- Email: [email protected]
Herbage selection by cattle on sub-alpine wood pastures
Forest Ecology and Management 181 (2003) 39–50
Herbage selection by cattle on sub-alpine wood pastures Andrea C. Mayera,*, Veronika Sto¨cklia, Christine Huovinena, Werner Konoldb, Beda L. Estermannc, Michael Kreuzerc b
a WSL, Swiss Federal Institute for Snow and Avalanche Research, SLF, Flu¨elastrasse 11, CH-7260 Davos Dorf, Switzerland Institute of Landscape Management, Albert-Ludwigs-University of Freiburg, Tennenbacher Str. 4, D-79106 Freiburg, Germany c Institute of Animal Sciences, Animal Nutrition, Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum/LFW, CH-8092 Zurich, Switzerland
Received 1 November 2001; received in revised form 25 June 2002; accepted 14 September 2002
Abstract On botanically diverse sub-alpine wood pastures, the quantity and quality of the herbage available and consumed by cattle was investigated. Seven forest ranges located between 1560 and 2000 m a.s.l. in the Swiss Canton of Grisons were stocked with heifers, lactating and non-lactating cows. On average, the ranges consisted of 44% woodland, 25% half-open area (with young trees and shrubs) and 31% open area. The ranges were grazed applying a wide range of stocking rates (0.4–2.8 livestock units ha1) and grazing periods (12 to 114 days), with 6 to 65% of the herbage resources being exploited. Vegetation surveys were performed before and after grazing to determine the frequency of functional botanical groups in the herbage available and in that consumed. Herbage intake, selection and digestibility were determined using the double alkane technique applying controlled release capsules. On average, the daily herbage dry matter intake rates amounted to 1.3 and 1.8 kg 100 (kg live weight)1 in heifers and cows, respectively. Grass species were browsed on nearly half of the plots on which they occurred, whereas legumes, forbs and shrubs were browsed on approximately 20% of the plots. Although the herbage quantity provided by the pastures was quite small in some cases, cattle selected herbage of relatively constant digestibility throughout the approximately weekly pasture measurement periods (short-term response) and also after about 1 month of grazing of the same site (long-term response). The results show that the wood pastures, in conjunction with the ability of the animals to select sufficiently digestible plants, provide feed of a quality high enough to satisfy the requirements of livestock, at least in comparably extensive systems. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Agroforestry; Digestibility; Herbage selection; Range management; Stocking rate
1. Introduction In the Alps, there is a long tradition of multipurpose utilisation of agricultural and forest resources. Twelve percent of the Swiss mountain forests are grazed, mainly by cattle (Brassel and Bra¨ndli, 1999). To *
Corresponding author. Tel.: þ41-81-4170216; fax: þ41-81-4170110. E-mail address: [email protected] (A.C. Mayer).
underline other arguments against forest grazing, particularly damaging to young trees, it is claimed that sub-alpine wood pastures would only provide small amounts of herbage of low quality to cattle (Delucchi, 1993). Landau et al. (2000) emphasise that wood pastures may not totally cover the requirements of improved animal breeds. This implies that a separation of woodland and open pastures would raise only small economic disadvantages. However, the quality of the herbage available on mountain wood pastures has not
0378-1127/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(03)00127-0
40
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
yet been tested in studies with grazing cattle. Subalpine wood pastures consist of a mosaic of wooded, half-open and open areas and thus provide a high diversity in feed quality giving the opportunity to the animals to select palatable plants which have a higher digestibility than the average herbage available. Studies of Christen et al. (1996) and Berry et al. (2002) confirmed the selectivity of cattle grazing species-rich Alpine pastures. However, an increased grazing pressure may considerably reduce the opportunity to select appropriate plants (Walker et al., 1989). New experimental techniques allow the determination of herbage intake and digestibility on pasture (Berry et al., 2000; Estermann et al., 2001), but these methods have not yet been applied to wood pasture studies. The objectives of the present study were: (i) to describe and compare the quantity and quality of the herbage available on botanically diverse sub-
alpine wood pastures and the herbage consumed by various categories of cattle with different demands concerning feed quality; (ii) to compare the digestibility of the herbage consumed during the first and the second part of the weekly pasture measurement periods (short-term response); and (iii) to compare the quality of the herbage consumed during weekly periods at the beginning of the grazing period and after about 1 month of grazing the same site (long-term response).
2. Materials and methods 2.1. Experimental ranges and stocking regime The study comprised seven ranges traditionally stocked with cattle and located in the Dischma Valley
Table 1 Description of the experimental ranges Range
1
2
3
4
5
6
7
Size (ha)
6.5
1.0
19.3
3.0
3.4
9.3
5.4
Range composition Woodland (%) Half-open area (%)a Open area (%) Start of pasturing
50 0 50 May 26
60 0 40 June 8
42 14 44 June 20
14 68 18 July 4
14 68 18 August 3
54 23 23 July 13
28 50 22 August 25
1600 1700 65 S 41 110
1560 1580 40 N 78 110
1580 1700 50 N 114 110
1720 1800 60 S 10 100
1800 1850 60 S 12 100
1850 1950 60 S 64 90
1950 2000 60 S 32 90
1.0 0.4
1.2 0.9
0.5 0.5
2.8 0.3
1.6 0.2
0.5 0.3
0.4 0.1
Brown Swiss Dairy
Brown Swiss Dairy/heifer
Rha¨ tisches Grauvieh
Category
Brown Swiss Heifer
Non-lactating (dry) dairy/heifer
Total number
16
7
8/4
7/3
7/3
7/3
6
6
–
–
–
4/0; 6/0
Altitude (m a.s.l.) Min Max Slope, average (%) Aspect Actual grazing days Potential grazing daysb Stocking rate (livestock units ha1)c According to the actual grazing period According to the potential grazing periodb Cattle on range Breed
d
Number selected a
7/3
Characterised by the occurrence of shrubs and young trees. Given by Dietl et al. (1981) for (sub)alpine pastures; potential livestock density is lower when grazing over the complete grazing period is assumed. c LU; i.e. 600 kg body weight according to BLW/BUWAL (1994). d Animals which were subjected to the detailed individual measurements of herbage intake and digestibility. b
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
(468460 latitude N; 98530 longitude) near Davos, Swiss Canton of Grisons (Table 1). On average, the ranges consisted of 44% woodland, 31% open area and 25% half-open area (with shrubs and young trees). The Norway spruce (Picea abies) forest on Ranges 1 and 3 was relatively dense (approximately 350 trees ha1) becoming more open near the open pastures. The open pasture of Range 1 included some small groups of spruces (5–10 m height). The spruce stand on Range 2 was quite open (approximately 100 trees ha1). Ranges 4 and 5 had only small parts of forest and were dominated by a scattered spruce regeneration approximately 1–4 m high. Ranges 3 and 6 included shrub-dominated areas (mainly Vaccinium myrtillus) in the avalanche runs. Ranges 6 and 7 were close to the tree line; the forest contained approximately 200 spruces and larches (Larix decidua) per hectare. Table 1 gives the potential stocking rates, i.e. the actual rates extrapolated to the complete vegetative period for this altitude and inclination (potential grazing days) as specified by Dietl et al. (1981). The actual stocking rates often exceeded the potential stocking rate because pastures were mostly grazed only for part of the vegetative period. Overall, there was considerable variation in duration and stocking rate between the adherent pastures. 2.2. Vegetation survey On Ranges 2–7, before grazing commenced, we compiled lists of all plant species found within 20 cm 20 cm plots which were systematically selected on a grid of 50 m 50 m. Directly after the grazing period, the plant species on the plots were classified as ‘browsed’ and ‘not browsed’. Plant species were then subdivided into four functional botanical groups; grasses (Poaceae, Cyperaceae, Juncaceae), legumes, forbs and shrubs. These data were used to calculate the proportions of functional botanical groups in the herbage available and in the herbage consumed. 2.3. Herbage intake, excretion and digestibility Ranges 1, 2 and 6 were selected for additional, particularly intensive measurements. Within a total of four approximately weekly periods (two of them on Range 6), we measured dry matter and nutrient intake
41
