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The effect of quality of grass and maize silage on the intake and performance of beef cattle
Livestock Science 100 (2006) 179 – 188 www.elsevier.com/locate/livsci
The effect of quality of grass and maize silage on the intake and performance of beef cattle R.M. Kirkland *, D.C. Patterson 1 The Agricultural Research Institute of Northern Ireland, Hillsborough, Co. Down, Northern Ireland BT26 6DR, UK Received 11 April 2005; received in revised form 9 August 2005; accepted 24 August 2005
Abstract A study was undertaken to evaluate the effects of incorporating high (HMS) and low (LMS) maturity maize silages into diets based on low (LGS) and high (HGS) feed value grass silages offered to beef cattle. Seventy-two continental cross-bred steers were used in a 14-week continuous design, randomised block experiment. The six treatments were arranged as a 2 3 factorial design incorporating the LGS and HGS offered as the sole forage, along with each of the two grass silages offered in a 60:40 ratio (DM basis) with the HMS and LMS. All diets were supplemented with 3 kg/head/day concentrates. Total daily DM and metabolisable energy intakes were higher ( P b 0.001) for diets based on HGS compared to those based on LGS. Intakes were similar ( P N 0.05) between diets containing LMS and HMS, both of which were higher ( P b 0.001) than diets containing grass silage as the sole forage. Highest DM intakes were recorded with a mixture of HGS and HMS ( P b 0.05 or greater). Cattle offered diets containing HGS had higher live-weight gain ( P b 0.05), final live weight, carcass gain and carcass weight ( P b 0.001) than those offered diets containing LGS. Feed conversion efficiency, assessed on a carcass gain basis, was poorer ( P b 0.05) with diets containing LGS compared with those containing HGS, though differences between diets containing either LMS or HMS and GS as the sole forage were not significant ( P N 0.05). D 2005 Elsevier B.V. All rights reserved. Keywords: Grass silage; Maize silage; Intake; Beef cattle; Animal performance
1. Introduction The development of early maturing maize varieties, and the introduction of the complete cover * Corresponding author. Tel.: +44 28 9268 2484; fax: +44 28 9268 9594. E-mail address: [email protected] (R.M. Kirkland). 1 Also a member of The Queen’s University of Belfast, Belfast, Northern Ireland BT9 5PX, and the Department of Agriculture and Rural Development for Northern Ireland. 0301-6226/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.08.015
plastic mulch system of maize production, has considerably improved the potential and viability of maize as an alternative forage for use in ruminant production systems in areas of the UK and Western Europe which are climatically marginal for growing maize (Keady, 2003). Furthermore, recent estimates indicate that production costs of maize silage (MS) can be competitive with those of grazed grass and grass silage (GS) (Keady et al., 2002b).
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A number of studies have reported positive effects on feed intakes when forage MS replaced GS either totally or as part of the forage base for beef cattle (McCabe et al., 1995; Browne et al., 2000; O’Kiely and Moloney, 2000; Keady and Kilpatrick, 2004) and dairy cows (Keady et al., 2002a, 2003). However, improvements in forage intake, observed in many studies, have not consistently resulted in improved levels of animal performance (O’Kiely and Moloney, 2000) such that the production, and ultimately financial, implications of incorporating MS into the diet of beef cattle is not clear. Furthermore, few studies have examined the effects of offering diets incorporating GS and MS of differing qualities on the performance of beef cattle. Given the suitability of the climate in many areas of Western Europe for the production of high yielding crops of GS, it is likely that GS will remain the predominant forage in areas more marginal for maize production. However, given the variability in the quality of forage produced (Steen et al., 1998; Easson, 2000), it is important to evaluate the effects on animal production of incorporating MS differing in nutritive value into GS-based diets. The objective of the present study was to examine the effects on forage intake, animal performance and carcass characteristics of including MS, harvested at different stages of maturity, as a component of GSbased diets, in comparison to GS of differing feed value offered as the sole forage.
2. Materials and methods 2.1. Preparation of silages All silages were prepared from material harvested throughout the 2001 season. Two grass silages differing in feed value were harvested using precision chop forage harvesters and ensiled in clamp silos. The high feed value GS (HGS) was ensiled from primary growth herbage of a perennial ryegrass dominant sward between the 18 and 22 May, following a 36-h wilt, and treated with an additive (Ecosyl; Ecosyl Products Ltd., Middlesborough, UK). The low feed value GS (LGS) was ensiled from the second regrowth of a perennial ryegrass dominant sward on
the 20–21 September (without additive) following a 30-h wilt. High-maturity maize silage (HMS) was harvested in late October from the early variety Passat, while low-maturity MS (LMS) was harvested in early November from the later maturing variety Loft. Both MS were precision chopped, treated with additive (Ecocorn; Ecosyl Products Ltd., Middlesborough, UK) and ensiled in clamp silos. 2.2. Animals and experimental design Seventy-two continental cross-bred steers (mean initial live weight 485 kg; S.D. 24.0) were used in a 14-week continuous design, randomised block experiment. Animals were blocked into groups of six animals according to similarity of live weight, and one animal from each block allocated at random to one of six dietary treatments, giving 12 observations per treatment. The treatments were arranged as a 2 3 factorial design incorporating 2 GS (HGS and LGS) and 3 MS (HMS, LMS and no MS). The six dietary treatments comprised the 2 GS offered as the sole forage, along with each of the two GS offered in a 60:40 ratio (GS/MS on a dry matter [DM] basis) with both HMS and LMS. The silage mixtures were blended and offered once daily through individual Calan Broadbent gates. The quantity of each forage in the mix was determined daily based on the mean DM concentration of the forages over the previous 3 days. All forages were offered ad libitum to enable a 50 to 100 g/kg refusal. The quantities of forage offered to, and refused by, each individual animal were recorded daily, and uneaten material discarded on a daily basis. All diets were supplemented with 3 kg/head/day concentrates which were presented in the food box once daily on top of the forage mixture. Concentrate was formulated such that the crude protein (CP) concentration of the diet with the lowest determined CP concentration was 140 g/kg DM. The concentrate consisted of the following ingredients (g/ kg fresh weight): barley (425), soya bean meal (250), molassed sugarbeet pulp (150), maize meal (150) and mineral supplement (25). 2.3. Measurements Animals were weighed on 2 consecutive days at the beginning of each of the first 3 weeks of the study,
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at weekly intervals thereafter, and on 2 consecutive days prior to slaughter. Live weight gain of each animal was calculated by linear regression of live weight against time (days). Estimated rate of carcass gain was calculated by assuming an initial carcass weight for all animals of 0.52 of initial live weight, which was determined from similar animals in previous studies at this Institute (Keady, 1991). Following slaughter, all carcasses were graded visually for conformation and fatness using the five point scale of the European Carcass Classification Scheme (Kempster et al., 1982). The depth of subcutaneous fat over the eye muscle (m. longissimus dorsi) was measured at points a quarter, half and three-quarters way across the width of the eye-muscle at the 10th rib on both sides of each carcass. The amount of marbling fat in the cut surface of the eye-muscle was assessed independently by two individuals using the eight-point scale of the United States Department of Agriculture photographic standards (Agricultural Research Council, 1965). A photograph was taken of the cut surface of the eye-muscle at the 10th rib on both sides of each carcass and the area of each determined using a DeltaT Devices leaf-area machine. Weights of kidney, cod and channel fat, removed during the dressing procedure of each carcass, were recorded from each animal. After chilling, the fore-rib joint was removed from the left side of each carcass as described by Kempster et al. (1980) and was fully dissected into separable lean, separable fat and bone using the method described by Cuthbertson et al. (1972). 2.4. Digestibility studies and sample analyses Silage DM concentration was determined daily by drying at 85 8C, and the daily dried samples were bulked weekly for determination of acid detergent fibre (ADF), neutral detergent fibre (NDF) and ash. Further fresh silage samples were taken once weekly throughout the study and analysed for volatile corrected oven dry matter (VCODM) concentration, pH, nitrogen (N), NH3–N (proportion of total N), lactic acid, volatile fatty acids and alcohol concentrations and gross energy (GE). A representative sample of forage refusal for each treatment was analysed daily for oven DM concentration. Concentrates were sampled daily and bulked weekly for determination of DM, N, ash, ADF and NDF concentrations. Che-
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mical analyses were undertaken as described by Keady et al. (1998, 1999). The digestibilities of the six diets were determined through six cattle of similar live weight in a fourperiod, partially balanced, changeover design experiment, giving a total of four observations per diet, with all forages being offered ad libitum. Each period consisted of a 15-day feed-in period followed by a 6-day collection period of faeces and urine. The procedures for the determination of digestibility were similar to those described by Steen (1984), with feed and faecal samples being bulked for 3day periods and analysed for DM, organic matter (OM), N, ADF, NDF and GE concentrations. The DM concentration of each forage was determined daily while further silage samples were dried at 65 8C and bulked over 3-day periods for determination of water-soluble carbohydrate (WSC) and starch concentrations. The concentration of metabolisable energy (ME) of the total diets was determined by assuming that methane production was 0.07 of the GE intake. 2.5. Statistical analysis Data on the chemical composition of the forages offered were analysed by Analysis of Variance using Genstat 5 (Lawes Agricultural Trust, 1998). Data on food intake, animal performance and carcass characteristics were analysed using a two-way analysis of variance technique with forage type (GS or MS) as the main factor. For each individual factor analysed, live weight at the start of the study was incorporated into the analyses as a covariate. Data on total diet digestibility and concentration of ME were analysed using the REML technique in Genstat 5 with forage type (GS or MS) as the main factor.
