numerically lowest for HL2 over the entire grazing season followed by LL1 for the first part of the season and LL2 in the second part of the season. Postgrazing sward heights were numerically lowest for HL2 followed by HH2 for all the grazing season. The mean DM, in vitro DMD and pH values for the four years for the early and late first-harvest silage were 234
Table 2 Cow liveweight and liveweight changes, body condition score and their changes, and calving interval under four grassland management systems SEM 1
Grassland management system HH2 Live weight (kg) Turnout to grass Live weight change (kg) Turnout to mid-June (55 days) Mid-June to weaning Mid-June to housing Grazing season Annual 2 Body condition score (scale 1–5) Turnout to grass Body condition score change Turnout to mid-June (55 days) Mid-June to housing Grazing season Annual 2 Calving interval (days)
HL2
LL2
LL1
512
514
509
505
7.9
54 51a 55a 110ac 39a
51 20b 35b 86b 25b
62 40c 45c 107a 45a
54 73d 67d 119c 41a
3.6 3.2 3.7 4.6 5.6
2.2
2.2
2.3
2.1
0.08
0.60a 0.26a 0.86ac 0.02ab 370
0.60a − 0.11b 0.50b − 0.16a 364
0.60a 0.14a 0.73a 0.08ab 364
0.31b 0.68c 0.98c 0.23b 367
0.065 0.065 0.069 0.103 3.8
Sig.
⁎⁎⁎ ⁎⁎⁎ ⁎⁎⁎ ⁎
⁎⁎ ⁎⁎⁎ ⁎⁎⁎ ⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. 2 From turnout to pasture to following turnout to pasture. abcd Values with different superscripts differ significantly (P b 0.05). ⁎P b 0.05, ⁎⁎P b 0.01, ⁎⁎⁎P b 0.001.
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(s.d. 33.9) g kg− 1, 725 (s.d. 28.3) g kg− 1 and 3.7 (s.d. 0.22), and 236 (s.d. 19.1) g kg− 1, 682 (s.d. 59.4) g kg− 1 and 3.7 (s.d. 0.15), respectively. The corresponding values for the second-harvest silage were 268 (s.d. 52.8) g kg− 1, 646 (s.d. 12.1) g kg− 1 and 3.8 (s.d. 0.13). 3.2. Cow liveweight and body condition score Cow liveweight gain during the first 55 days at grass did not differ (P N 0.05) between the Systems. From June to weaning and from June to housing, liveweight gain differed (P b 0.001) between all Systems being lowest for HL2 followed by, in ascending order, LL2, HH2 and LL1. The duration of the grazing season was 220, 213, 220 and 222 days for Systems HH2, HL2, LL2 and LL1, respectively. Liveweight gain for the entire grazing season was higher (P = 0.05) for LL1 than LL2 with HH2 being intermediate (P N 0.05), whereas liveweight gain of HL2 was lower (P b 0.001) than the other three Systems. Following a similar feeding regime over the indoor winter period, annual liveweight change was lower (P b 0.05) for HL2 than the other three Systems, which did not differ (P N 0.05). During the first 55 days at grass, BCS gain was lower (P b 0.01) for cows in LL1 than the other three Systems, which did not differ (P N 0.05). From June until housing, cows on System HL2 had lower (P b 0.01) BCS gains than cows in HH2 and LL2 who in turn, were lower (P b 0.001) than LL1 (Table 2). Body condition score gain over the entire grazing season was higher (P b 0.01) for LL1 than LL2 with HH2 being intermediate (P N 0.05), whereas cows on System HL2 had a lower (P b 0.05) body condition score gain than the other three Systems. Annual body condition score change was lower (P b 0.01) for HL2 than LL1 with HH2 and LL2 being intermediate (P N 0.05).
Table 3 Cow milk yield (SEM 1) in Years 3 and 4 under four grassland management systems Grassland management system HH2 Milk yield (kg/day) Year 3 9.5 (0.62) Year 4 7.8ab (0.53)
Fig. 2. Milk yield on the four grassland management systems in Year 3.