from herbage as well as its digestibility in selected animals (Table 1). On Range 1, the detailed measurements were made over a period of 7 days (days 2–8 on this range). The six heifers selected on this range were either 1.5 or 2.5 years of age (1:1). On Range 2 measurements were carried out during the first 6 days. Performance of the cows on this range, as measured 2 months before the experiment started, was 20.0 (2.9) kg milk per day with 3.92 (0.33)% fat, 3.23 (0.23)% protein and 5.05 (0.08)% lactose. On Range 6, we performed two measurement periods, one of 7 days at the beginning of the vegetative period (days 1–7 on pasture, four cows investigated) and one of 5 days in the middle of the vegetative period (days 26–31 on pasture, six cows investigated, among them the four cows that were employed before). For further calculations, it was assumed that the herbage intake per LU (livestock unit) on Ranges 4, 5 and 7 was the same as that on Range 6 and the herbage intake per LU on Range 3 was the same as that on Range 2, since the same animal categories were grazing the ranges. It was also assumed that the herbage intake measured during the experimental weeks was representative for the whole grazing period. This allowed the calculation of the rates of exploitation of herbage with the differences of the herbage available, as estimated from the biomass samples taken, and the herbage consumed. However, it has to be considered that this approach does not account for biomass growing during the measurement periods. We assessed the composition of the herbaceous and shrubby biomass (dead and alive) before the start of the grazing period by cutting samples approximately 2 cm above ground on 20 cm 20 cm squares next to the plots, where the vegetation survey were performed. After clipping, the material was frozen. Intake as well as faecal excretion and digestibility of herbage and nutrients were assessed by applying the double indicator technique. This method is based on odd chain alkanes prevalent in herbage (internal markers) and dosed even chain alkanes (external markers; Mayes et al., 1986). Controlled Release Capsules (CRC’s; Captec Ltd., Auckland, New Zealand), as described and tested by Berry et al. (2000), and especially for herbage-only rations, by Estermann et al. (2001), were orally introduced into the rumen of the cattle 6 days prior to the collection period. The CRC’s release known daily amounts of indigestible C32 in the rumen. For the second measurement period
42
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
on Range 6 we did not use the CRC’s but administered C32 alkane mixed with 0.5 kg concentrate daily at 6 pm. One important pre-requisite of the double alkane indicator technique is to obtain herbage samples which ideally reflect the herbage consumed by the animals, since plant species and parts not only differ in nutrient but also in odd chain alkane concentrations. During the collection periods, we plucked herbage samples imitating the herbage intake pattern of the cattle 12 h a day switching between individual animals. Berry et al. (2002) successfully applied this method on botanically diverse alpine pastures. We collected spot faeces samples from fresh dung pats daily after rising of the animals in the morning, as recommended by Berry et al. (2000) and Estermann et al. (2001). Faeces collection lasted from 1 day after the start to 1 day after the end of the herbage collection to account for the delay from intake to excretion. The daily collected herbage and individual faeces samples were immediately frozen until analysis. Finally, we obtained samples of the concentrate fed additionally to the lactating cows (Range 2) and the non-lactating cows (medium stage of pasture season on Range 6). From all animals subjected to herbage intake measurement, urine spot samples were obtained. Daily in the morning after rising of the animals we captured 100 ml urine from the first urination in removable plastic bottles screwed into a funnel attached to a 1.5 m handle. The urine samples were frozen after collection, then defrosted after each collection week, cleaned from fibrous impurities by a plastic strainer and pooled equally for each cow. During the 6 days of measurement on Range 2 we also measured daily milk yield and collected samples from four milkings which were first frozen, then defrosted and pooled for each cow.
automatic weight loss measurement until weights remained constant. Fibre contents (crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF), and acid detergent lignin) of herbage and faeces samples were analysed according to standard procedures (Naumann and Bassler, 1997; Van Soest et al., 1991). We assessed nitrogen (N) contents of herbage, non-dried faeces, urine and milk using an automatic C/N analyser (type FP-2000, Leco Instruments, St. Joseph, MI, USA). Concentrations of urea in urine and in deproteinised (trichloroacetic acid, 0.3 ml l1) milk were determined enzymatically (method by Roche diagnostics, Basle, Switzerland). Urinary creatinine concentration was measured enzymatically with a commercial test kit (Unimate Crea 5, Roche) using an automatic colorimetric analyser (COBAS MIRA, Roche). The milk which had been collected in advance of the measurement period by the official milk control was conserved with Bronopol1 and analysed for fat, protein and lactose with infrared technique (Milkoscan 4000, Foss Electric, Hillerød, Denmark). The biomass samples were prepared and analysed in the same way as the samples of the herbage consumed, but only DM, OM, N and NDF were analysed. To calculate intake and digestibility of the herbage ingested as outlined by Berry et al. (2000), we determined the concentrations of n-alkanes (C29, C31, C32 and C33) in herbage, concentrate and faeces. For this purpose, we used a gas chromatograph (HP-6890, Hewlett-Packard, Waldbronn, Germany) equipped with a SPB-1 column (Supelco, Buchs, Switzerland) applying duplicate extraction and direct saponification. Herbage intake (kg DM per day) was calculated from the formula given by Mayes et al. (1986):
2.4. Laboratory analyses and calculations
where Fi, Ci and Hi are respective concentrations (mg kg1 DM) of either C29, C31 or C33 in faeces, concentrate (fed only in two of the experimental periods) and herbage. Fj, Cj and Hj are the respective concentrations (mg kg1 DM) of C32. Dj is the stated batch release rate for the CRC’s, Ic is the intake of concentrate (kg DM per day). The formula for cattle consuming only herbage is the same omitting Ci, Cj and Ic. In order to quantify herbage intake and faecal excretion, we used the average value obtained from the alkane ratios C29:C32, C31:C32 and C33:C32 to avoid
The individual herbage and faeces samples, combined for the first 3 days of the experimental period and for the respective residual days of the experimental periods, were dried at 60 8C for 48 h. After drying, we milled the samples through a 0.75 mm screen. By heating the samples in an automatic muffle furnace (TGA 500, Leco Instruments, St. Joseph, MI, USA) we analysed contents of dry matter (DM) and organic matter (OM) with steps at 105 and 550 8C using
herbage intake ¼
Fi =Fj ðDj þ Ic Cj Þ Ic Ci Hi Fi =ðFj Hj Þ
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
43
With Model 3, the effects of sub-period (days 1–3 ¼ Phase A versus days 4 to end of collection period ¼ Phase B; d), range (Ranges 1, 2 and 6; e) and the interaction between sub-period and range (n ¼ 6 per interaction sub-group mean value; de) were determined:
inherent uncertainties occurring with any of the ratios. Intake of nutrients was calculated from DM intake and nutrient concentrations, whereas coefficients of digestibility, which best describe the value of the herbage consumed, were derived from intake less faecal excretion as a percentage of intake. In cases when concentrate had been fed, values were corrected for known intake rates and digestibilities (tabulated values; RAP, 1999) in order to obtain the values concerning herbage. The daily excretion of urine N as an indicator of N excess in herbage was calculated by the formula given by Estermann et al. (2002): urine amount (kg per day) ¼ 9:553 þ 0:265 body weight ðkg0:75 Þ 1:174 creatinine ðmmol l1 Þ 3:138 urine N (g kg1). This estimation is based on the assumption that the daily creatinine excretion with urine is constant, whereas urinary N varies with herbage intake and composition (Estermann et al., 2002).
yijk ¼ m þ di þ ej þ ðdeÞij þ eijk For Model 3, only data of the medium stage of the pasture season on Range 6 were used. P-values <0.05 were considered significant.
3. Results 3.1. Vegetation survey and selection of functional botanical groups On Ranges 2 to 7, comprising 136 vegetation survey plots, overall 116 different plant species were found (26, 5, 72 and 13% grasses, legumes, forbs and shrubs, respectively; Table 2). Only 25 species occurred more frequently on more than 10% of the plots. In spite of the high proportion of forbs, only eleven forbs species occurred on more than 10% of the plots, whereas many other forbs species were found on a few plots only. Table 2 shows that the gross botanical composition of the standing herbage as reflected by the percentages of grasses, legumes, forbs and shrubs was similar over all ranges. Range 4 had the lowest percentage of grass species. Legume species were constantly low in number. The percentage of forbs was highest on Ranges 2 and 6. Shrub species, the proportion varying between 8 and 26%, were mainly represented by Vaccinium myrtillus and Vaccinium vitis-idaea. Over all ranges,
2.5. Statistical evaluation Statistical analyses were performed with Systat using the general linear model (GLM) procedure for analysis of variance (ANOVA; SPSS Inc., 1996). Model 1 tested the effects of age class of the heifers (1.5 versus 2.5 years, n ¼ 6; a) on Range 1: yij ¼ m þ ai þ eij Model 2 compared values of herbage intake and digestibility obtained in early and medium stage of pasture season (b; measured within cows (g), n ¼ 4) on Range 6: yijk ¼ m þ bðgÞi þ gj þ eijk
Table 2 Frequency of functional botanical groups and total number of species on Ranges 2–7 Functional groups
Number of species
Grass species Legume species Forb species Shrub species
26 5 72 13
Percentage of functional group (as availablea/as consumedb) All ranges
Range 2
Range 3
Range 4
Range 5
Range 6
Range 7
29/44 5/33 50/17 16/20
28/71 2/100 57/28 13/13
32/41 4/21 46/4 16/33
21/63 9/75 50/39 21/16
28/33 6/17 41/29 26/4
26/58 4/31 57/21 12/34
35/14 6/11 42/7 8/3
The first value gives the percentage of records of species of a certain botanical group in all plots investigated, the second value gives the percentage of recorded browsing relative to the number of total records of the respective functional botanical group. a As percentage of all plots. b As percentage of the number of records of the respective functional botanical group.