3. Results 3.1. Grass silages The chemical compositions of the grass silages are presented in Table 1. Concentrations of DM, CP and lactic acid were lower ( P b 0.01 or greater), and concentrations of NH3–N (proportion of total N), propanol, acetic acid, ash, ADF and NDF higher ( P b 0.05
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Table 1 Chemical composition of the grass silagesa Grass silagesb LGS DM (g/kg) 251 pH 3.9 NH3–N (prop. total N) 0.10 Intake valued 74 Composition of DM (g/kg unless CP 131 Ethanol 11.8 Propanol 6.5 Acetic acid 27.9 Butyric acid 5.7 Propionic acid 1.4 Valeric acid 0.04 Lactic acid 82.8 Ash 97 ADF 313 NDF 538 WSC 8 GE (MJ/kg DM) 18.90
SED
Significancec
HGS 304 3.9 0.08 91 otherwise 152 11.6 0.8 17.2 2.5 0.9 0.09 112.5 83 300 502 41 18.77
8.0 0.06 0.004
*** NS ***
stated) 5.6 2.06 1.51 2.46 1.67 0.32 0.032 10.77 2.2 5.6 7.8 16.7 0.507
*** NS *** *** NS NS NS ** *** * *** NS NS
a DM, dry matter; CP, crude protein; ADF, acid detergent fibre; NDF, neutral detergent fibre; WSC, water-soluble carbohydrates; GE, gross energy. b LGS, low feed value grass silage; HGS, high feed value grass silage. c NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. d Predicted intake value from Hillsborough Feeding Information System (g DM/kg live weight0.75 ).
The chemical composition of the concentrate offered throughout the study was DM 838 g/kg, CP 198, ADF 84, NDF 187, ash 66 and predicted starch (using published values) 313 g/kg DM, and GE 17.9 MJ/kg DM. 3.3. Total diet digestibility and ME and CP concentrations Digestibility and CP and ME concentrations of the total diets are presented in Table 3. Diets based on HGS had higher ( P b 0.001) DM, OM, GE, ADF and NDF digestibilities, as well as N digestibility ( P b 0.05). Concentration of ME was also higher ( P b 0.05 or greater) for diets based on HGS (12.10 MJ/kg DM) compared to those based on LGS (11.66 MJ/kg DM). Digestibility of DM, OM, GE and N was similar ( P N 0.05) between diets containing LMS and HMS and those containing no MS (GS offered as the sole forage), whilst diets containing GS as the sole for-
Table 2 Chemical composition of the maize silagesa Maize silagesb LMS
or greater) in LGS compared to HGS. Silage type had no effect ( P N 0.05) on pH or concentrations of ethanol, butyric acid, propionic acid, valeric acid, WSC and GE. Silage intake potential (g DM/kg live weight0.75), predicted using the Hillsborough Feeding Information System (Steen et al., 1998), was 74 and 91 for the LGS and HGS, respectively. 3.2. Maize silages The chemical composition of the MS are presented in Table 2. Concentrations of DM and starch were lower ( P b 0.001), and concentrations of CP, ethanol, propanol, acetic acid, propionic acid, lactic acid, ADF, NDF and GE were higher ( P b 0.05 or greater) in LMS compared to HMS. Silage type had no effect ( P N 0.05) on pH, or concentrations of NH3–N (proportion of total N), butyric acid, valeric acid, ash and WSC.
SED
Significancec
HMS
DM (g/kg) 246 394 12.2 *** pH 3.9 4.0 0.04 NS NH3–N (prop. total N) 0.09 0.08 0.005 NS Composition of VCODM (g/kg unless otherwise stated) CP 80 75 0.2 *** Ethanol 9.4 4.3 1.36 *** Propanol 4.4 1.8 0.93 ** Acetic acid 32.8 12.9 2.13 *** Butyric acid 0.5 0.7 0.18 NS Propionic acid 1.3 0.5 0.36 * Valeric acid 0.0 0.0 0.00 NS Lactic acid 58.0 40.8 5.17 ** Ash 53 51 3.4 NS ADF 327 258 8.2 *** NDF 600 515 8.6 *** WSC 6.4 6.2 0.74 NS Starch 122 280 9.1 *** GE (MJ/kg DM) 18.88 18.31 0.203 ** a DM, dry matter; CP, crude protein; ADF, acid detergent fibre; NDF, neutral detergent fibre; WSC, water-soluble carbohydrates; GE, gross energy. b LMS, low-maturity maize silage; HMS, high-maturity maize silage. c NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001.
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Table 3 Digestibility and crude protein (CP) and metabolisable energy (ME) concentrations of the total diets Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
0.727 0.754 0.723 0.629 0.692 0.684 147.6 11.51
0.781 0.802 0.766 0.714 0.750 0.752 160.8 12.23
0.732 0.756 0.729 0.608 0.681 0.684 131.5 11.70
0.742 0.762 0.737 0.616 0.666 0.667 130.8 11.76
0.769 0.787 0.758 0.672 0.724 0.722 139.8 12.12
0.775 0.792 0.760 0.675 0.721 0.718 137.7 11.95
Digestibility coefficientsb DM OM GE N ADF NDF CP (g/kg DM) ME (MJ/kg DM)
SED
Grass
Maize
Grass Maize
0.0072 0.0072 0.0077 0.0395 0.0122 0.0119 4.93 0.267
*** *** *** * *** *** ** *
NS NS NS NS ** * *** NS
*** *** *** * *** *** *** *
NS, non-significant; *P b 0.05; **P b 0.01; *** P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage. b DM, dry matter; OM, organic matter; GE, gross energy; N, nitrogen; ADF, acid detergent fibre; NDF, neutral detergent fibre; ME, metabolisable energy.
age had higher ( P b 0.05) ADF and NDF digestibility (0.721 and 0.718, respectively) than those containing HMS (0.694 and 0.693, respectively). Dietary ME concentration was similar ( P N 0.05) between diets containing LMS, HMS and no MS. There were also significant interactions between diets based on each GS and MS in that digestibility of DM, OM and GE was lower ( P b 0.01 or greater) for diets containing LGS, or those containing LGS with either LMS or HMS, than those containing HGS (either as the sole forage or in combination with LMS or HMS). Digestibility of dietary N was higher ( P b 0.05) for diets containing HGS as the sole forage compared to diets containing forage mixtures of LGS and either LMS or HMS. Digestibility of ADF and NDF was higher ( P b 0.05 or greater) for diets containing HGS as the sole forage compared to all other diets (the only exception being the similar ( P N 0.05) ADF digestibility recorded between diets containing HGS as the sole forage and the HGS-LMS forage mixture). Forage mixtures containing HGS had higher ( P b 0.05 or greater) ADF and NDF digestibilities than diets containing LGS either as the sole forage or in combination with either LMS or HMS. Diets containing LGS as the sole forage had the lowest ME concentration, significantly ( P b 0.05) below diets containing HGS as the sole forage and diets containing the HGS-LMS forage mixture. Concentration of CP was highest ( P b 0.05 or greater) for diets containing HGS as the sole forage.
3.4. Food intake, animal performance and carcass data Data on food intake and animal performance are presented in Table 4. Total daily DM and ME intakes were greatest for diets based on HGS (9.39 kg/day and 113.6 MJ/day, respectively) compared to those based on LGS (8.38 kg/day and 97.7 MJ/day, respectively) ( P b 0.001). Dry matter and ME intakes were similar ( P N 0.05) between diets containing LMS (9.07 kg/ day and 108.1 MJ/day, respectively) and HMS (9.22 kg/day and 109.4 MJ/day, respectively), both of which were higher ( P b 0.001) than diets containing GS as the sole forage (8.37 kg/day and 99.5 MJ/day, respectively). Diets containing a mixture of HGS and HMS promoted higher ( P b 0.05 or greater) DM intakes than all other diets, whilst intakes of diets containing LGS as the sole forage were significantly lower ( P b 0.01 or greater) than all other diets. Cattle offered diets containing HGS had higher live-weight gain (1187 g/day) ( P b 0.05), final live weight (599 kg), estimated rate of carcass gain (857 g/day) and carcass weight (327 kg) ( P b 0.001) than those offered diets containing LGS (1050 g/day, 574 kg, 699 g/day and 310 kg, respectively). Feed conversion efficiency, assessed on a live-weight gain basis, was not influenced by type of forage offered in the diet ( P N 0.05). In contrast, feed conversion efficiency for carcass gain (DM basis) was poorer ( P b 0.05) with diets containing LGS (12.1 kg DM/ kg carcass gain) compared to those containing HGS
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Table 4 Effect of grass silage quality and inclusion of maize silage on food intake and animal performance Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
Total DM intake (kg/day) Total ME intake (MJ/day) Animal performance data Live-weight gain (g/day) Live weight at slaughter (kg) DMI/live-weight gain (kg/kg) Live-weight gain/MEI (g/MJ) Carcass gain (g/day) Carcass weight (kg) DMI/carcass gain (kg/kg) Carcass gain/MEI (g/MJ)
7.72 88.8
9.02 110.3
981 570 8.4 10.6 699 310 11.4 7.8
1166 596 7.8 10.5 808 325 11.0 7.6
8.90 104.1 1134 580 8.2 10.8 715 312 12.3 6.8
8.51 100.2 1037 573 8.5 10.2 683 308 12.5 6.7
9.25 112.1 1247 602 7.6 10.9 907 329 10.3 8.0
9.92 118.6 1147 600 8.1 10.4 858 327 12.0 7.1
SED
0.276 3.28 92.3 9.4 0.60 0.72 51.3 4.8 0.66 0.47
Grass
Maize
Grass Maize
*** ***
*** ***
*** ***
* *** NS NS *** *** * NS
NS NS NS NS NS NS NS NS
NS NS NS NS NS NS NS NS
NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage.