3.3. Other parameters Calving interval did not differ (P N 0.05) between the grassland management Systems (Table 2). Pregnancy rates were 0.93, 0.93, 1.00 and 0.93 for Systems HH2, HL2, LL2 and LL1, respectively. 3.4. Milk yield There was no significant difference in milk yield between the grassland management Systems in Year 3 but in Year 4 milk yield was lower (P b 0.01) for HL2 than LL2 or LL1 with HH2 being intermediate (P N 0.05) (Table 3). There was no System × time interaction in Year 3 but in Year 4 there was (P b 0.01), whereby the decline in milk yield as lactation progressed was greater for HL2 than the other three Systems (Figs. 2 and 3). 3.5. Progeny performance Calf liveweight gain from turnout to grass until housing at the end of the grazing season was lower (P b 0.05) for HL2 than HH2 who in turn were lower (P b 0.05) than LL1 whereas calves from System LL2 were intermediate (P N 0.05) to HH2 and LL1 (Table 4). Liveweight gain from turnout to grass until 28 days post-housing was lower (P b 0.01) for HL2 than LL1 with HH2 and LL2 being intermediate (P N 0.05). Calves
Sig.
HL2
LL2
LL1
8.3 (0.62) 6.8a (0.50)
8.6 (0.62) 8.7b (0.46)
9.3 (0.63) 8.7b (0.50)
NS ⁎⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. ab Values with different superscripts differ significantly (P b 0.05). ⁎⁎P b 0.01.
Fig. 3. Milk yield on the four grassland management systems in Year 4.
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Table 4 Calf live weight and live weight gain on the four grassland management systems Grassland management system HH2 Live weight (kg) At birth (16 March) At turnout to grass (20 April) At housing (22 October) 28 days post-housing 13 months (yearling) (8 April)
HL2
LL2
SEM 1
Sig.
LL1
46 77 296a 313 400
45 72 281b 304 396
45 74 299a 314 410
45 74 306a 320 388
1.3 3.5 8.1 8.3 9.5
⁎⁎
Live weight gain (kg) Turnout to grass to housing (186 days) Turnout to grass to 28 days post-housing Housing to 13 months (174 days)
220a 236ab 106a
209b 231a 116b
225ac 239ab 111ab
231c 246b 83c
5.7 5.9 4.5
⁎⁎⁎ ⁎ ⁎⁎⁎
Daily gain (g) Turnout to grass to housing (186 days)
1185a
1128b
1211ac
1256c
27.9
⁎⁎⁎
HH2 — high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests; HL2 — high SR, low N, 2 silage harvests; LL2 — low SR, low N, 2 silage harvests; LL1 — low SR, low N, 1 silage harvest. 1 Standard error of means. abc Values with different superscripts differ significantly (P b 0.05). ⁎P b 0.05, ⁎⁎P b 0.01, ⁎⁎⁎P b 0.001.
from HL2 had a lower (P b 0.05) liveweight at housing than the other three Systems, which did not differ (P N 0.05). However, liveweight recorded four weeks after housing did not differ (P N 0.05) between the four Systems. During the subsequent winter indoor period, liveweight gain of calves from HL2 was higher (P b 0.05) than HH2 with LL2 being intermediate (P N 0.05), whereas calves from LL1 had a lower (P b 0.001) liveweight gain than the other three Systems. At the end of the indoor winter period liveweight did not differ (P = 0.08) between the four Systems. 4. Discussion There is a general need to incorporate findings from component research into beef suckler cow production systems research (Wright et al., 1996; Adams et al., 2000). It is accepted that in systems experiments it is often difficult to replicate treatment groups (Adams et al., 2000; Milne, 2006). Replication of Systems in the present study would have required substantially higher resources. Using grazing experiments in Ireland, Conniffe (1976) found that between-animal–within-herd variation accounted for most of the variation between herds within grazing treatments. Consequently, using the individual animal as the experimental unit should not affect the conclusions drawn. Furthermore, considering the randomization of the experimental area initially and of the cows to the Systems annually and, the fact that this study was carried out over four years, this increases the