44
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
44% of the grass species and 33% of the legumes found on the plots were browsed during the grazing period, whereas only about 17% of the forbs and 20% of the shrubs were browsed (Table 2). This was different between ranges to a certain extent. On Range 3, the cattle browsed a relatively high percentage of the shrubs and a very low percentage of the forbs. 3.2. Nutrient composition of the herbage available and consumed Table 3 compares the composition of the herbage available and actually consumed on the first and last
day of the measurement periods, respectively, with the measurements comprising Ranges 1, 2 and 6 (two separate measurement periods, but only one assessment of composition of the herbage available). The herbage provided on Range 1 had the lowest content of OM and fibre (NDF) and a similarly low DM content as the herbage on Range 2. The N content was highest on Range 2, followed by Ranges 1 and 6. From the beginning, the 1.5-year-old heifers selected herbage with slightly higher contents of OM and fibre (NDF, ADF, acid detergent lignin and crude fibre) than the 2.5-year-old heifers. Both animal categories ingested herbage which was slightly lower
Table 3 Dry matter content and nutrient composition of herbage availablea and consumed on three selected ranges stocked with different livestock categories Range (animal category) Stage of pasture season Number of animals Experimental period (days)
1 (1.5-Year-old heifers) Early 3 7
1 (2.5-Year-old heifers) Early 3 7
2 (Lactating cows) Early 6 6
6 (Dry cows) Early 4 7
6 (Dry cows) Medium 6 5
Dry matter (g kg1 wet weight) As availablea As consumed on the first dayb As consumed on the last dayb
200 172 226
200 186 233
201 214 245
236 241 292
341 321
Organic matter (g kg1 DM) As available As consumed on the first day As consumed on the last day
914 910 921
914 905 890
927 925 929
922 929 934
922 915
Nitrogen (g kg1 DM) As available As consumed on the first day As consumed on the last day
27 29 26
27 29 28
31 36 29
22 20 20
22 25
Neutral detergent fibre (g kg1 DM) As available As consumed on the first day As consumed on the last day
482 490 646
482 479 511
496 464 528
509 521 527
645 617
Acid detergent fibre (g kg1 DM) As consumed on the first day As consumed on the last day
264 327
276 285
251 286
283 322
345 342
Acid detergent lignin (g kg1 DM) As consumed on the first day As consumed on the last day
38 43
48 41
32 42
47 56
49 51
201 269
193 201
194 224
246 271
305 283
Crude fibre (g kg1 DM) As consumed on the first day As consumed on the last day a b
Composition of the biomass on pasture directly before the start of pasturing. Referring to the experimental period.
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
in OM content and higher in N content than the herbage available. All heifers consumed herbage with higher contents of NDF and ADF as well as crude fibre towards the end of the experimental period, but this was presumably also true for the herbage available which aged in the time between to some extent. The lactating cows grazing Range 2 initially selected herbage of higher N and lower fibre content compared to that of the standing sward. Contents of nitrogen decreased and contents of fibre and acid detergent lignin of the herbage selected increased considerably during the 6 days of the measurement period in early June. Compared to
45
the herbage available, the cows on Range 6 were found to consume herbage of higher fibre content from the beginning. The fibre content of the selected herbage reached very high levels in the second measurement period when the herbage was 1-month older and, therefore, represented a far more progressed vegetative stage. Shifts in the composition of the herbage selected during the 5–7 day measurement periods were relatively small. On Ranges 3, 4, 5 and 7 no separate intake measurements were made. The NDF contents of the herbage available on these ranges accounted for 515, 581, 581 and 578 g kg1 DM, respectively.
Table 4 Herbage and concentrate intake and herbage digestibility as consumed on three selected ranges stocked with different livestock categories (means S:D:) Range (animal category)
1 (2.5-Year-old heifers) Early 3 7
2 (Lactating cows) Early 6 6
6 (Dry cows)
6 (Dry cows)
Stage of pasture season Number of animals Experimental period (days)
1 (1.5-Year-old heifers) Early 3 7
Early 4 7
Medium 6 5
Live weight (kg)
405 87
608 16b
569 28
401 33
401 25
6.2 1.3 6.4 1.8 5.9 1.0 –
7.0 1.4 7.4 2.3 6.6 0.4 –
10.5 1.9 10.8 1.8 10.2 2.2 1.3 0.5
8.0 1.9 7.8 1.9 8.2 2.2 –
6.9 1.1 6.8 1.2 7.0 1.0 0.5
Organic matter Total Phase A Phase B
70.1 5.0 71.2 7.2 69.1 2.7
65.2 6.1 64.2 9.6 66.3 3.8
64.7 6.5 64.1 7.1 65.2 6.6
59.2 4.2 59.3 5.9 59.2 2.7
54.4 4.8c 53.7 5.7 56.0 4.3
Nitrogen Total Phase A Phase B
70.3 5.6 71.7 7.0 68.8 4.9
66.9 2.5 68.5 2.2 65.4 1.9
65.1 5.9 66.2 5.9 64.0 4.5
49.3 5.8 46.8 4.1 51.8 6.6
58.2 5.5c 55.4 6.1 61.3 4.0
Neutral detergent fibre Total Phase A Phase B
68.8 5.1 69.2 7.9 68.5 1.7
62.9 5.8 61.0 8.8 64.8 3.3
62.9 7.8 59.5 8.0 66.3 6.4
60.7 4.2 62.3 5.5 59.0 1.9
61.4 5.0 61.4 6.2 64.0 3.4
Urine variables Nitrogen (g kg1) Urea (g kg1) Nitrogen excretion (g day1)d
11.3 1.2 18.7 1.2 221 50
11.8 0.2 18.4 0.2 281 23
7.4 0.7 11.6 1.4 240 26
5.0 1.0 5.4 0.7 129 21
8.0 1.6 7.6 1.7 140 14
1
Herbage intake (kg DM day ) Total Phase Aa Phase Bb Extra concentrate (kg DM day1) Apparent herbage digestibility (%)
a
Phase A ¼ days 1–3 of the experimental period; Phase B ¼ residual days of the experimental period. Significantly (P < 0:05) different from 1.5-year-old heifers according to Model 1. c Significantly (P < 0:05) different from digestibility during early stage of pasture season according to Model 2. d Estimated according to the formula given by (Estermann et al., 2002). b
46
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
Table 5 Overall effect of range and grazing phase on various feed-related traits (means S:D:)a Grazing phaseb
A
B
Effect (P) Phase
Range
Phase range
Number of animals Herbage intake (kg DM 100 kg1 live weight)
18 1.7 0.3
18 1.6 0.3
0.579
0.002
0.752
Apparent digestibilities (%) Organic matter Nitrogen Neutral detergent fibre
61.9 8.9 63.8 8.3 61.5 7.6
62.3 7.6 63.8 4.8 65.4 4.7
0.861 0.947 0.094
0.000 0.000 0.177
0.958 0.141 0.551
a b
Data from Ranges 1, 2 and 6 (Range 6 only medium stage of pasture season) evaluated by Model 3. Phase A ¼ days 1–3 of the experimental period; Phase B ¼ residual days of the experimental period.