(11.1 kg DM/kg carcass gain), though differences between diets containing either LMS or HMS, and GS as the sole forage, fell just outside the accepted level of significance ( P = 0.054). Diet offered had no effect ( P N 0.05) on the efficiency of carcass gain per unit of MEI. Data on carcass characteristics are presented in Table 5. Forage type offered had no significant influence ( P N 0.05) on dressing proportion, carcass conformation or marbling score. In contrast, mean carcass fat class scores from animals offered diets containing
HGS (either as the sole forage or as a component of the total forage) were numerically, and in most instances significantly, higher than those offered diets containing LGS (up to P b 0.01) (treatment means of 3.3 and 2.8 for cattle offered diets containing HGS and LGS, respectively), while inclusion of MS did not influence this parameter ( P N 0.05). Similarly, subcutaneous fat depth and weight of internal fat depots were higher (at least P b 0.01) from carcasses of animals offered diets containing HGS (5.9 mm and 12.3 kg, respectively) compared to those offered LGS
Table 5 Effect of grass silage quality and inclusion of maize silage on carcass characteristics Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
546
546
532
534
544
539
Dressing proportion (g carcass per kg live weight) Carcass fat classb Carcass conformationc Depth of subcutaneous fat (mm) Marbling scored Internal fat depots (kg)e Area of longissimus dorsi (cm2) Composition of fore-rib joint (g/kg) Separable lean Separable fat Bone
2.5 2.8 3.5 2.4 8.4 70.8 633 160 192
3.4 2.6 6.5 2.8 12.5 66.8 580 245 175
2.9 2.5 3.9 2.8 11.1 66.8 632 188 180
3.1 2.5 5.0 2.6 11.0 64.9 626 184 183
3.2 2.7 5.2 2.5 12.1 70.4 639 187 167
3.2 2.6 6.1 2.4 12.2 72.8 598 216 177
Grass
Maize
Grass Maize
6.8
NS
NS
NS
0.23 0.14 0.70 0.22 0.83 3.07
** NS *** NS *** NS
NS NS NS NS NS NS
* NS NS NS * *
*** *** *
** * NS
** *** NS
SED
11.8 10.6 7.5
NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage. b 5-point scale: 1 = leanest; 5 = fattest. c 5-point scale: 1 = worst; 5 = best. d 8-point scale: 1 = low marbling; 8 = high marbling. e Sum of kidney, cod and channel fats.
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(4.1 mm and 10.2 kg, respectively). Area of m. longissimus dorsi was similar across GS and MS treatments (main effects) ( P N 0.05), but was lower ( P b 0.05) in carcasses from animals offered a forage mixture comprising LGS-HMS compared with those offered the HGS-HMS forage mixture. Analysis of data from dissection of the fore-rib joint showed that animals offered diets containing HGS had higher ( P b 0.001) separable fat and lower separable lean contents than those offered diets containing LGS. Similarly, mean separable fat contents were numerically, and in some instances significantly higher ( P b 0.05), and separable lean contents lower ( P b 0.01), in the fore-ribs of animals offered diets containing GS as the sole forage compared with those offered diets containing MS as a proportion of the forage component.
4. Discussion Data on the effects of maize silage inclusion in grass silage-based diets, assessed in terms of feed intake and animal performance, are necessary to provide a sound scientific basis on which to base nutritional feeding programmes for those involved in beef production. The objective of comparing silages of differing feeding value was achieved, with LGS having lower DM concentration, intake value and poorer fermentation characteristics than HGS. Similarly, LMS and HMS exhibited major differences when assessed in terms of DM, NDF and starch concentrations. 4.1. Digestibility of diets and ME and CP concentration Quality of GS was the main determinant of total diet digestibility recorded in the study, with diets containing HGS (either as the sole forage or in combination with MS) having higher digestibility coefficients (numerically and/or statistically) than other diets across all parameters assessed, primarily reflecting the early harvest date of the herbage from which HGS was produced. However, fibre digestibility tended to be lower with diets containing HMS compared to diets containing LMS, and was significantly lower compared to diets containing GS offered as the sole forage. Similarly, Cammell et al. (2000) reported
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a trend (non-significant) of reducing fibre digestibility when maize of increasing maturity (DM concentrations ranging from 226 up to 357 g/kg) was incorporated into a high-quality GS-based diet for dairy cows, albeit at a much higher rate (3:1 mixture of MS/GS on a DM basis), and incorporating higher rates of concentrate supplementation (8.7 kg DM/day), than that offered in the present study. Significant reductions in MS fibre digestibility with increasing maturity were also reported by Browne et al. (1999), when MS was offered as the sole forage to beef cattle (MS DM concentrations ranging from 273 to 314 to 367 g/kg) and in the study by Andrae et al. (2001). Nevertheless, differences in fibre digestibility recorded between diets containing LMS, HMS and no MS in the present study were not of sufficient magnitude to influence the overall digestibility of the DM component of the respective diets, all of which were similar. Whilst ME concentration of diets based on HGS (mean 12.10 MJ/kg DM) was significantly higher than those based on LGS (mean 11.66 MJ/kg DM), dietary ME concentration was similar between diets containing GS as the sole forage and those containing either of the two MS. This observation is in line with that of Cammell et al. (2000), who reported only marginal (non-significant) declines in dietary ME concentration across the range of MS maturities offered in their study, despite DM and starch concentrations of the most mature MS (357 g/kg and 401 g/kg DM, respectively) being greater than the higher maturity MS (HMS) in the present study. The present data indicate a marginally beneficial effect on dietary ME concentration of incorporating low-maturity MS into a diet based on poor-quality GS, although at the other extreme, ME concentrations tended to be reduced when MS was included in the diet, relative to diets containing HGS offered as the sole forage. While the diets offered in the present study were not formulated to be isonitrogenous, a key objective of the study was to ensure that intake and performance parameters of the cattle were not limited due to insufficient availability of N. Although total diet CP concentration ranged from 130.8 g/kg DM to 160.8 g/kg DM, it is unlikely that animal intake and performance characteristics were influenced by these differences, with Steen (1996) reporting no significant effects on food intake or performance characteristics of beef animals with diets in which the CP concentration
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ranged from approximately 130 g/kg DM to over 200 g/kg DM.
maize inclusion is not specifically a DM effect; therefore, the higher intake must be related to some other characteristic of ensiled forage maize.