likelihood that the results obtained reflect the effects of the management Systems under investigation. 4.1. Grass measurements The pasture heights both pre- and post-grazing were indicative of the stocking rate and fertiliser N levels used in the Systems and the grass growth potential due to soil and environmental conditions. Previous studies with continuous grazing or set-stocked systems have shown that maximum cow and calf performance occurred when sward surface height was maintained at 8 to 10 cm, although to prevent excessive development of reproductive tillers, sward surface heights should be below 8 cm in the first half of the grazing season (Wright et al., 1996). Swards continuously grazed to 4 to 5 cm have resulted in reductions in cow herbage intake, liveweight gain, milk yield and calf liveweight gain (e.g. Wright et al., 1994). The results of the present study indicate, that in a rotationally grazed system, good cow and calf performance were obtained from uncompressed sward post-grazing heights of approximately 7.5 to 9.0 cm (with corresponding pre-grazing heights of approximately 17.5 cm) in the first half of the grazing season (HH2 and LL2 vs. HL2) and post-grazing heights of approximately 6.0 to 6.5 cm (with corresponding pregrazing heights of approximately 12.5 cm) in the second half of the grazing season (HH2, LL2 and LL1 vs. HL2). Drennan et al. (2005b), using a rising plate meter, reported average pre- and post-grazing heights for the
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total grazing season in rotationally grazed systems ranging from 10.9 to 12.6 cm pre and 5.7 to 6.3 cm post, respectively. It is important to note that the sward heights in the present study were uncompressed and would be 1 to 2 cm higher than values obtained with a plate meter at lower sward heights (4 to 6 cm), whereas in taller swards the magnitude of the difference is greater (O'Riordan and O'Kiely, 1996). While herbage samples were not obtained for analyses in the present study, the main differences of magnitude in herbage chemical composition or nutritional value between well-managed, low and high N systems is likely to be crude protein concentrations, reflecting the difference in fertiliser N application (Keane and Allen, 1999; Audic et al., 2002; Drennan et al., 2005b). 4.2. Cow liveweight and body condition score For economic reasons beef suckler cow nutrition on farms involves mobilisation of cow body reserves in winter and subsequent recovery during the grazing season (Petit et al., 1995), the extent depending on herbage supply. The lower BCS gain over the grazing season by cows in System HL2 compared to HH2 and LL2 is consistent with previous studies that have compared the effects of high SR or low herbage allowances with low SR or high herbage allowances (Wright et al., 1994, 1996). The corresponding liveweight gain reflected the BCS gain. Similar to the present findings for Systems HH2 and LL2, Audic et al. (2002) found that decreasing SR by about 0.23 and N fertilisation rate by about 0.63 did not adversely affect the liveweight gain of beef suckler cows on rotationally grazed systems. Although not reflected in cow weight changes, the lower BCS gains on System LL1 during the first half of the grazing season compared to the other three systems may partly be attributed to the high proportion of the total area closed for first-harvest silage and thus, their provision with insufficient grass, which could have negative implications for cow reproductive performance (Drennan and Berry, 2006). Because rumen contents can account for 0.15 to 0.25 of total liveweight gain of beef cows at grass (Agabriel et al., 1993) liveweight gain may not be the best indicator of body reserve deposition at pasture particularly where herbage allowance differs. The lower liveweight and BCS gains of cows on LL2 than LL1 during the second half of the grazing season is probably a reflection of a lower grass supply and additionally, possibly lower quality herbage in the latter part of the year as a result of under-grazing early in the season (Stakelum and Dillon, 1990).
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The high replenishment of body reserves during the total grazing season for Systems HH2, LL2 and LL1 (+ 107 to 119 kg liveweight and +0.73 to 0.98 BCS units) are similar to gains in liveweight and BCS previously obtained at this centre (+ 103 kg live weight and 0.94 BCS units) for rotationally grazed spring-calving beef suckler cows (Drennan and McGee, 2004). 