3.3. Intake and digestibility of the herbage
concentrate) in the medium stage of the season. There was not much difference in herbage intake between the two phases within the experimental periods when data over all animals on Ranges 1, 2 and 6 were evaluated by excluding the range effects with the statistical model (Table 5). The lack of difference is also obvious from the data obtained on the individual ranges (Table 4). The daily rate of DM intake 100 kg1 body weight was 1.5 and 1.2 kg in the 1.5- and 2.5-year-old heifers, respectively, whereas all cows ingested approximately 1.8 kg DM 100 kg1 body weight per day (Table 6). From the measured or estimated intake rates and stocking rates, a relatively high variation in exploitation rate of the herbage biomass available was calculated: it ranged from 6% (Range 7) to 65% (Range 2). The herbage selected by the heifers on Range 1 had the highest digestibility of all herbages on the ranges investigated (Table 4). The digestibility of OM ranged
The results of the intake and digestibility measurements performed with the alkane technique are shown in Table 4 and values found in the first and the last phases of the approximately weekly periods are given separately. Intake of DM per day of the 2.5-year-old heifers was higher by 13% than that of the 1.5-year-old heifers, and live weight was 50% higher. On average, the lactating cows grazing Range 2 consumed 11.8 kg DM per day, which comprised herbage and, additionally, 1.3 kg DM per day of concentrate. The average milk yield of the cows during the measurement period on Range 2 was 15.4 (2.6; mean S:D:) kg per day. Milk urea content was 170 (23) mg kg1 and milk N content was 5.3 (0.6) g kg1. The non-lactating cows on Range 6, which weighed 168 kg (30%) less than the dairy cows on Range 2, ingested 8 kg herbage DM per day in the early stage of the pasture season and 15% less herbage DM (but additional 0.5 kg per day of Table 6 Availability, intake and exploitation rate of the herbage available Range
1 a
1
2
740 1520 Herbage available (kg DM biomass ha ) Herbage intake (kg DM 100 (kg live weight)1 1.3 0.3 1.8 0.3 per day, means S.D.) Herbage intakee (kg DM ha1) 350 990 Exploitation of herbage available (%) 48 65 a
3
4
5
1200 1.8b
2410 1.8c
2410 1.8c
370 15
270 11
660 55
Herbage available estimated from the biomass samples collected before the start of the grazing period. Set equal to herbage intake on Range 2. c Set equal to herbage intake on Range 6 (average between early and medium). d Average of early (2:0 0:4) and medium (1:7 0:3) stage of pasturing sojour. e Estimated herbage intake per hectare during the whole grazing season. b
6
7
1280 2720 1.8d 0.3 1.8c 410 32
150 6
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
at 68%, that of N at 70% and that of NDF at 66%. The 2.5-year-old animals tended to select herbage of slightly lower digestibility than the younger heifers, but the difference between heifers of different age was not significant. The lactating cows digested 65% of the OM and N ingested, and NDF was digested to 63%. The OM digestibility found in the non-lactating cows on Range 6 was quite low in both measurement periods. However, the digestibility of NDF was nearly as high as that found in the cows on Range 2. Phase effects within the experimental period were not significant in any of the digestibility coefficients (Table 5). Effects of phase on NDF digestibility were contrary in individual groups; this was even noted comparing the early and the medium stage of vegetation on Range 6 (Table 4). Urinary N and urea concentrations as well as urine N excretion (as calculated with the use of creatinine concentrations) reflected higher excess of herbage N in the heifers than in the lactating and the dry cows (Table 4). The low value in the lactating cows, despite the highest N content of their herbage, resulted from the high protein (N) requirements for milk yield. Nevertheless, these cows were estimated to lose far more N through urine than the 82 15 g per day excreted with milk.
4. Discussion The main objective of the present investigation was to evaluate the assumption of Delucchi (1993) that sub-alpine wood pastures provide only low amounts of feed of poor quality to cattle. For that purpose herbage quality and intake were tracked on sub-alpine wood pastures differing in characteristics and stocking rate. 4.1. Experimental techniques New experimental approaches which offer the opportunity to determine herbage intake and digestibility on diverse pastures (Estermann et al., 2001; Berry et al., 2002) were applied in a wood pasture study for the first time. The accuracy of the double alkane technique used for that purpose depends on the success in collecting representative samples of the herbage actually ingested. This was ensured by imitating the intake behaviour of the cattle for most of the
47
daytime and detailed observation of their selection pattern. Although this approach is limited in its accuracy to a certain extent, the levels of herbage intake calculated confirmed the basic applicability of the approach. The heifers’ intake corresponded to levels found in heifers of another study on alpine pastures (Estermann, 2001) and also levels registered in lactating and non-lactating cows were as expected (Estermann et al., 2001) when accounting for the additional concentrate supply. Other variables may be prone to greater uncertainties such as the herbage available and, associated with that, its exploitation rate. It was difficult to obtain representative samples for biomass estimates from the pastures consisting of woodland, half-open and open pastures, particularly because this required decisions on which plants or plant parts were potential feed. Especially, the feed supply of Ranges 4, 5 and 7, with a high percentage of shrub species such as Vaccinium myrtillus, was probably overestimated, since cattle were found to utilise only the younger leaves of this shrub, but not the whole plant. 4.2. Herbage amount provided by wood pasture and its exploitation by cattle Amount and nutrient composition of the herbage on wood pastures are influenced by many factors, such as forest structure and length of the grazing period (Ferna´ ndez-Martos y Bermu´ dez-Can˜ ete, 1961; Sharrow, 1991). The amount of biomass per hectare available for grazing varied much, and some of the pastures provided considerable quantities of potential feed. Since the samples of the herbage available also contained woody branches of shrub species, and as a certain proportion of herbage is always lost by trampling, a level of 65% was more or less equivalent to a complete exploitation of all herbaceous material on Range 2, which was corroborated by the visual appearance of this pasture after grazing. The data suggest that biomass was more affected by the proportion of woodland than by altitude. The latter provides less herbaceous and shrubby biomass over the whole season with the consequence of less potential grazing days, but ranges had been utilised successively anyhow. The applied stocking rates (livestock units ha1) varied with the available biomass and the length of the grazing period. For sub-alpine wood
48
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
pastures, basically four stocking regimes are common which were also found on the investigated ranges: short grazing with high stocking rate either once (Ranges 4 and 5) or twice in spring and in autumn (Ranges 1 and 2), extended grazing over the whole grazing season with low stocking rate (Ranges 3 and 6) and short grazing with low stocking rate (Range 7). These different regimes resulted in potentially underutilised pastures (Ranges 4, 5 and 7), in one overgrazed pasture (Range 2, where on the last day a genuine lack of feed was observed in the cows) and pastures with intermediate exploitation rates, illustrating that wood pastures offer a great variety in options for utilisation. As the ranges included some densely wooded areas with low herbage supply, the product of stocking rate grazing days was lower than on alpine pastures located above the tree line (Berry et al., 2001a). 4.3. Herbage selection by the cattle The cattle were able to select herbage of relatively constant digestibility throughout the approximately weekly pasture measurement periods (short-term response) and also after about 1 month of grazing the same site (long-term response). This suggests that herbage selection is particularly intensive when the amount of herbage available becomes scarce (Range 2), or when the fibre content of the herbage available reaches unfavourably high levels (medium stage, Range 6). This is contrary to the findings of Walker et al. (1989) that selectivity decreases with decreasing forage. Christen et al. (1996) emphasised that unrestricted selection from a high diversity of herbage species enables the cattle to ingest the most digestible plants. This fact seems to be more important than a basically high average digestibility of the complete standing sward. The ranges investigated provided 116 different plant species, most of them forbs which occurred on few plots only. Berry et al. (2002) found 66 different forage plant species on an intensively utilised alpine pasture situated above the tree line, whereas an under-utilised alpine pasture was found to be far less diverse in plant species composition. As recorded on the plots, the cattle in the present study browsed a high percentage of the grass species compared to forbs. Also, Pordomingo and Rucci (2000) and Estermann et al. (2001) observed a preference of cows