4.2. Total diet DM and ME intake 4.3. Animal performance and carcass data Incorporating MS into the diets in the present study resulted in a significant ( P b 0.001) improvement in DM and ME intakes when compared to GS offered as the sole forage (means of 8.37 kg/day and 99.5 MJ/ day, 9.07 kg/day and 108.1 MJ/day, and 9.22 kg/day and 109.4 MJ/day for diets based on GS as the sole forage and those containing LMS and HMS, respectively). Improvements in intakes with inclusion of MS in GS-based diets have been demonstrated in previous studies with beef cattle (Browne et al., 2000; O’Kiely and Moloney, 2000) and with dairy cows (Phipps et al., 1995, 2000; O’Mara et al., 1998; Keady et al., 2002a, 2003). When analysed across individual treatments, the results from the present study demonstrate the potential to increase intakes of diets based on low-quality GS by substituting a proportion of the GS with MS of low or high maturity. The results also indicate the intake promoting effects of MS when included as part of a diet based on a high-quality GS. In the latter example, significant improvements in intakes were recorded when HMS was included in the diet, whilst the trend for higher intakes (relative to GS as the sole forage) with inclusion of LMS is in line with the higher intakes by beef cattle reported by O’Kiely and Moloney (1995) when a high-quality GS was partially replaced by MS of low maturity (205 g/kg DM, 0 g/kg DM starch). Although there is a paucity of studies in the literature which have compared both GS and MS of differing qualities in a single trial as was the case presently, Weller and Phipps (1986) and Phipps et al. (1992) reported improvements in DM intakes (with dairy cows) when MS was included as a component of a forage mixture based on GS of dlowT or dhighT quality. Furthermore, in line with the results of Phipps et al. (1992) from studies with dairy cows, the improvements in forage intakes with the mixed forage diets observed presently (relative to GS offered as the sole forage) were obtained without any significant effects on DM digestibility, indicating that this factor was not the major driving force promoting the higher intakes. There is also evidence from the present study that the improvement in intake with forage
Interactions between GS and MS treatments were absent for the majority of the animal performance traits measured in this study, though significant differences were recorded between main effects. Animals offered diets based on HGS had higher levels of performance across a number of the parameters assessed, while inclusion of MS in the diets generally had no significant influence on the level of performance obtained relative to that achieved where GS was offered as the sole forage. The significantly higher rates of live weight and carcass gains recorded with animals offered diets based on HGS compared with those of cattle offered diets based on LGS, generated 24.8 kg heavier live weight at slaughter and 16.7 kg heavier carcass weight. Despite these increases in animal weight parameters recorded, feed efficiency assessed on a liveweight gain basis was similar across all dietary treatments imposed. In contrast, differences in treatment means reached significance when assessed as kg DMI per kg carcass gain, feed efficiency being poorer (8.6% poorer) with animals offered diets based on LGS compared to those offered diets based on HGS. This difference derived from the 12.1% higher mean DMI achieved with the latter diet types compared with that of the former diet types, and the greater magnitude of the corresponding improvement in mean rate of carcass gain of 22.6%. However, inclusion of HMS in the diet, despite improving mean DMI by 10.2% relative to diets containing GS as the sole forage, resulted in only a marginal improvement in rate of carcass gain of 2.3%. These data concur with results from other studies reported in the literature, where improvements in food intake with inclusion of MS in GS-based diets have not resulted in concomitant improvements in rates of gain (O’Kiely and Moloney, 2000). Breen and Keane (2000) observed similar levels of beef animal performance when a mediumquality GS was partially replaced with a MS of very low maturity (192 g/kg DM, 27 g/kg DM starch), much lower than the maturity of either MS offered in the present study. These data indicate that inclusion
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of MS in the diet (even when of low quality) can give similar levels of animal performance relative to that of animals offered GS as the sole forage. Inclusion of MS in the diet had no significant influence on any of the main carcass parameters assessed in the study. These findings concur with results reported by other authors from studies in which MS was incorporated into a GS-based diet (McCabe et al., 1995; Breen and Keane, 2000). However, Browne et al. (2000) reported improved kill-out proportions, while O’Kiely and Moloney (2000) reported increased carcass fat class scores (numerically or significantly) of beef cattle offered diets containing MS compared to diets containing GS as the sole forage. Taken together, these data suggest that inclusion of MS in a GS-based diet, even when incorporated at rates up to 100% of the forage component of the diet, has no major or consistent effects on the main carcass characteristics. In a review of the influence of MS inclusion in the diet, Keady (2003) concluded that the doptimalT stage of maturity to harvest MS for dairy cows, based on fat plus protein yield, is approximately 300 g/kg DM. Given the DM concentration of the LMS (246 g/kg DM) and HMS (394 g/kg DM) in the present study, and the associated differences in other nutritional parameters, it is postulated that the absence of responses in animal performance to addition of MS to diets observed presently might reflect to some degree the disparity of these figures from the value quoted by Keady (2003) as doptimalT for dairy cow performance. In contrast to the data recorded with inclusion of MS in diets, quality of GS offered resulted in differences in carcass fat characteristics, with carcasses from animals offered diets containing HGS having higher fat class scores, subcutaneous fat depths, and greater mass of internal fat depots. It was initially postulated that these differences might reflect the higher growth rates and subsequent higher slaughter weights achieved by animals offered diets containing HGS compared to those offered diets containing LGS. Steen and Kilpatrick (1995) reported significant reductions in carcass fat characteristics when slaughter weights of bulls, steers and heifers were reduced by restricting intakes compared to animals offered feed ad libitum. However, re-analyses of the data in the present study after correction to constant carcass
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weight had no appreciable influence on carcass fat parameters, the covariate having no significant effect ( P N 0.05) on any of the measured variables. However, in contrast to the present data, Thomas et al. (1988) and Steen (1992) reported no effect on carcass fat characteristics when cattle were offered high compared to low digestibility GS, despite major differences in rates of carcass gain between the diets. If differences in carcass weight are not the major factor influencing the higher fat characteristics of animals offered diets containing HGS, it is probable that these differences at least partly reflect the higher ME intake and forage/concentrate ratio (and hence, increased acetate/propionate ratio) resulting from the improved forage intakes associated with animals offered diets containing HGS. Work by Beever et al. (1992) has suggested that a higher proportion of acetate in the rumen promotes greater synthesis of body fat.
5. Conclusions The results of the present study indicate that inclusion of MS in GS-based diets can improve DM intakes when offered to finishing beef cattle. However, the absence of improvements in feed efficiency and animal performance by incorporation of MS into the diet, relative to GS offered as the sole forage, probably reflects the extremes of maturity of the MS offered.
References Agricultural Research Council, 1965. Recommended Procedures for Use in the Measurement of Beef Cattle and Carcasses. Agricultural Research Council, London. Andrae, J.G., Hunt, C.W., Pritchard, G.T., Kennington, L.R., Harrison, J.H., Kezar, W., Mahanna, W., 2001. Effect of hybrid, maturity, and mechanical processing of corn silage on intake and digestibility by beef cattle. J. Anim. Sci. 79, 2268 – 2275. Beever, D.E., Dawson, J.M., Buttery, P.J., 1992. Control of fat and lean deposition in forage-fed cattle. In: Buttery, P.J., Boorman, K.N., Lindsay, D.B. (Eds.), The Control of Fat and Lean Deposition. Heinemann, Butterworth, pp. 211 – 229. Breen, J., Keane, G.P., 2000. Aspects of feeding maize silage to beef cattle. Summary of Papers Presented at the Agricultural Research Forum, Faculty of Agriculture, University College Dublin, Belfield, Dublin, pp. 177 – 178.
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Browne, E.M., Bryant, M.J., Beever, D.E., 1999. Apparent digestibility and nitrogen utilization of maize silage harvested at three stages of maturity and fed to beef cattle. Proc. Br. Soc. Anim. Sci., Annual Meeting, p. 82. Browne, E.M., Bryant, M.J., Beever, D.E., Fisher, A.V., 2000. Intake, growth rate and carcass quality of beef cattle fed forage mixtures of grass silage and maize silage. Proc. Br. Soc. Anim. Sci., Annual Meeting, p. 72. Cammell, S.B., Sutton, J.D., Beever, D.E., Humphries, D.J., Phipps, R.H., 2000. The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows: 1. Energy and nitrogen utilization. Anim. Sci. 71, 381 – 390. Cuthbertson, A., Harrington, G., Smith, R.J., 1972. Tissue separation—to assess beef and lamb variation. In: Bichard, M. (Ed.), Proceedings of the British Society of Animal Production. Longman, Edinburgh, pp. 113 – 122. Easson, D.L., 2000. The effects of plastic mulch on the growth and development of forage maize in Northern Ireland. Seventy-third Annual Report of the Agricultural Research Institute of Northern Ireland, pp. 41 – 49. Keady, T.W.J., 1991. Studies on the mode of action of a bacterial inoculant as a silage additive and an evaluation of its efficacy. PhD thesis, The Queen’s University of Belfast. Keady, T.W.J., 2003. Maize silage in the diet of beef and dairy cattle—the influence of maturity at harvest and grass silage feed value, and feeding value relative to whole crop wheat. SeventySixth Annual Report of the Agricultural Research Institute of Northern Ireland, pp. 43 – 54. Keady, T.W.J., Kilpatrick, D.J., 2004. The effects of the inclusion of maize and whole crop wheat silages in grass silage-based diets on the performance of beef cattle offered two levels of concentrate. Proc. Br. Soc. Anim. Sci., Annual Meeting, p. 65. Keady, T.W.J., Mayne, C.S., Marsden, M., 1998. The effects of concentrate energy source on silage intake and animal performance with lactating dairy cows offered a range of grass silages. Anim. Sci. 66, 21 – 33. Keady, T.W.J., Mayne, C.S., McConaghy, D.A., Marsden, M., 1999. The effects of energy source and level of digestible undegradable protein in concentrates on silage intake and performance of lactating cows offered a range of grass silages. Anim. Sci. 68, 763 – 778. Keady, T.W.J., Mayne, C.S., Kilpatrick, D.J., 2002a. The effect of maturity of maize silage at harvest on the performance of lactating dairy cows offered two contrasting grass silages. Proc. Br. Soc. Anim. Sci., Annual Meeting, p. 16. Keady, T.W.J., Kilpatrick, C.M., Cushnahan, A., Murphy, J.A., 2002b. The cost of producing and feeding forages. Proceedings of the XIIIth International Silage Conference, Auchincruive, Scotland, pp. 322, 323. Keady, T.W.J., Mayne, C.S., Kilpatrick, D.J., 2003. The effect of maturity of maize silage at harvest on the performance of lactating dairy cows offered three contrasting grass silages. Proc. Br. Soc. Anim. Sci., Annual Meeting, p. 126. Kempster, A.J., Cook, G.L., Smith, R.J., 1980. The evaluation of a standardized commercial cutting technique for determining breed differences in carcass composition. J. Agric. Sci. 95, 431 – 440.