4.3. Milk yield and calf performance The greater decline in milk yield as lactation progressed in Year 4 than Year 3 can be associated with the poor grass growth (Fig. 1) due to a soil moisture deficit in that year and consequently, a lower pasture supply as indicated by the lower pre- and post-grazing sward heights. Similarly, the greater decline in milk yield for HL2 in Year 4 than the other systems reflects the lower grass supply. These results are in accord with Wright and Russel (1987) who found that the persistency of lactation was adversely affected when cows grazed to a lower post-grazing height. The lower milk yield in HL2 compared to HH2 (P = 0.09) and LL2 (P b 0.01) in Year 4 is consistent with previous studies, which have shown that cows on high SR or offered low herbage allowances have lower milk yields [and greater cow liveweight and (or) body condition loss (or lower weight and condition gains)] than cows on lower SR or offered higher herbage allowances and consequently, their calves generally have lower liveweight gains (Drennan, 1971a,b; Baker et al., 1981a,b, 1982; Wright et al., 1994). When feed supply is inadequate, beef suckler cows partition nutrients towards milk production rather than body reserve deposition and thus, milk lessens the adverse impact of feed restriction on the suckling calf (Petit et al., 1995). However, with prolonged undernutrition milk yield will be adversely affected. When milk supply to the calf decreases grass intake usually increases but this substitution is generally insufficient to offset a decline in calf growth resulting from decreased milk production (Wright and Russel, 1987) as was evident in the lighter liveweight at housing of calves from System HL2. This can have important implications for calf-to-beef production as data shows that in springcalving, temperate pasture based-systems, liveweight differences at weaning are largely retained until slaughter (Drennan and McGee, 2004; Drennan et al., 2005a). However, the subsequent absence of a difference between Systems in the post-housing calf weight indicates that some of the weight differences at housing were due to gut-fill differences, which would be expected to be lower for HL2 animals due to limited
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grass supplies. Consequently, the subsequent higher weight gain during the winter period of calves in HL2 than HH2 was likely to be partly attributed to a lower initial weight of gut contents. The lower liveweight gain during the winter period of calves in LL1 can be attributed to a lower nutrient supply from the grass silage as a result of the 14 day delay in harvesting date. Herbage digestibility decline of this magnitude due to delayed harvest date has been reported by Keating and O'Kiely (2000). In agreement with the results for Systems HH2 and LL2, Audic et al. (2002) found that decreasing SR by about 0.23 and nitrogen fertilisation rate by about 0.63 did not adversely affect the liveweight gain of suckling calves on rotationally grazed systems. The liveweight gains of the calves were in excess of 1.1 kg day− 1 over the grazing season. These values are similar to previous reports where grass supply was not limited on spring-calving rotationally grazed, temperate grassland systems (Drennan and McGee, 2004; Audic et al., 2002; Drennan et al., 2005b) although the magnitude can be largely influenced by the milk yield of the dam (McGee et al., 2005). 4.4. Liveweight output and nitrogen balance hectare− 1 The output of weaned calf ha− 1 was 604, 573, 507 and 518 kg for Systems HH2, HL2, LL2 and LL1, respectively. The differences in liveweight of calves weaned ha− 1 between Systems HH2 and LL2 was attributed to differences in SR because individual animal performance was similar. Wright et al. (1996) comparing set-stocking rates of 2.5 and 2.0 cows ha− 1 on perennial ryegrass swards obtained a liveweight of calves weaned ha− 1 of 550 and 456 kg, respectively whereas Wright et al. (1994) comparing contrasting sward heights reported equivalent weights ranging from 348 to 413 kg ha− 1. The output of yearling calf liveweight ha− 1 was 816, 808, 695 658 kg and including annual cow weight gain increased total output to 896, 859, 771 and 727 kg ha− 1, for Systems HH2, HL2, LL2 and LL1, respectively. Surplus N within grassland-based production systems is susceptible to loss to the wider environment. In accord with previous studies (Lawes et al., 2000), only small proportions of the N inputs were converted to animal product i.e. liveweight gain. The purchased N inputs to these Systems were limited to chemical fertiliser and concentrate supplement. Assuming a crude protein content of 140 g kg− 1 in the purchased concentrate, equivalent to 22.4 g N kg− 1, this equated to an intake of 4.1 kg of N per weanling animal.