for grass species. The comparatively low percentage of forbs consumed can only partly be explained by active selection. Cattle may have difficulties to find and ingest these plants, because many forbs found on the subalpine wood pastures are very small (e.g. Melampyrum sp.) compared to the grass species or have rosette-like basal leaves (e.g. Hieracium sp.). Legumes, which are supposed to have a high nutritional value (Landau et al., 2000), were also browsed quite frequently. Cattle browsed more than 20% of the shrubs found on the plots. Intensive browsing of shrubs is also reported from other studies (Kie and Boroski, 1996; Pordomingo and Rucci, 2000). In our experiment, especially Vaccinium myrtillus was heavily browsed. Also, Malkama¨ ki and Haeggstro¨ m (1997) emphasised that Vaccinium myrtillus was strongly or totally defoliated due to grazing. Taking into account the medium digestibility of the forage selected on the wood pastures, we can not support the assessment of Dietl (1990) that Vaccinium myrtillus has a nutritional value of 0. Gonza´ lez Herna´ ndez and Silva-Pando (1996) measured a digestibility of whole Vaccinium myrtillus plants of 27%. The nutritional values of many sub-alpine herbage plants are still unknown. There is further need to investigate sub-alpine herbage quality by analysing the plant parts which are actually consumed by the cattle. 4.4. Quality of the herbage selected in relation to the requirements of cattle A high herbage quality for feeding purposes is characterised by a high content of utilisable energy (corresponding to a low fibre content and a high OM and fibre digestibility) and a N content of at least 20 g kg1 DM, although excessive N levels are also undesirable (Berry et al., 2001a). Fibre which is also an important ingredient because it limits herbage intake by filling the gut (Mertens, 1987), was assessed by four different variables: NDF, ADF, crude fibre and acid detergent lignin. NDF, ADF and crude fibre describing slightly different fractions of fibre varied between groups in a similar way. Lignin, as the herbage constituent hindering fibre digestion most, also changed with fibre contents in the herbage analysed. Our results illustrate that the herbage consumed was at least of medium quality to cattle compared to typical herbage found on lowland pastures (RAP,
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
1999). Furthermore, urinary N and urea levels were sufficiently high confirming that protein supply by the herbage was adequate. The results of the fibre contents of the selected herbage indicate that herbage provided by Ranges 1 and 2, which are located at lower altitude, was superior to that on Range 6. Herbage quality decreased when reaching a medium vegetative stage. These findings are in accordance with those of Christen et al. (1996) and Berry et al. (2001b). Also the increase in lignin content with progressing vegetative stage was previously described for alpine herbage (Christen et al., 1996). Wood pastures were reported by Ro¨ sch (1992) to have even higher contents of crude protein and lower contents of crude fibre than open pastures at the beginning of the grazing period and, therefore, could be of a correspondingly higher feeding value at that time. Finally, the differences between ranges in chemical composition of herbage were clearly recovered in the apparent digestibilities of OM but, unexpectedly, not in fibre digestion. Therefore, the differences in herbage fibre content rather than in fibre digestibility were responsible for the different OM digestibilities. The feeding values of the herbage on Ranges 1 and 2 corresponded to values found on open alpine pastures which provided herbage with higher OM digestibility but similar NDF digestibility (Berry et al., 2001b). Overall the results disprove the assumption of Delucchi (1993) that wood pastures provide only low quality feed. The digestibility of the herbage selected was generally typical for nutritious plants (RAP, 1999). Despite the ability of cattle to select herbage of constant digestibility, the differences in nutrient contents between the herbage available and the herbage consumed remained small; this even when accounting for the over-estimation of the quality of the herbage available due to the assumed steady increase in fibre and lignin content within the measurement periods. Cattle with only moderate energy and nutrient requirements were obviously able to cover the complete or the major proportion of their energy and nutrient requirements for maintenance, growth and milk synthesis. The same was found for dairy goats browsing Mediterranean scrubland (Cabiddu et al., 1999; Landau et al., 2000). The experimental group with the highest demands for a high herbage quality were the lactating Brown Swiss cows. Although only very low amounts of additional concentrate were fed,
49
the decline in yield from 20 to 15 kg milk per day occurring within 2 months still reflected the typical slope of the lactation curve. In studies of Christen et al. (1996) on alpine pastures cows of a higher milk yield were found to be not sufficiently supplied with nutrients from herbage alone, which was at least partly explained by the rapid changes in altitude and climate in that environment (Berry et al., 2001b). In contrast, the cows in our study did not experience such changes when being transferred to Range 2. Extensive supplementary feeding in order to be able to graze high yielding cows is not advisable since this would mean an undesired nutrient import into the wood pastures, apart from the fact that the efficacy of concentrate on high altitude pastures is uncertain anyhow (Malossini et al., 1995; Berry et al., 2001a).
5. Conclusion Sub-alpine wood pastures, consisting of wooded, half-open and open areas, provide herbage of a sufficient quantity and quality to nourish cattle with moderate nutrient and energy requirements; this without the use of significant amounts of supplementary feeds. This provides the opportunity to establish extensive livestock systems on these pastures such as suckler beef cattle (calves staying with their dam until weaning), particularly when using slowly growing breeds, but also to maintain traditional systems based on heifers or dairy cows in their less productive stages of the reproduction cycle (end of lactation and dry period). It seems that these cattle categories are able to select feed of appropriate quality even under high grazing pressure (high short-term stocking rate and/ or extended grazing periods). This might, however, increase the risk of damages to young trees, an aspect which still has to be investigated.
Acknowledgements This study was part of the interdisciplinary project PRIMALP of ETH Zurich, Switzerland, and of the programme ‘Forest–Wildlife–Landscape’ of the Swiss Federal Research Institute WSL. We want to acknowledge here the valuable collaboration with the farmer families Hoffmann, Ehrensperger and Pertschy. We
50
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
are also grateful to the assistance of Bruno Jo¨ rg in technical issues and Carmen Kunz in the laboratory. References Berry, N.R., Scheeder, M.R.L., Sutter, F., Kro¨ ber, T.F., Kreuzer, M., 2000. The accuracy of intake estimation based on the use of alkane controlled-release capsules and faeces grab sampling in cows. Ann. Zootech. 49, 1–16. Berry, N.R., Jewell, P.L., Sutter, F., Edwards, P.J., Kreuzer, M., 2001a. Effect of concentrate on nitrogen turnover and excretion of P, K, Na, Ca and Mg in lactating cows rotationally grazed at high altitude. Livest. Prod. Sci. 71, 261–275. Berry, N.R., Sutter, F., Bruckmaier, R., Blum, J., Kreuzer, M., 2001b. Limitations of high-alpine grazing conditions for earlylactation cows: effects of energy and protein supplementation. Anim. Sci. 73, 149–162. Berry, N.R., Jewell, P.L., Sutter, F., Edwards, P.J., Kreuzer, M., 2002. Selection, intake, and excretion of nutrients by Scottish Highland suckler beef cows and calves, and Brown Swiss dairy cows in contrasting Alpine grazing systems. J. Agric. Sci. (Cambridge) 139, 437–453. BLW/BUWAL (Swiss Federal Office for Agriculture/for Environment, Forest and Landscape), 1994. Wegleitung fu¨ r den Gewa¨ sserschutz in der Landwirtschaft, LmZ, Berne, Switzerland, 100 pp. Brassel, P., Bra¨ ndli, U.-B. (Eds.), 1999. Schweizerisches Lansforstinventar. Ergebnisse der Zweitaufnahme 1993–1995, Birmensdorf, Eidgen. Forschungsanstalt fu¨ r Wald, Schnee und Landschaft. Bern, Bundesamt fu¨ r Umwelt, Wald und Landschaft. Bern, Stuttgart, Wien, Haupt. 442 pp. Cabiddu, A., Branca, A., Dcandia, M., Pes, A., Santucci, P.M., Masoero, B., Calamari, L., 1999. Relationship between body condition score, metabolic profile, milk yield and milk composition in goats browsing a Mediterranean shrubland. Livest. Prod. Sci. 61, 267–273. Christen, R.E., Kunz, P.L., Langhans, W., Leuenberger, H., Sutter, F., Kreuzer, M., 1996. Productivity, requirements and efficiency of feed and nitrogen utilisation of grass-fed early lactating cows exposed to high Alpine conditions. J. Anim. Physiol. Anim. Nutr. 76, 22–35. Delucchi, M., 1993. Waldweide aus forstlicher Sicht. Bu¨ ndner Wald, Jahrgang 46 (1), 12–15. Dietl, W., 1990. Alpweiden naturgema¨ ss nutzen. Landfreund No. 11, Arbeitsgemeinschaft zur Fo¨ rderung des Futterbaus, Swiss Federal Research Station of Agronomy and Agroecology, Zurich-Reckenholz, Switzerland, p. 3. Dietl, W., Berger, P., Ofner, M., 1981. Die Kartierung des Pflanzenstandortes und der futterbaulichen Nutzungseignung von Naturwiesen: Eidg. Forschungsanstalt fu¨ r landwirtschaftlichen Pflanzenbau und Arbeitsgemeinschaft zur Fo¨ rderung des Futterbaues, Zu¨ rich-Reckenholz, Switzerland. Estermann, B.L., 2001. Nutrient cycling in suckler beef systems including alpine grazing. Breed and calving season effects and comparison with other livestock system options. ETH Dis-