Kempster, A.J., Cuthbertson, A., Harrington, G., 1982. Beef carcass grading and classification. Carcase Evaluation in Livestock Breeding, Production and Marketing. Granada, London, pp. 163 – 201. Lawes Agricultural Trust, 1998. Genstat 5 for Windows, Version 4.1. Clarendon Press, Oxford. McCabe, N.H., O’Mara, F.P., Caffery, P.J., 1995. Evaluation of maize silage in the diet of finishing steers. Proc. Br. Soc. Anim. Sci., Annual Meeting, pp. 161 – 162. O’Kiely, P., Moloney, A., 1995. Performance of beef cattle offered different ratios of grass and maize silage. Ir. J. Agric. Food Res. 34, 76. O’Kiely, P., Moloney, A., 2000. Nutritive value of maize and grass silage for beef cattle when offered alone or in mixtures. Summary of Papers Presented at the Agricultural Research Forum, Faculty of Agriculture, University College Dublin, Belfield, Dublin, pp. 99 – 100. O’Mara, F.P., Fitzgerald, J.J., Murphy, J.J., Rath, M., 1998. The effect on milk production of replacing grass silage with maize silage in the diet of dairy cows. Livest. Prod. Sci. 55, 79 – 87. Phipps, R.H., Weller, R.F., Rook, A.J., 1992. Forage mixtures for dairy cows: the effect on dry matter intake and milk production of incorporating different proportions of maize silage into diets based on grass silages of differing energy value. J. Agric. Sci. 118, 379 – 382. Phipps, R.H., Sutton, J.D., Jones, B.A., 1995. Forage mixtures for dairy cows: the effect on dry matter intake and milk production of incorporating either fermented or urea-treated whole-crop wheat, brewers’ grains fodder beet or maize silage into diets based on grass silage. Anim. Sci. 61, 491 – 496. Phipps, R.H., Sutton, J.D., Beever, D.E., Jones, A.K., 2000. The effect of crop maturity on the nutritional value of maize silage for lactating dairy cows: 3. Food intake and milk production. Anim. Sci. 71, 401 – 409. Steen, R.W.J., 1984. A comparison of two-cut and three-cut systems of silage making for beef cattle using two cultivars of perennial ryegrass. Anim. Prod. 38, 171 – 179. Steen, R.W.J., 1992. The performance of beef cattle given silages made from perennial ryegrasses of different maturity groups, cut on different dates. Gr. For. Sci. 47, 239 – 248. Steen, R.W.J., 1996. Effects of protein supplementation of grass silage on the performance and carcass quality of beef cattle. J. Agric. Sci. 127, 403 – 412. Steen, R.W.J., Kilpatrick, D., 1995. Effects of plane of nutrition and slaughter weight on the carcass composition of serially slaughtered bulls, steers and heifers of three breed crosses. Livest. Prod. Sci. 43, 205 – 213. Steen, R.W.J., Gordon, F.J., Dawson, L.E.R., Park, R.S., Mayne, C.S., Agnew, R.E., Kilpatrick, D.J., Porter, M.G., 1998. Factors affecting the intake of grass silage by cattle and the prediction of silage intake. Anim. Sci. 66, 115 – 127. Thomas, C., Gibbs, B.G., Beever, D.E., Thurnham, B.R., 1988. The effect of date of cut and barley substitution on gain and on the efficiency of utilisation of grass silage by growing cattle: 1. Gains in live weight and its components. Br. J. Nutr. 60, 297 – 306. Weller, R.F., Phipps, R.H., 1986. The effect of silage preference on the performance of dairy cows. Anim. Prod. 42, 435 (Abstract).
The effect of quality of grass and maize silage on the intake and performance of beef cattle R.M. Kirkland *, D.C. Patterson 1 The Agricultural Research Institute of Northern Ireland, Hillsborough, Co. Down, Northern Ireland BT26 6DR, UK Received 11 April 2005; received in revised form 9 August 2005; accepted 24 August 2005
Abstract A study was undertaken to evaluate the effects of incorporating high (HMS) and low (LMS) maturity maize silages into diets based on low (LGS) and high (HGS) feed value grass silages offered to beef cattle. Seventy-two continental cross-bred steers were used in a 14-week continuous design, randomised block experiment. The six treatments were arranged as a 2 3 factorial design incorporating the LGS and HGS offered as the sole forage, along with each of the two grass silages offered in a 60:40 ratio (DM basis) with the HMS and LMS. All diets were supplemented with 3 kg/head/day concentrates. Total daily DM and metabolisable energy intakes were higher ( P b 0.001) for diets based on HGS compared to those based on LGS. Intakes were similar ( P N 0.05) between diets containing LMS and HMS, both of which were higher ( P b 0.001) than diets containing grass silage as the sole forage. Highest DM intakes were recorded with a mixture of HGS and HMS ( P b 0.05 or greater). Cattle offered diets containing HGS had higher live-weight gain ( P b 0.05), final live weight, carcass gain and carcass weight ( P b 0.001) than those offered diets containing LGS. Feed conversion efficiency, assessed on a carcass gain basis, was poorer ( P b 0.05) with diets containing LGS compared with those containing HGS, though differences between diets containing either LMS or HMS and GS as the sole forage were not significant ( P N 0.05). D 2005 Elsevier B.V. All rights reserved. Keywords: Grass silage; Maize silage; Intake; Beef cattle; Animal performance
1. Introduction The development of early maturing maize varieties, and the introduction of the complete cover * Corresponding author. Tel.: +44 28 9268 2484; fax: +44 28 9268 9594. E-mail address: [email protected] (R.M. Kirkland). 1 Also a member of The Queen’s University of Belfast, Belfast, Northern Ireland BT9 5PX, and the Department of Agriculture and Rural Development for Northern Ireland. 0301-6226/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.08.015
plastic mulch system of maize production, has considerably improved the potential and viability of maize as an alternative forage for use in ruminant production systems in areas of the UK and Western Europe which are climatically marginal for growing maize (Keady, 2003). Furthermore, recent estimates indicate that production costs of maize silage (MS) can be competitive with those of grazed grass and grass silage (GS) (Keady et al., 2002b).
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A number of studies have reported positive effects on feed intakes when forage MS replaced GS either totally or as part of the forage base for beef cattle (McCabe et al., 1995; Browne et al., 2000; O’Kiely and Moloney, 2000; Keady and Kilpatrick, 2004) and dairy cows (Keady et al., 2002a, 2003). However, improvements in forage intake, observed in many studies, have not consistently resulted in improved levels of animal performance (O’Kiely and Moloney, 2000) such that the production, and ultimately financial, implications of incorporating MS into the diet of beef cattle is not clear. Furthermore, few studies have examined the effects of offering diets incorporating GS and MS of differing qualities on the performance of beef cattle. Given the suitability of the climate in many areas of Western Europe for the production of high yielding crops of GS, it is likely that GS will remain the predominant forage in areas more marginal for maize production. However, given the variability in the quality of forage produced (Steen et al., 1998; Easson, 2000), it is important to evaluate the effects on animal production of incorporating MS differing in nutritive value into GS-based diets. The objective of the present study was to examine the effects on forage intake, animal performance and carcass characteristics of including MS, harvested at different stages of maturity, as a component of GSbased diets, in comparison to GS of differing feed value offered as the sole forage.