Combining the chemical fertiliser N applied, the total purchased N input was 227, 154, 138 and 121 kg ha− 1 for Systems HH2, HL2, LL2 and LL1, respectively. Ignoring N sequestered in the soil and assuming a N content of liveweight gain of 28 g kg− 1 (Lawes et al., 2000) the corresponding N removal by the cow and calf was 25, 24, 22 and 20 kg ha− 1 equating to a N surplus of 202, 130, 116 and 101 kg ha− 1 for Systems HH2, HL2, LL2 and LL1, respectively. (This calculation assumes that all the slurry produced from the cows and progeny was returned to the respective systems, and disregards the surplus herbage grazed by non-experimental animals in Years 1 and 2). In accord with previous findings, reducing fertiliser N use can reduce the N surplus in beef systems (Lawes et al., 2000) and consequently, the pollution risk. Richards et al. (2007) found that when compared to high SR–high fertiliser N beef systems, nitrate leaching was significantly lower in low SR–low fertiliser N beef systems. The N-use efficiency (N output input− 1 ha− 1) for Systems HH2, HL2, LL2 and LL1 were 0.11, 0.16, 0.16 and 0.17, respectively. Dieguez Cameroni et al. (2006) reported an apparent N efficiency of 0.13, 0.15 and 0.26 during the grazing period for growing fattening bulls on high N–high SR, moderate N–high SR and zero N–low SR systems, respectively. From a review of the literature Peyraud and Astigarraga (1998) concluded that lowering levels of N fertilisation (with an appropriate reduction in SR) appeared to be an effective means of reducing N losses of ruminants in grazing systems with little or no change in the animals nutrition or in their individual output. Consequently, the main effect was a decrease in animal output per unit land area. 4.5. Additional considerations According to Gibon (2005) there is a greater need to move from the idea of grassland as a resource for animal production to grassland as a complex agro-ecosystem to be managed at a variety of scales of multifunctionality. Reducing fertiliser inputs and SR has the potential to facilitate the restoration of diverse swards (Isselstein, 2005; Isselstein et al., 2005) and it is believed that agrienvironmental schemes will play an increasing role in achieving biodiversity in the future (Isselstein, 2005). Furthermore, participation by beef farmers in environmental schemes such as REPS can be financially attractive (Crosson et al., 2006). In terms of organic N input, assuming that all the slurry produced from the cows and progeny was returned to the respective systems, the low N, low SR Systems were compatible with the Nitrates Directive of the EU (Directive 91/676/
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EEC), which was subsequently introduced and which limits organic N to 170 kg ha− 1. Additionally, System LL1 verges on compatibility with the REPS operated in Ireland to date, where the maximum permissible level of organic (including grazing deposition) N is 170 kg ha− 1 annum− 1 and total (organic plus chemical) N is 260 kg ha− 1 annum− 1. At the stipulated annual organic N loads of 65, 24 and 57 kg for a beef suckler cow, animals 0–1 and 1–2 years old, respectively, the total organic N on the high and low SR systems was 191 and 159 kg ha− 1, in that order. Addition of the chemical fertiliser N applied gave a total N input of 410, 337, 289 and 273 kg ha − 1 for Systems HH2, HL2, LL2 and LL1, respectively. As the vast proportion of liveweight gain on the current systems was obtained from grazed and conserved grass, bringing animals to slaughter on similar grass-based systems may enhance the content of beneficial fatty acids and improve the stability of meat in comparison to alternative systems, such as highconcentrate diets (McGee, 2005; Scollan et al., 2005). 5. Conclusions Increasing the level of fertiliser N application at the high SR or reducing the SR at the low level of N, increased cow liveweight and BCS gain at pasture and prolonged the grazing season. Good cow and calf performance at pasture was obtained in both the high SR and high N, and low SR and low N Systems, indicating a successful substitution of fertiliser N by additional land area. While at low SR, the winter grass silage requirements could be provided in one delayed harvest as opposed to two harvests thereby reducing the conservation area (and associated costs kg− 1 DM), but delayed harvesting of silage resulted in lower digestibility and reduced calf performance in winter. An alternative option for a low SR, low N System may be midway between Systems LL2 and LL1 by having a planned, staggered, one-harvest silage system where the early-harvest provides high digestibility grass silage for the progeny and the later delayed harvest adequate nutritive value silage for the cow, but this needs to be quantified. Such an adjustment would be necessary for the one-harvest System in order to provide an adequate herbage supply early in the grazing season to offset the possible adverse effect on cow reproductive performance. This study indicated the specifications for a lower fertiliser N grassland system, particularly where qualification for EU environmental schemes is dependent on moderate stocking densities.