sertation Thesis No. 14228, Wissenschaftsverlag Vauk Kiel KG, Kiel, Germany, 118 pp. Estermann, B.L., Wettstein, H.-R., Sutter, F., Kreuzer, M., 2001. Nutrient and energy conversion of grass-fed dairy and suckler beef cattle kept indoors or on high altitude pasture. Anim. Res. 50, 477–493. Estermann, B.L., Sutter, F., Schlegel, P.O., Erdin, D., Wettstein, H.R., Kreuzer, M., 2002. Effect of calf age and dam breed on intake, energy expenditure and excretion of nitrogen, phosphorus and methane of beef cows with calves. J. Anim. Sci. 80, 1124–1134. Ferna´ ndez-Martos y Bermu´ dez-Can˜ ete, C., 1961. La ganaderı`a y la repoblacion forestal en la Sierra Morena cordobesa. Montes 17, 139–143. Gonza´ lez Herna´ ndez, M.P., Silva-Pando, F.J., 1996. Grazing effects of ungulates in a Galician oak forest (northwest Spain). For. Ecol. Manage. 88, 65–70. Kie, J.G., Boroski, B.B., 1996. Cattle distribution, habitats, and diets in the Sierra Nevada of California. J. Range Manage. 49 (6), 482–488. Landau, S., Perevolotsky, A., Bonfil, D., Barkai, D., Silanikove, N., 2000. Utilisation of low quality resources by small ruminants in Mediterranean agro-pastoral systems: the case of browse and aftermath cereal stubble. Livest. Prod. Sci. 64 (1), 39–49. Malkama¨ ki, E., Haeggstro¨ m, C.-A., 1997. Short term impact of Finnish landrace cattle on the vegetation and soil of a wood pasture in SW Finland. Acta Bot. Fen. 159, 1–25. Malossini, F., Bovolenta, S., Piras, C., Ventura, W., 1995. Effect of concentrate on herbage intake and milk yield of dairy cows grazing an alpine pasture. Livest. Prod. Sci. 43, 119–128. Mayes, R.W., Lamb, C.S., Colgrove, M.P., 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agric. Sci. (Cambridge), 107, 161–170. Mertens, D.R., 1987. Prediction intake and digestibility using mathematical models of ruminal function. J. Anim. Sci. 64, 1548–1558. Naumann, K., Bassler, R., 1997. Die chemische Untersuchung von Futtermitteln, Methodenbuch, vol. 3. VdLUFA-Verlag, Darmstadt, Germany. Pordomingo, A.J., Rucci, T., 2000. Red deer and cattle diet composition in La Pampa, Argentina. J. Range Manage. 53, 649–654. RAP, 1999. Fu¨ tterungsempfehlungen und Na¨ hrwerttabellen fu¨ r Wiederka¨ uer (Swiss Federal Research Station for Animal Production). Landwirtschaftliche Lehrmittelzentrale, Zollikofen, Switzerland. Ro¨ sch, K., 1992. Einfluss der Beweidung auf die Vegetation des Bergwaldes. Forschungsbericht 26, Nationalpark Berchtesgaden, Germany, 100 pp. Sharrow, S.H., 1991. Tree planting pattern effects on forage production in a Douglas-fir agroforest. Agrofor. Syst. 16, 167–175. SPSS Inc., 1996. SYSTAT 6.0 for Windows. Statistics. Chicago, USA. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fibre, neutral detergent fibre, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3597. Walker, J.W., Heitschmidt, R.K., Dowhower, S.L., 1989. Some effects of a rotational grazing treatment on cattle preference for plant communities. J. Range Manage. 42 (2), 143–148.
Herbage selection by cattle on sub-alpine wood pastures Andrea C. Mayera,*, Veronika Sto¨cklia, Christine Huovinena, Werner Konoldb, Beda L. Estermannc, Michael Kreuzerc b
a WSL, Swiss Federal Institute for Snow and Avalanche Research, SLF, Flu¨elastrasse 11, CH-7260 Davos Dorf, Switzerland Institute of Landscape Management, Albert-Ludwigs-University of Freiburg, Tennenbacher Str. 4, D-79106 Freiburg, Germany c Institute of Animal Sciences, Animal Nutrition, Swiss Federal Institute of Technology (ETH) Zurich, ETH Zentrum/LFW, CH-8092 Zurich, Switzerland
Received 1 November 2001; received in revised form 25 June 2002; accepted 14 September 2002
Abstract On botanically diverse sub-alpine wood pastures, the quantity and quality of the herbage available and consumed by cattle was investigated. Seven forest ranges located between 1560 and 2000 m a.s.l. in the Swiss Canton of Grisons were stocked with heifers, lactating and non-lactating cows. On average, the ranges consisted of 44% woodland, 25% half-open area (with young trees and shrubs) and 31% open area. The ranges were grazed applying a wide range of stocking rates (0.4–2.8 livestock units ha1) and grazing periods (12 to 114 days), with 6 to 65% of the herbage resources being exploited. Vegetation surveys were performed before and after grazing to determine the frequency of functional botanical groups in the herbage available and in that consumed. Herbage intake, selection and digestibility were determined using the double alkane technique applying controlled release capsules. On average, the daily herbage dry matter intake rates amounted to 1.3 and 1.8 kg 100 (kg live weight)1 in heifers and cows, respectively. Grass species were browsed on nearly half of the plots on which they occurred, whereas legumes, forbs and shrubs were browsed on approximately 20% of the plots. Although the herbage quantity provided by the pastures was quite small in some cases, cattle selected herbage of relatively constant digestibility throughout the approximately weekly pasture measurement periods (short-term response) and also after about 1 month of grazing of the same site (long-term response). The results show that the wood pastures, in conjunction with the ability of the animals to select sufficiently digestible plants, provide feed of a quality high enough to satisfy the requirements of livestock, at least in comparably extensive systems. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Agroforestry; Digestibility; Herbage selection; Range management; Stocking rate
1. Introduction In the Alps, there is a long tradition of multipurpose utilisation of agricultural and forest resources. Twelve percent of the Swiss mountain forests are grazed, mainly by cattle (Brassel and Bra¨ndli, 1999). To *
Corresponding author. Tel.: þ41-81-4170216; fax: þ41-81-4170110. E-mail address: [email protected] (A.C. Mayer).
underline other arguments against forest grazing, particularly damaging to young trees, it is claimed that sub-alpine wood pastures would only provide small amounts of herbage of low quality to cattle (Delucchi, 1993). Landau et al. (2000) emphasise that wood pastures may not totally cover the requirements of improved animal breeds. This implies that a separation of woodland and open pastures would raise only small economic disadvantages. However, the quality of the herbage available on mountain wood pastures has not
0378-1127/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(03)00127-0
40
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
yet been tested in studies with grazing cattle. Subalpine wood pastures consist of a mosaic of wooded, half-open and open areas and thus provide a high diversity in feed quality giving the opportunity to the animals to select palatable plants which have a higher digestibility than the average herbage available. Studies of Christen et al. (1996) and Berry et al. (2002) confirmed the selectivity of cattle grazing species-rich Alpine pastures. However, an increased grazing pressure may considerably reduce the opportunity to select appropriate plants (Walker et al., 1989). New experimental techniques allow the determination of herbage intake and digestibility on pasture (Berry et al., 2000; Estermann et al., 2001), but these methods have not yet been applied to wood pasture studies. The objectives of the present study were: (i) to describe and compare the quantity and quality of the herbage available on botanically diverse sub-
alpine wood pastures and the herbage consumed by various categories of cattle with different demands concerning feed quality; (ii) to compare the digestibility of the herbage consumed during the first and the second part of the weekly pasture measurement periods (short-term response); and (iii) to compare the quality of the herbage consumed during weekly periods at the beginning of the grazing period and after about 1 month of grazing the same site (long-term response).