2. Materials and methods 2.1. Preparation of silages All silages were prepared from material harvested throughout the 2001 season. Two grass silages differing in feed value were harvested using precision chop forage harvesters and ensiled in clamp silos. The high feed value GS (HGS) was ensiled from primary growth herbage of a perennial ryegrass dominant sward between the 18 and 22 May, following a 36-h wilt, and treated with an additive (Ecosyl; Ecosyl Products Ltd., Middlesborough, UK). The low feed value GS (LGS) was ensiled from the second regrowth of a perennial ryegrass dominant sward on
the 20–21 September (without additive) following a 30-h wilt. High-maturity maize silage (HMS) was harvested in late October from the early variety Passat, while low-maturity MS (LMS) was harvested in early November from the later maturing variety Loft. Both MS were precision chopped, treated with additive (Ecocorn; Ecosyl Products Ltd., Middlesborough, UK) and ensiled in clamp silos. 2.2. Animals and experimental design Seventy-two continental cross-bred steers (mean initial live weight 485 kg; S.D. 24.0) were used in a 14-week continuous design, randomised block experiment. Animals were blocked into groups of six animals according to similarity of live weight, and one animal from each block allocated at random to one of six dietary treatments, giving 12 observations per treatment. The treatments were arranged as a 2 3 factorial design incorporating 2 GS (HGS and LGS) and 3 MS (HMS, LMS and no MS). The six dietary treatments comprised the 2 GS offered as the sole forage, along with each of the two GS offered in a 60:40 ratio (GS/MS on a dry matter [DM] basis) with both HMS and LMS. The silage mixtures were blended and offered once daily through individual Calan Broadbent gates. The quantity of each forage in the mix was determined daily based on the mean DM concentration of the forages over the previous 3 days. All forages were offered ad libitum to enable a 50 to 100 g/kg refusal. The quantities of forage offered to, and refused by, each individual animal were recorded daily, and uneaten material discarded on a daily basis. All diets were supplemented with 3 kg/head/day concentrates which were presented in the food box once daily on top of the forage mixture. Concentrate was formulated such that the crude protein (CP) concentration of the diet with the lowest determined CP concentration was 140 g/kg DM. The concentrate consisted of the following ingredients (g/ kg fresh weight): barley (425), soya bean meal (250), molassed sugarbeet pulp (150), maize meal (150) and mineral supplement (25). 2.3. Measurements Animals were weighed on 2 consecutive days at the beginning of each of the first 3 weeks of the study,
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at weekly intervals thereafter, and on 2 consecutive days prior to slaughter. Live weight gain of each animal was calculated by linear regression of live weight against time (days). Estimated rate of carcass gain was calculated by assuming an initial carcass weight for all animals of 0.52 of initial live weight, which was determined from similar animals in previous studies at this Institute (Keady, 1991). Following slaughter, all carcasses were graded visually for conformation and fatness using the five point scale of the European Carcass Classification Scheme (Kempster et al., 1982). The depth of subcutaneous fat over the eye muscle (m. longissimus dorsi) was measured at points a quarter, half and three-quarters way across the width of the eye-muscle at the 10th rib on both sides of each carcass. The amount of marbling fat in the cut surface of the eye-muscle was assessed independently by two individuals using the eight-point scale of the United States Department of Agriculture photographic standards (Agricultural Research Council, 1965). A photograph was taken of the cut surface of the eye-muscle at the 10th rib on both sides of each carcass and the area of each determined using a DeltaT Devices leaf-area machine. Weights of kidney, cod and channel fat, removed during the dressing procedure of each carcass, were recorded from each animal. After chilling, the fore-rib joint was removed from the left side of each carcass as described by Kempster et al. (1980) and was fully dissected into separable lean, separable fat and bone using the method described by Cuthbertson et al. (1972). 2.4. Digestibility studies and sample analyses Silage DM concentration was determined daily by drying at 85 8C, and the daily dried samples were bulked weekly for determination of acid detergent fibre (ADF), neutral detergent fibre (NDF) and ash. Further fresh silage samples were taken once weekly throughout the study and analysed for volatile corrected oven dry matter (VCODM) concentration, pH, nitrogen (N), NH3–N (proportion of total N), lactic acid, volatile fatty acids and alcohol concentrations and gross energy (GE). A representative sample of forage refusal for each treatment was analysed daily for oven DM concentration. Concentrates were sampled daily and bulked weekly for determination of DM, N, ash, ADF and NDF concentrations. Che-
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mical analyses were undertaken as described by Keady et al. (1998, 1999). The digestibilities of the six diets were determined through six cattle of similar live weight in a fourperiod, partially balanced, changeover design experiment, giving a total of four observations per diet, with all forages being offered ad libitum. Each period consisted of a 15-day feed-in period followed by a 6-day collection period of faeces and urine. The procedures for the determination of digestibility were similar to those described by Steen (1984), with feed and faecal samples being bulked for 3day periods and analysed for DM, organic matter (OM), N, ADF, NDF and GE concentrations. The DM concentration of each forage was determined daily while further silage samples were dried at 65 8C and bulked over 3-day periods for determination of water-soluble carbohydrate (WSC) and starch concentrations. The concentration of metabolisable energy (ME) of the total diets was determined by assuming that methane production was 0.07 of the GE intake. 2.5. Statistical analysis Data on the chemical composition of the forages offered were analysed by Analysis of Variance using Genstat 5 (Lawes Agricultural Trust, 1998). Data on food intake, animal performance and carcass characteristics were analysed using a two-way analysis of variance technique with forage type (GS or MS) as the main factor. For each individual factor analysed, live weight at the start of the study was incorporated into the analyses as a covariate. Data on total diet digestibility and concentration of ME were analysed using the REML technique in Genstat 5 with forage type (GS or MS) as the main factor.
3. Results 3.1. Grass silages The chemical compositions of the grass silages are presented in Table 1. Concentrations of DM, CP and lactic acid were lower ( P b 0.01 or greater), and concentrations of NH3–N (proportion of total N), propanol, acetic acid, ash, ADF and NDF higher ( P b 0.05
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Table 1 Chemical composition of the grass silagesa Grass silagesb LGS DM (g/kg) 251 pH 3.9 NH3–N (prop. total N) 0.10 Intake valued 74 Composition of DM (g/kg unless CP 131 Ethanol 11.8 Propanol 6.5 Acetic acid 27.9 Butyric acid 5.7 Propionic acid 1.4 Valeric acid 0.04 Lactic acid 82.8 Ash 97 ADF 313 NDF 538 WSC 8 GE (MJ/kg DM) 18.90
SED
Significancec
HGS 304 3.9 0.08 91 otherwise 152 11.6 0.8 17.2 2.5 0.9 0.09 112.5 83 300 502 41 18.77
8.0 0.06 0.004
*** NS ***
stated) 5.6 2.06 1.51 2.46 1.67 0.32 0.032 10.77 2.2 5.6 7.8 16.7 0.507
*** NS *** *** NS NS NS ** *** * *** NS NS
a DM, dry matter; CP, crude protein; ADF, acid detergent fibre; NDF, neutral detergent fibre; WSC, water-soluble carbohydrates; GE, gross energy. b LGS, low feed value grass silage; HGS, high feed value grass silage. c NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. d Predicted intake value from Hillsborough Feeding Information System (g DM/kg live weight0.75 ).
The chemical composition of the concentrate offered throughout the study was DM 838 g/kg, CP 198, ADF 84, NDF 187, ash 66 and predicted starch (using published values) 313 g/kg DM, and GE 17.9 MJ/kg DM. 3.3. Total diet digestibility and ME and CP concentrations Digestibility and CP and ME concentrations of the total diets are presented in Table 3. Diets based on HGS had higher ( P b 0.001) DM, OM, GE, ADF and NDF digestibilities, as well as N digestibility ( P b 0.05). Concentration of ME was also higher ( P b 0.05 or greater) for diets based on HGS (12.10 MJ/kg DM) compared to those based on LGS (11.66 MJ/kg DM). Digestibility of DM, OM, GE and N was similar ( P N 0.05) between diets containing LMS and HMS and those containing no MS (GS offered as the sole forage), whilst diets containing GS as the sole for-
Table 2 Chemical composition of the maize silagesa Maize silagesb LMS
or greater) in LGS compared to HGS. Silage type had no effect ( P N 0.05) on pH or concentrations of ethanol, butyric acid, propionic acid, valeric acid, WSC and GE. Silage intake potential (g DM/kg live weight0.75), predicted using the Hillsborough Feeding Information System (Steen et al., 1998), was 74 and 91 for the LGS and HGS, respectively. 3.2. Maize silages The chemical composition of the MS are presented in Table 2. Concentrations of DM and starch were lower ( P b 0.001), and concentrations of CP, ethanol, propanol, acetic acid, propionic acid, lactic acid, ADF, NDF and GE were higher ( P b 0.05 or greater) in LMS compared to HMS. Silage type had no effect ( P N 0.05) on pH, or concentrations of NH3–N (proportion of total N), butyric acid, valeric acid, ash and WSC.
SED
Significancec
HMS
DM (g/kg) 246 394 12.2 *** pH 3.9 4.0 0.04 NS NH3–N (prop. total N) 0.09 0.08 0.005 NS Composition of VCODM (g/kg unless otherwise stated) CP 80 75 0.2 *** Ethanol 9.4 4.3 1.36 *** Propanol 4.4 1.8 0.93 ** Acetic acid 32.8 12.9 2.13 *** Butyric acid 0.5 0.7 0.18 NS Propionic acid 1.3 0.5 0.36 * Valeric acid 0.0 0.0 0.00 NS Lactic acid 58.0 40.8 5.17 ** Ash 53 51 3.4 NS ADF 327 258 8.2 *** NDF 600 515 8.6 *** WSC 6.4 6.2 0.74 NS Starch 122 280 9.1 *** GE (MJ/kg DM) 18.88 18.31 0.203 ** a DM, dry matter; CP, crude protein; ADF, acid detergent fibre; NDF, neutral detergent fibre; WSC, water-soluble carbohydrates; GE, gross energy. b LMS, low-maturity maize silage; HMS, high-maturity maize silage. c NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001.