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Acknowledgements The authors wish to acknowledge the farm staff at Grange Research Centre for care and management of the animals and M. Greally for skilled technical assistance. Also thanks to the staff of Grange Laboratories for grass silage analyses. References Adams, D.C., Nielsen, M.K., Schacht, W.H., Clarke, R.T., 2000. Designing and conducting experiments for range beef cows. Proc. Am. Soc. Anim. Sci. 1999. Agabriel, J., Petit, M., Giraud, J.M., 1993. Rumen contents of Charolais cows during the grazing period. Ann. Zootech. 42, 162. Audic, C., Hardy, A., Pelletier, P., 2002. Extensification of grazed pastures in French suckling cow systems. Grassl. Sci. Europe 7, 1008–1009. Baker, R.D., Alvarez, F., Le Du, Y.L.P., 1981a. The effect of herbage allowance upon the herbage intake and performance of suckler cows and calves. Grass Forage Sci. 36, 189–199. Baker, R.D., Le Du, Y.L.P., Alvarez, F., 1981b. The herbage intake and performance of set-stocked suckler cows and calves. Grass Forage Sci. 36, 201–210. Baker, R.D., Barker, J.M., Le Du, Y.L.P., 1982. The influence of winter nutrition, grazing system and stocking rate on the performance on spring-calving Hereford × Friesian cows and their calves 2. Grazing system and stocking rate. Anim. Prod. 34, 225–237. Conniffe, D., 1976. A comparison of between and within herd variance in grazing experiments. Ir. J. Agric. Res. 15, 39–46. Crosson, P., O'Kiely, P., O'Mara, F.P., Wallace, M., 2006. The development of a mathematical model to investigate Irish beef production systems. Agric. Syst. 89, 349–370. Dieguez Cameroni, F., Hornick, J., Cabaraux, J., Istasse, L., Dufrasne, I., 2006. Less intensified grazing management with growing fattening bulls. Anim. Res. 55, 105–120. Dillon, P., Berry, D.P., Evans, R.D., Buckley, F., Horan, B., 2006. Consequences of genetic selection for increased milk production in European seasonal pasture based systems of milk production. Livest. Sci. 99, 141–158. Drennan, M., 1993. Planned Suckler Beef Production. Teagasc, p. 72. Beef Series No. 4. Drennan, M.J., 1971a. Single-suckled beef production 1. Influence of stocking rate during the grazing season, creep grazing of the calf and double-suckling on live weight changes and milk production of the cows. Ir. J. Agric. Res. 10, 287–295. Drennan, M.J., 1971b. Single-suckled beef production 2. Influence of stocking rate during the grazing season, creep grazing of the calf and double-suckling on calf performance. Ir. J. Agric. Res. 10, 297–305. Drennan, M.J., McGee, M., 2004. Effect of suckler cow genotype and nutrition level during the winter on voluntary intake and performance and on the growth and slaughter characteristics of their progeny. Ir. J. Agric. Food Res. 43, 185–199. Drennan, M.J., Berry, D.P., 2006. Factors affecting body condition score, liveweight and reproductive performance in spring-calving suckler cows. Ir. J. Agric. Food Res. 45, 25–38. Drennan, M.J., McGee, M., Keane, M.G., 2005a. Post-weaning performance and carcass characteristics of steer progeny from different suckler cow breed types. Ir. J. Agric. Food Res. 44, 195–204.
248
M.J. Drennan, M. McGee / Livestock Science 117 (2008) 238–248
Drennan, M.J., McGee, M., Kyne, S., O'Neill, B., 2005b. Spring calving suckler beef systems: influence of grazing system on herbage availability, utilisation, quality and cow and calf performance to weaning. In: O'Mara, F.P., Wilkins, R.J., Mannetje, L.'t, Lovett, D.K., Rogers, P.A.M., Boland, T.M. (Eds.), XX International Grassland Congress: Offered Papers. Wageningen Academic Publishers, The Netherlands, p. 167. Fitzgerald, D.A., Fitzgerald, D.L., 2004. Meteorological measurements. In: Keane, T., Collins, J.F. (Eds.), Climate, Weather and Irish Agriculture. Met Eireann, Dublin, Ireland, pp. 9–26. Gardiner, M.J., 1962. Animal Production Research Centre, Grange, Co. Meath (Soil Map), Soil Survey Bulletin No. 2. An Foras Taluntais, Dublin, Ireland. Gately, T.F., 1994. Soil Analysis and Fertiliser, Lime, Animal Manure and Trace Element Recommendations. Teagasc, Johnstown Castle, Wexford, Ireland, p. 36. Gibon, A., 2005. Managing grassland for production, the environment and the landscape. Challenges at the farm and the landscape level. Livest. Prod. Sci. 96, 11–31. Isselstein, J., 2005. Enhancing the biodiversity and its consequences for grassland management and utilisation. In: McGilloway, D.A. (Ed.), Grassland: a Global Resource. Wageningen Academic Publishers, The Netherlands, pp. 305–320. Isselstein, J., Jeangros, B., Pavlu, V., 2005. Agronomic aspects of biodiversity targeted management of temperate grasslands in Europe — a review. Agron. Res. 3, 139–151. Keane, M.G., Allen, P., 1999. Effects of pasture fertiliser N level on herbage composition, animal performance and on carcass and meat quality traits. Livest. Prod. Sci. 61, 233–244. Keating, T., O'Kiely, P., 2000. Comparison of old permanent grassland, Lolium perenne and Lolium multiflorum swards grown for silage 4. Effects of varying harvesting date. Ir. J. Agric. Food Res. 39, 55–71. Lawes, J.A., Pain, B.F., Jarvis, S.C., Scholefield, D., 2000. Comparison of grassland management systems for beef cattle using self-contained farmlets: effects of contrasting nitrogen inputs and management strategies on nitrogen budgets, and herbage and animal production. Agric. Ecosyst. Environ. 80, 243–254. Lowman, B.G., Scott, N.A., Somerville, S.H., 1976. Condition scoring of cattle. Bulletin, no. 6, (Revised edition). East of Scotland College of Agriculture, p. 31. McGee, M., 2005. Recent developments in feeding beef cattle on grass silage-based diets. In: Park, R.S., Stronge, M.D. (Eds.), Silage Production and Utilisation, Proceedings of the XIVth International Silage Conference (a Satellite Workshop of the XXth International Grassland Congress), July 2005, Belfast, Northern Ireland. Wageningen Academic Publishers, The Netherlands, pp. 51–64. McGee, M., Drennan, M.J., Caffrey, P.J., 2005. Effect of suckler cow genotype on milk yield and pre-weaning calf performance. Irish J. Agric. Food Res. 44, 185–194.