2. Materials and methods 2.1. Experimental ranges and stocking regime The study comprised seven ranges traditionally stocked with cattle and located in the Dischma Valley
Table 1 Description of the experimental ranges Range
1
2
3
4
5
6
7
Size (ha)
6.5
1.0
19.3
3.0
3.4
9.3
5.4
Range composition Woodland (%) Half-open area (%)a Open area (%) Start of pasturing
50 0 50 May 26
60 0 40 June 8
42 14 44 June 20
14 68 18 July 4
14 68 18 August 3
54 23 23 July 13
28 50 22 August 25
1600 1700 65 S 41 110
1560 1580 40 N 78 110
1580 1700 50 N 114 110
1720 1800 60 S 10 100
1800 1850 60 S 12 100
1850 1950 60 S 64 90
1950 2000 60 S 32 90
1.0 0.4
1.2 0.9
0.5 0.5
2.8 0.3
1.6 0.2
0.5 0.3
0.4 0.1
Brown Swiss Dairy
Brown Swiss Dairy/heifer
Rha¨ tisches Grauvieh
Category
Brown Swiss Heifer
Non-lactating (dry) dairy/heifer
Total number
16
7
8/4
7/3
7/3
7/3
6
6
–
–
–
4/0; 6/0
Altitude (m a.s.l.) Min Max Slope, average (%) Aspect Actual grazing days Potential grazing daysb Stocking rate (livestock units ha1)c According to the actual grazing period According to the potential grazing periodb Cattle on range Breed
d
Number selected a
7/3
Characterised by the occurrence of shrubs and young trees. Given by Dietl et al. (1981) for (sub)alpine pastures; potential livestock density is lower when grazing over the complete grazing period is assumed. c LU; i.e. 600 kg body weight according to BLW/BUWAL (1994). d Animals which were subjected to the detailed individual measurements of herbage intake and digestibility. b
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
(468460 latitude N; 98530 longitude) near Davos, Swiss Canton of Grisons (Table 1). On average, the ranges consisted of 44% woodland, 31% open area and 25% half-open area (with shrubs and young trees). The Norway spruce (Picea abies) forest on Ranges 1 and 3 was relatively dense (approximately 350 trees ha1) becoming more open near the open pastures. The open pasture of Range 1 included some small groups of spruces (5–10 m height). The spruce stand on Range 2 was quite open (approximately 100 trees ha1). Ranges 4 and 5 had only small parts of forest and were dominated by a scattered spruce regeneration approximately 1–4 m high. Ranges 3 and 6 included shrub-dominated areas (mainly Vaccinium myrtillus) in the avalanche runs. Ranges 6 and 7 were close to the tree line; the forest contained approximately 200 spruces and larches (Larix decidua) per hectare. Table 1 gives the potential stocking rates, i.e. the actual rates extrapolated to the complete vegetative period for this altitude and inclination (potential grazing days) as specified by Dietl et al. (1981). The actual stocking rates often exceeded the potential stocking rate because pastures were mostly grazed only for part of the vegetative period. Overall, there was considerable variation in duration and stocking rate between the adherent pastures. 2.2. Vegetation survey On Ranges 2–7, before grazing commenced, we compiled lists of all plant species found within 20 cm 20 cm plots which were systematically selected on a grid of 50 m 50 m. Directly after the grazing period, the plant species on the plots were classified as ‘browsed’ and ‘not browsed’. Plant species were then subdivided into four functional botanical groups; grasses (Poaceae, Cyperaceae, Juncaceae), legumes, forbs and shrubs. These data were used to calculate the proportions of functional botanical groups in the herbage available and in the herbage consumed. 2.3. Herbage intake, excretion and digestibility Ranges 1, 2 and 6 were selected for additional, particularly intensive measurements. Within a total of four approximately weekly periods (two of them on Range 6), we measured dry matter and nutrient intake
41
from herbage as well as its digestibility in selected animals (Table 1). On Range 1, the detailed measurements were made over a period of 7 days (days 2–8 on this range). The six heifers selected on this range were either 1.5 or 2.5 years of age (1:1). On Range 2 measurements were carried out during the first 6 days. Performance of the cows on this range, as measured 2 months before the experiment started, was 20.0 (2.9) kg milk per day with 3.92 (0.33)% fat, 3.23 (0.23)% protein and 5.05 (0.08)% lactose. On Range 6, we performed two measurement periods, one of 7 days at the beginning of the vegetative period (days 1–7 on pasture, four cows investigated) and one of 5 days in the middle of the vegetative period (days 26–31 on pasture, six cows investigated, among them the four cows that were employed before). For further calculations, it was assumed that the herbage intake per LU (livestock unit) on Ranges 4, 5 and 7 was the same as that on Range 6 and the herbage intake per LU on Range 3 was the same as that on Range 2, since the same animal categories were grazing the ranges. It was also assumed that the herbage intake measured during the experimental weeks was representative for the whole grazing period. This allowed the calculation of the rates of exploitation of herbage with the differences of the herbage available, as estimated from the biomass samples taken, and the herbage consumed. However, it has to be considered that this approach does not account for biomass growing during the measurement periods. We assessed the composition of the herbaceous and shrubby biomass (dead and alive) before the start of the grazing period by cutting samples approximately 2 cm above ground on 20 cm 20 cm squares next to the plots, where the vegetation survey were performed. After clipping, the material was frozen. Intake as well as faecal excretion and digestibility of herbage and nutrients were assessed by applying the double indicator technique. This method is based on odd chain alkanes prevalent in herbage (internal markers) and dosed even chain alkanes (external markers; Mayes et al., 1986). Controlled Release Capsules (CRC’s; Captec Ltd., Auckland, New Zealand), as described and tested by Berry et al. (2000), and especially for herbage-only rations, by Estermann et al. (2001), were orally introduced into the rumen of the cattle 6 days prior to the collection period. The CRC’s release known daily amounts of indigestible C32 in the rumen. For the second measurement period
42
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
on Range 6 we did not use the CRC’s but administered C32 alkane mixed with 0.5 kg concentrate daily at 6 pm. One important pre-requisite of the double alkane indicator technique is to obtain herbage samples which ideally reflect the herbage consumed by the animals, since plant species and parts not only differ in nutrient but also in odd chain alkane concentrations. During the collection periods, we plucked herbage samples imitating the herbage intake pattern of the cattle 12 h a day switching between individual animals. Berry et al. (2002) successfully applied this method on botanically diverse alpine pastures. We collected spot faeces samples from fresh dung pats daily after rising of the animals in the morning, as recommended by Berry et al. (2000) and Estermann et al. (2001). Faeces collection lasted from 1 day after the start to 1 day after the end of the herbage collection to account for the delay from intake to excretion. The daily collected herbage and individual faeces samples were immediately frozen until analysis. Finally, we obtained samples of the concentrate fed additionally to the lactating cows (Range 2) and the non-lactating cows (medium stage of pasture season on Range 6). From all animals subjected to herbage intake measurement, urine spot samples were obtained. Daily in the morning after rising of the animals we captured 100 ml urine from the first urination in removable plastic bottles screwed into a funnel attached to a 1.5 m handle. The urine samples were frozen after collection, then defrosted after each collection week, cleaned from fibrous impurities by a plastic strainer and pooled equally for each cow. During the 6 days of measurement on Range 2 we also measured daily milk yield and collected samples from four milkings which were first frozen, then defrosted and pooled for each cow.
automatic weight loss measurement until weights remained constant. Fibre contents (crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF), and acid detergent lignin) of herbage and faeces samples were analysed according to standard procedures (Naumann and Bassler, 1997; Van Soest et al., 1991). We assessed nitrogen (N) contents of herbage, non-dried faeces, urine and milk using an automatic C/N analyser (type FP-2000, Leco Instruments, St. Joseph, MI, USA). Concentrations of urea in urine and in deproteinised (trichloroacetic acid, 0.3 ml l1) milk were determined enzymatically (method by Roche diagnostics, Basle, Switzerland). Urinary creatinine concentration was measured enzymatically with a commercial test kit (Unimate Crea 5, Roche) using an automatic colorimetric analyser (COBAS MIRA, Roche). The milk which had been collected in advance of the measurement period by the official milk control was conserved with Bronopol1 and analysed for fat, protein and lactose with infrared technique (Milkoscan 4000, Foss Electric, Hillerød, Denmark). The biomass samples were prepared and analysed in the same way as the samples of the herbage consumed, but only DM, OM, N and NDF were analysed. To calculate intake and digestibility of the herbage ingested as outlined by Berry et al. (2000), we determined the concentrations of n-alkanes (C29, C31, C32 and C33) in herbage, concentrate and faeces. For this purpose, we used a gas chromatograph (HP-6890, Hewlett-Packard, Waldbronn, Germany) equipped with a SPB-1 column (Supelco, Buchs, Switzerland) applying duplicate extraction and direct saponification. Herbage intake (kg DM per day) was calculated from the formula given by Mayes et al. (1986):
2.4. Laboratory analyses and calculations
where Fi, Ci and Hi are respective concentrations (mg kg1 DM) of either C29, C31 or C33 in faeces, concentrate (fed only in two of the experimental periods) and herbage. Fj, Cj and Hj are the respective concentrations (mg kg1 DM) of C32. Dj is the stated batch release rate for the CRC’s, Ic is the intake of concentrate (kg DM per day). The formula for cattle consuming only herbage is the same omitting Ci, Cj and Ic. In order to quantify herbage intake and faecal excretion, we used the average value obtained from the alkane ratios C29:C32, C31:C32 and C33:C32 to avoid
The individual herbage and faeces samples, combined for the first 3 days of the experimental period and for the respective residual days of the experimental periods, were dried at 60 8C for 48 h. After drying, we milled the samples through a 0.75 mm screen. By heating the samples in an automatic muffle furnace (TGA 500, Leco Instruments, St. Joseph, MI, USA) we analysed contents of dry matter (DM) and organic matter (OM) with steps at 105 and 550 8C using
herbage intake ¼
Fi =Fj ðDj þ Ic Cj Þ Ic Ci Hi Fi =ðFj Hj Þ
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
43
With Model 3, the effects of sub-period (days 1–3 ¼ Phase A versus days 4 to end of collection period ¼ Phase B; d), range (Ranges 1, 2 and 6; e) and the interaction between sub-period and range (n ¼ 6 per interaction sub-group mean value; de) were determined:
inherent uncertainties occurring with any of the ratios. Intake of nutrients was calculated from DM intake and nutrient concentrations, whereas coefficients of digestibility, which best describe the value of the herbage consumed, were derived from intake less faecal excretion as a percentage of intake. In cases when concentrate had been fed, values were corrected for known intake rates and digestibilities (tabulated values; RAP, 1999) in order to obtain the values concerning herbage. The daily excretion of urine N as an indicator of N excess in herbage was calculated by the formula given by Estermann et al. (2002): urine amount (kg per day) ¼ 9:553 þ 0:265 body weight ðkg0:75 Þ 1:174 creatinine ðmmol l1 Þ 3:138 urine N (g kg1). This estimation is based on the assumption that the daily creatinine excretion with urine is constant, whereas urinary N varies with herbage intake and composition (Estermann et al., 2002).
yijk ¼ m þ di þ ej þ ðdeÞij þ eijk For Model 3, only data of the medium stage of the pasture season on Range 6 were used. P-values <0.05 were considered significant.