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Table 3 Digestibility and crude protein (CP) and metabolisable energy (ME) concentrations of the total diets Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
0.727 0.754 0.723 0.629 0.692 0.684 147.6 11.51
0.781 0.802 0.766 0.714 0.750 0.752 160.8 12.23
0.732 0.756 0.729 0.608 0.681 0.684 131.5 11.70
0.742 0.762 0.737 0.616 0.666 0.667 130.8 11.76
0.769 0.787 0.758 0.672 0.724 0.722 139.8 12.12
0.775 0.792 0.760 0.675 0.721 0.718 137.7 11.95
Digestibility coefficientsb DM OM GE N ADF NDF CP (g/kg DM) ME (MJ/kg DM)
SED
Grass
Maize
Grass Maize
0.0072 0.0072 0.0077 0.0395 0.0122 0.0119 4.93 0.267
*** *** *** * *** *** ** *
NS NS NS NS ** * *** NS
*** *** *** * *** *** *** *
NS, non-significant; *P b 0.05; **P b 0.01; *** P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage. b DM, dry matter; OM, organic matter; GE, gross energy; N, nitrogen; ADF, acid detergent fibre; NDF, neutral detergent fibre; ME, metabolisable energy.
age had higher ( P b 0.05) ADF and NDF digestibility (0.721 and 0.718, respectively) than those containing HMS (0.694 and 0.693, respectively). Dietary ME concentration was similar ( P N 0.05) between diets containing LMS, HMS and no MS. There were also significant interactions between diets based on each GS and MS in that digestibility of DM, OM and GE was lower ( P b 0.01 or greater) for diets containing LGS, or those containing LGS with either LMS or HMS, than those containing HGS (either as the sole forage or in combination with LMS or HMS). Digestibility of dietary N was higher ( P b 0.05) for diets containing HGS as the sole forage compared to diets containing forage mixtures of LGS and either LMS or HMS. Digestibility of ADF and NDF was higher ( P b 0.05 or greater) for diets containing HGS as the sole forage compared to all other diets (the only exception being the similar ( P N 0.05) ADF digestibility recorded between diets containing HGS as the sole forage and the HGS-LMS forage mixture). Forage mixtures containing HGS had higher ( P b 0.05 or greater) ADF and NDF digestibilities than diets containing LGS either as the sole forage or in combination with either LMS or HMS. Diets containing LGS as the sole forage had the lowest ME concentration, significantly ( P b 0.05) below diets containing HGS as the sole forage and diets containing the HGS-LMS forage mixture. Concentration of CP was highest ( P b 0.05 or greater) for diets containing HGS as the sole forage.
3.4. Food intake, animal performance and carcass data Data on food intake and animal performance are presented in Table 4. Total daily DM and ME intakes were greatest for diets based on HGS (9.39 kg/day and 113.6 MJ/day, respectively) compared to those based on LGS (8.38 kg/day and 97.7 MJ/day, respectively) ( P b 0.001). Dry matter and ME intakes were similar ( P N 0.05) between diets containing LMS (9.07 kg/ day and 108.1 MJ/day, respectively) and HMS (9.22 kg/day and 109.4 MJ/day, respectively), both of which were higher ( P b 0.001) than diets containing GS as the sole forage (8.37 kg/day and 99.5 MJ/day, respectively). Diets containing a mixture of HGS and HMS promoted higher ( P b 0.05 or greater) DM intakes than all other diets, whilst intakes of diets containing LGS as the sole forage were significantly lower ( P b 0.01 or greater) than all other diets. Cattle offered diets containing HGS had higher live-weight gain (1187 g/day) ( P b 0.05), final live weight (599 kg), estimated rate of carcass gain (857 g/day) and carcass weight (327 kg) ( P b 0.001) than those offered diets containing LGS (1050 g/day, 574 kg, 699 g/day and 310 kg, respectively). Feed conversion efficiency, assessed on a live-weight gain basis, was not influenced by type of forage offered in the diet ( P N 0.05). In contrast, feed conversion efficiency for carcass gain (DM basis) was poorer ( P b 0.05) with diets containing LGS (12.1 kg DM/ kg carcass gain) compared to those containing HGS
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Table 4 Effect of grass silage quality and inclusion of maize silage on food intake and animal performance Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
Total DM intake (kg/day) Total ME intake (MJ/day) Animal performance data Live-weight gain (g/day) Live weight at slaughter (kg) DMI/live-weight gain (kg/kg) Live-weight gain/MEI (g/MJ) Carcass gain (g/day) Carcass weight (kg) DMI/carcass gain (kg/kg) Carcass gain/MEI (g/MJ)
7.72 88.8
9.02 110.3
981 570 8.4 10.6 699 310 11.4 7.8
1166 596 7.8 10.5 808 325 11.0 7.6
8.90 104.1 1134 580 8.2 10.8 715 312 12.3 6.8
8.51 100.2 1037 573 8.5 10.2 683 308 12.5 6.7
9.25 112.1 1247 602 7.6 10.9 907 329 10.3 8.0
9.92 118.6 1147 600 8.1 10.4 858 327 12.0 7.1
SED
0.276 3.28 92.3 9.4 0.60 0.72 51.3 4.8 0.66 0.47
Grass
Maize
Grass Maize
*** ***
*** ***
*** ***
* *** NS NS *** *** * NS
NS NS NS NS NS NS NS NS
NS NS NS NS NS NS NS NS
NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage.
(11.1 kg DM/kg carcass gain), though differences between diets containing either LMS or HMS, and GS as the sole forage, fell just outside the accepted level of significance ( P = 0.054). Diet offered had no effect ( P N 0.05) on the efficiency of carcass gain per unit of MEI. Data on carcass characteristics are presented in Table 5. Forage type offered had no significant influence ( P N 0.05) on dressing proportion, carcass conformation or marbling score. In contrast, mean carcass fat class scores from animals offered diets containing
HGS (either as the sole forage or as a component of the total forage) were numerically, and in most instances significantly, higher than those offered diets containing LGS (up to P b 0.01) (treatment means of 3.3 and 2.8 for cattle offered diets containing HGS and LGS, respectively), while inclusion of MS did not influence this parameter ( P N 0.05). Similarly, subcutaneous fat depth and weight of internal fat depots were higher (at least P b 0.01) from carcasses of animals offered diets containing HGS (5.9 mm and 12.3 kg, respectively) compared to those offered LGS
Table 5 Effect of grass silage quality and inclusion of maize silage on carcass characteristics Forage offereda
Grass silage
LGS
HGS
LGS
LGS
HGS
HGS
Maize silage
–
–
LMS
HMS
LMS
HMS
546
546
532
534
544
539
Dressing proportion (g carcass per kg live weight) Carcass fat classb Carcass conformationc Depth of subcutaneous fat (mm) Marbling scored Internal fat depots (kg)e Area of longissimus dorsi (cm2) Composition of fore-rib joint (g/kg) Separable lean Separable fat Bone
2.5 2.8 3.5 2.4 8.4 70.8 633 160 192
3.4 2.6 6.5 2.8 12.5 66.8 580 245 175
2.9 2.5 3.9 2.8 11.1 66.8 632 188 180
3.1 2.5 5.0 2.6 11.0 64.9 626 184 183
3.2 2.7 5.2 2.5 12.1 70.4 639 187 167
3.2 2.6 6.1 2.4 12.2 72.8 598 216 177
Grass
Maize
Grass Maize
6.8
NS
NS
NS
0.23 0.14 0.70 0.22 0.83 3.07
** NS *** NS *** NS
NS NS NS NS NS NS
* NS NS NS * *
*** *** *
** * NS
** *** NS
SED
11.8 10.6 7.5
NS, non-significant; *P b 0.05; **P b 0.01; ***P b 0.001. a LGS, low feed value grass silage; HGS, high feed value grass silage; LMS, low-maturity maize silage; HMS, high-maturity maize silage. b 5-point scale: 1 = leanest; 5 = fattest. c 5-point scale: 1 = worst; 5 = best. d 8-point scale: 1 = low marbling; 8 = high marbling. e Sum of kidney, cod and channel fats.
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(4.1 mm and 10.2 kg, respectively). Area of m. longissimus dorsi was similar across GS and MS treatments (main effects) ( P N 0.05), but was lower ( P b 0.05) in carcasses from animals offered a forage mixture comprising LGS-HMS compared with those offered the HGS-HMS forage mixture. Analysis of data from dissection of the fore-rib joint showed that animals offered diets containing HGS had higher ( P b 0.001) separable fat and lower separable lean contents than those offered diets containing LGS. Similarly, mean separable fat contents were numerically, and in some instances significantly higher ( P b 0.05), and separable lean contents lower ( P b 0.01), in the fore-ribs of animals offered diets containing GS as the sole forage compared with those offered diets containing MS as a proportion of the forage component.