Milne, J.A., 2006. Editorial. Grass Forage Sci. 61, 1. O'Kiely, P., Moloney, A.P., Killen, L., Shannon, A., 1997. A computer program to calculate the cost of providing ruminants with homeproduced feedstuffs. Comput. Electron. Agric. 19, 23–36. O'Riordan, E.G., 1997. Effect of annual application rate and grass growth interval on annual herbage production. Proc. Agric. Res. Forum, Belfield, Dublin, 3rd and 4th April, pp. 133–134. O'Riordan, E.G., O'Kiely, P., 1996. Potential of beef production systems based on grass. Ir. Grassl. Anim. Prod. Assoc. J. 30, 185–217. Petit, M., Garel, J.P., D'Hour, P., Agabriel, J., 1995. The use of forages by the beef cow herd. In: Journet, M., Grenet, E., Farce, M.-H., Theriez, M., Demarquilly, C. (Eds.), Recent Developments in the Nutrition of Herbivores. Proceedings of the IVth International Symposium on the Nutrition of Herbivores. INRA, Editions, Paris, pp. 473–496. Peyraud, J.L., Astigarraga, L., 1998. Review of the effect of nitrogen fertilization on the chemical composition, intake, digestion and nutritive value of fresh herbage: consequences on animal nutrition and N balance. Anim. Feed Sci. Technol. 72, 235–259. Richards, K., Drennan, M., Lenehan, J.J., Connolly, J., Brophy, C., Carton, O.T., 2007. Nitrate leaching from Irish beef farming, a look at the impact of REPS. Proc. Agric. Res. Forum. Teagasc, Tullamore, Ireland, p. 3. Scollan, N.D., Dewhurst, R.J., Moloney, A.P., Murphy, J.J., 2005. Improving the quality of products from grassland. In: McGilloway, D.A. (Ed.), Grassland: a Global Resource. Wageningen Academic Publishers, The Netherlands, pp. 41–56. Stakelum, G., Dillon, P., 1990. Influence of sward structure and digestibility on intake and performance of lactating and growing cattle. In: Mayne, C.S. (Ed.), Management Issues for the Grassland Farmer in the 1990s, Br. Grassl. Soc., Occasional. Pub. No. 25, pp. 30–42. Statistical Analysis Systems Institute, 2003. SAS/STAT. The SAS System for Windows, Release 9.3.1. SAS Institute Inc., Cary, NC, USA. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104–111. Wright, I.A., Russel, A.J.F., 1987. The effect of sward height on beef cow performance and on the relationship between calf milk and herbage intakes. Anim. Prod. 44, 363–370. Wright, I.A., Jones, J.R., Maxwell, T.J., Russel, A.J.F., Hunter, E.A., 1994. The effect of genotype × environment interactions on biological efficiency in beef cows. Anim. Prod. 58, 197–207. Wright, I.A., Maxwell, T.J., Russel, A.J.F., Hunter, E.A., Hetherington, R.A., Whyte, T.K., 1996. The effect of grazed sward height and stocking rate on animal performance and output from beef cow systems. Grass Forage Sci. 51, 199–208.