4. Discussion Data on the effects of maize silage inclusion in grass silage-based diets, assessed in terms of feed intake and animal performance, are necessary to provide a sound scientific basis on which to base nutritional feeding programmes for those involved in beef production. The objective of comparing silages of differing feeding value was achieved, with LGS having lower DM concentration, intake value and poorer fermentation characteristics than HGS. Similarly, LMS and HMS exhibited major differences when assessed in terms of DM, NDF and starch concentrations. 4.1. Digestibility of diets and ME and CP concentration Quality of GS was the main determinant of total diet digestibility recorded in the study, with diets containing HGS (either as the sole forage or in combination with MS) having higher digestibility coefficients (numerically and/or statistically) than other diets across all parameters assessed, primarily reflecting the early harvest date of the herbage from which HGS was produced. However, fibre digestibility tended to be lower with diets containing HMS compared to diets containing LMS, and was significantly lower compared to diets containing GS offered as the sole forage. Similarly, Cammell et al. (2000) reported
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a trend (non-significant) of reducing fibre digestibility when maize of increasing maturity (DM concentrations ranging from 226 up to 357 g/kg) was incorporated into a high-quality GS-based diet for dairy cows, albeit at a much higher rate (3:1 mixture of MS/GS on a DM basis), and incorporating higher rates of concentrate supplementation (8.7 kg DM/day), than that offered in the present study. Significant reductions in MS fibre digestibility with increasing maturity were also reported by Browne et al. (1999), when MS was offered as the sole forage to beef cattle (MS DM concentrations ranging from 273 to 314 to 367 g/kg) and in the study by Andrae et al. (2001). Nevertheless, differences in fibre digestibility recorded between diets containing LMS, HMS and no MS in the present study were not of sufficient magnitude to influence the overall digestibility of the DM component of the respective diets, all of which were similar. Whilst ME concentration of diets based on HGS (mean 12.10 MJ/kg DM) was significantly higher than those based on LGS (mean 11.66 MJ/kg DM), dietary ME concentration was similar between diets containing GS as the sole forage and those containing either of the two MS. This observation is in line with that of Cammell et al. (2000), who reported only marginal (non-significant) declines in dietary ME concentration across the range of MS maturities offered in their study, despite DM and starch concentrations of the most mature MS (357 g/kg and 401 g/kg DM, respectively) being greater than the higher maturity MS (HMS) in the present study. The present data indicate a marginally beneficial effect on dietary ME concentration of incorporating low-maturity MS into a diet based on poor-quality GS, although at the other extreme, ME concentrations tended to be reduced when MS was included in the diet, relative to diets containing HGS offered as the sole forage. While the diets offered in the present study were not formulated to be isonitrogenous, a key objective of the study was to ensure that intake and performance parameters of the cattle were not limited due to insufficient availability of N. Although total diet CP concentration ranged from 130.8 g/kg DM to 160.8 g/kg DM, it is unlikely that animal intake and performance characteristics were influenced by these differences, with Steen (1996) reporting no significant effects on food intake or performance characteristics of beef animals with diets in which the CP concentration
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ranged from approximately 130 g/kg DM to over 200 g/kg DM.
maize inclusion is not specifically a DM effect; therefore, the higher intake must be related to some other characteristic of ensiled forage maize.
4.2. Total diet DM and ME intake 4.3. Animal performance and carcass data Incorporating MS into the diets in the present study resulted in a significant ( P b 0.001) improvement in DM and ME intakes when compared to GS offered as the sole forage (means of 8.37 kg/day and 99.5 MJ/ day, 9.07 kg/day and 108.1 MJ/day, and 9.22 kg/day and 109.4 MJ/day for diets based on GS as the sole forage and those containing LMS and HMS, respectively). Improvements in intakes with inclusion of MS in GS-based diets have been demonstrated in previous studies with beef cattle (Browne et al., 2000; O’Kiely and Moloney, 2000) and with dairy cows (Phipps et al., 1995, 2000; O’Mara et al., 1998; Keady et al., 2002a, 2003). When analysed across individual treatments, the results from the present study demonstrate the potential to increase intakes of diets based on low-quality GS by substituting a proportion of the GS with MS of low or high maturity. The results also indicate the intake promoting effects of MS when included as part of a diet based on a high-quality GS. In the latter example, significant improvements in intakes were recorded when HMS was included in the diet, whilst the trend for higher intakes (relative to GS as the sole forage) with inclusion of LMS is in line with the higher intakes by beef cattle reported by O’Kiely and Moloney (1995) when a high-quality GS was partially replaced by MS of low maturity (205 g/kg DM, 0 g/kg DM starch). Although there is a paucity of studies in the literature which have compared both GS and MS of differing qualities in a single trial as was the case presently, Weller and Phipps (1986) and Phipps et al. (1992) reported improvements in DM intakes (with dairy cows) when MS was included as a component of a forage mixture based on GS of dlowT or dhighT quality. Furthermore, in line with the results of Phipps et al. (1992) from studies with dairy cows, the improvements in forage intakes with the mixed forage diets observed presently (relative to GS offered as the sole forage) were obtained without any significant effects on DM digestibility, indicating that this factor was not the major driving force promoting the higher intakes. There is also evidence from the present study that the improvement in intake with forage
Interactions between GS and MS treatments were absent for the majority of the animal performance traits measured in this study, though significant differences were recorded between main effects. Animals offered diets based on HGS had higher levels of performance across a number of the parameters assessed, while inclusion of MS in the diets generally had no significant influence on the level of performance obtained relative to that achieved where GS was offered as the sole forage. The significantly higher rates of live weight and carcass gains recorded with animals offered diets based on HGS compared with those of cattle offered diets based on LGS, generated 24.8 kg heavier live weight at slaughter and 16.7 kg heavier carcass weight. Despite these increases in animal weight parameters recorded, feed efficiency assessed on a liveweight gain basis was similar across all dietary treatments imposed. In contrast, differences in treatment means reached significance when assessed as kg DMI per kg carcass gain, feed efficiency being poorer (8.6% poorer) with animals offered diets based on LGS compared to those offered diets based on HGS. This difference derived from the 12.1% higher mean DMI achieved with the latter diet types compared with that of the former diet types, and the greater magnitude of the corresponding improvement in mean rate of carcass gain of 22.6%. However, inclusion of HMS in the diet, despite improving mean DMI by 10.2% relative to diets containing GS as the sole forage, resulted in only a marginal improvement in rate of carcass gain of 2.3%. These data concur with results from other studies reported in the literature, where improvements in food intake with inclusion of MS in GS-based diets have not resulted in concomitant improvements in rates of gain (O’Kiely and Moloney, 2000). Breen and Keane (2000) observed similar levels of beef animal performance when a mediumquality GS was partially replaced with a MS of very low maturity (192 g/kg DM, 27 g/kg DM starch), much lower than the maturity of either MS offered in the present study. These data indicate that inclusion
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of MS in the diet (even when of low quality) can give similar levels of animal performance relative to that of animals offered GS as the sole forage. Inclusion of MS in the diet had no significant influence on any of the main carcass parameters assessed in the study. These findings concur with results reported by other authors from studies in which MS was incorporated into a GS-based diet (McCabe et al., 1995; Breen and Keane, 2000). However, Browne et al. (2000) reported improved kill-out proportions, while O’Kiely and Moloney (2000) reported increased carcass fat class scores (numerically or significantly) of beef cattle offered diets containing MS compared to diets containing GS as the sole forage. Taken together, these data suggest that inclusion of MS in a GS-based diet, even when incorporated at rates up to 100% of the forage component of the diet, has no major or consistent effects on the main carcass characteristics. In a review of the influence of MS inclusion in the diet, Keady (2003) concluded that the doptimalT stage of maturity to harvest MS for dairy cows, based on fat plus protein yield, is approximately 300 g/kg DM. Given the DM concentration of the LMS (246 g/kg DM) and HMS (394 g/kg DM) in the present study, and the associated differences in other nutritional parameters, it is postulated that the absence of responses in animal performance to addition of MS to diets observed presently might reflect to some degree the disparity of these figures from the value quoted by Keady (2003) as doptimalT for dairy cow performance. In contrast to the data recorded with inclusion of MS in diets, quality of GS offered resulted in differences in carcass fat characteristics, with carcasses from animals offered diets containing HGS having higher fat class scores, subcutaneous fat depths, and greater mass of internal fat depots. It was initially postulated that these differences might reflect the higher growth rates and subsequent higher slaughter weights achieved by animals offered diets containing HGS compared to those offered diets containing LGS. Steen and Kilpatrick (1995) reported significant reductions in carcass fat characteristics when slaughter weights of bulls, steers and heifers were reduced by restricting intakes compared to animals offered feed ad libitum. However, re-analyses of the data in the present study after correction to constant carcass
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weight had no appreciable influence on carcass fat parameters, the covariate having no significant effect ( P N 0.05) on any of the measured variables. However, in contrast to the present data, Thomas et al. (1988) and Steen (1992) reported no effect on carcass fat characteristics when cattle were offered high compared to low digestibility GS, despite major differences in rates of carcass gain between the diets. If differences in carcass weight are not the major factor influencing the higher fat characteristics of animals offered diets containing HGS, it is probable that these differences at least partly reflect the higher ME intake and forage/concentrate ratio (and hence, increased acetate/propionate ratio) resulting from the improved forage intakes associated with animals offered diets containing HGS. Work by Beever et al. (1992) has suggested that a higher proportion of acetate in the rumen promotes greater synthesis of body fat.
5. Conclusions The results of the present study indicate that inclusion of MS in GS-based diets can improve DM intakes when offered to finishing beef cattle. However, the absence of improvements in feed efficiency and animal performance by incorporation of MS into the diet, relative to GS offered as the sole forage, probably reflects the extremes of maturity of the MS offered.
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