3. Results 3.1. Vegetation survey and selection of functional botanical groups On Ranges 2 to 7, comprising 136 vegetation survey plots, overall 116 different plant species were found (26, 5, 72 and 13% grasses, legumes, forbs and shrubs, respectively; Table 2). Only 25 species occurred more frequently on more than 10% of the plots. In spite of the high proportion of forbs, only eleven forbs species occurred on more than 10% of the plots, whereas many other forbs species were found on a few plots only. Table 2 shows that the gross botanical composition of the standing herbage as reflected by the percentages of grasses, legumes, forbs and shrubs was similar over all ranges. Range 4 had the lowest percentage of grass species. Legume species were constantly low in number. The percentage of forbs was highest on Ranges 2 and 6. Shrub species, the proportion varying between 8 and 26%, were mainly represented by Vaccinium myrtillus and Vaccinium vitis-idaea. Over all ranges,
2.5. Statistical evaluation Statistical analyses were performed with Systat using the general linear model (GLM) procedure for analysis of variance (ANOVA; SPSS Inc., 1996). Model 1 tested the effects of age class of the heifers (1.5 versus 2.5 years, n ¼ 6; a) on Range 1: yij ¼ m þ ai þ eij Model 2 compared values of herbage intake and digestibility obtained in early and medium stage of pasture season (b; measured within cows (g), n ¼ 4) on Range 6: yijk ¼ m þ bðgÞi þ gj þ eijk
Table 2 Frequency of functional botanical groups and total number of species on Ranges 2–7 Functional groups
Number of species
Grass species Legume species Forb species Shrub species
26 5 72 13
Percentage of functional group (as availablea/as consumedb) All ranges
Range 2
Range 3
Range 4
Range 5
Range 6
Range 7
29/44 5/33 50/17 16/20
28/71 2/100 57/28 13/13
32/41 4/21 46/4 16/33
21/63 9/75 50/39 21/16
28/33 6/17 41/29 26/4
26/58 4/31 57/21 12/34
35/14 6/11 42/7 8/3
The first value gives the percentage of records of species of a certain botanical group in all plots investigated, the second value gives the percentage of recorded browsing relative to the number of total records of the respective functional botanical group. a As percentage of all plots. b As percentage of the number of records of the respective functional botanical group.
44
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
44% of the grass species and 33% of the legumes found on the plots were browsed during the grazing period, whereas only about 17% of the forbs and 20% of the shrubs were browsed (Table 2). This was different between ranges to a certain extent. On Range 3, the cattle browsed a relatively high percentage of the shrubs and a very low percentage of the forbs. 3.2. Nutrient composition of the herbage available and consumed Table 3 compares the composition of the herbage available and actually consumed on the first and last
day of the measurement periods, respectively, with the measurements comprising Ranges 1, 2 and 6 (two separate measurement periods, but only one assessment of composition of the herbage available). The herbage provided on Range 1 had the lowest content of OM and fibre (NDF) and a similarly low DM content as the herbage on Range 2. The N content was highest on Range 2, followed by Ranges 1 and 6. From the beginning, the 1.5-year-old heifers selected herbage with slightly higher contents of OM and fibre (NDF, ADF, acid detergent lignin and crude fibre) than the 2.5-year-old heifers. Both animal categories ingested herbage which was slightly lower
Table 3 Dry matter content and nutrient composition of herbage availablea and consumed on three selected ranges stocked with different livestock categories Range (animal category) Stage of pasture season Number of animals Experimental period (days)
1 (1.5-Year-old heifers) Early 3 7
1 (2.5-Year-old heifers) Early 3 7
2 (Lactating cows) Early 6 6
6 (Dry cows) Early 4 7
6 (Dry cows) Medium 6 5
Dry matter (g kg1 wet weight) As availablea As consumed on the first dayb As consumed on the last dayb
200 172 226
200 186 233
201 214 245
236 241 292
341 321
Organic matter (g kg1 DM) As available As consumed on the first day As consumed on the last day
914 910 921
914 905 890
927 925 929
922 929 934
922 915
Nitrogen (g kg1 DM) As available As consumed on the first day As consumed on the last day
27 29 26
27 29 28
31 36 29
22 20 20
22 25
Neutral detergent fibre (g kg1 DM) As available As consumed on the first day As consumed on the last day
482 490 646
482 479 511
496 464 528
509 521 527
645 617
Acid detergent fibre (g kg1 DM) As consumed on the first day As consumed on the last day
264 327
276 285
251 286
283 322
345 342
Acid detergent lignin (g kg1 DM) As consumed on the first day As consumed on the last day
38 43
48 41
32 42
47 56
49 51
201 269
193 201
194 224
246 271
305 283
Crude fibre (g kg1 DM) As consumed on the first day As consumed on the last day a b
Composition of the biomass on pasture directly before the start of pasturing. Referring to the experimental period.
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
in OM content and higher in N content than the herbage available. All heifers consumed herbage with higher contents of NDF and ADF as well as crude fibre towards the end of the experimental period, but this was presumably also true for the herbage available which aged in the time between to some extent. The lactating cows grazing Range 2 initially selected herbage of higher N and lower fibre content compared to that of the standing sward. Contents of nitrogen decreased and contents of fibre and acid detergent lignin of the herbage selected increased considerably during the 6 days of the measurement period in early June. Compared to
45
the herbage available, the cows on Range 6 were found to consume herbage of higher fibre content from the beginning. The fibre content of the selected herbage reached very high levels in the second measurement period when the herbage was 1-month older and, therefore, represented a far more progressed vegetative stage. Shifts in the composition of the herbage selected during the 5–7 day measurement periods were relatively small. On Ranges 3, 4, 5 and 7 no separate intake measurements were made. The NDF contents of the herbage available on these ranges accounted for 515, 581, 581 and 578 g kg1 DM, respectively.
Table 4 Herbage and concentrate intake and herbage digestibility as consumed on three selected ranges stocked with different livestock categories (means S:D:) Range (animal category)
1 (2.5-Year-old heifers) Early 3 7
2 (Lactating cows) Early 6 6
6 (Dry cows)
6 (Dry cows)
Stage of pasture season Number of animals Experimental period (days)
1 (1.5-Year-old heifers) Early 3 7
Early 4 7
Medium 6 5
Live weight (kg)
405 87
608 16b
569 28
401 33
401 25
6.2 1.3 6.4 1.8 5.9 1.0 –
7.0 1.4 7.4 2.3 6.6 0.4 –
10.5 1.9 10.8 1.8 10.2 2.2 1.3 0.5
8.0 1.9 7.8 1.9 8.2 2.2 –
6.9 1.1 6.8 1.2 7.0 1.0 0.5
Organic matter Total Phase A Phase B
70.1 5.0 71.2 7.2 69.1 2.7
65.2 6.1 64.2 9.6 66.3 3.8
64.7 6.5 64.1 7.1 65.2 6.6
59.2 4.2 59.3 5.9 59.2 2.7
54.4 4.8c 53.7 5.7 56.0 4.3
Nitrogen Total Phase A Phase B
70.3 5.6 71.7 7.0 68.8 4.9
66.9 2.5 68.5 2.2 65.4 1.9
65.1 5.9 66.2 5.9 64.0 4.5
49.3 5.8 46.8 4.1 51.8 6.6
58.2 5.5c 55.4 6.1 61.3 4.0
Neutral detergent fibre Total Phase A Phase B
68.8 5.1 69.2 7.9 68.5 1.7
62.9 5.8 61.0 8.8 64.8 3.3
62.9 7.8 59.5 8.0 66.3 6.4
60.7 4.2 62.3 5.5 59.0 1.9
61.4 5.0 61.4 6.2 64.0 3.4
Urine variables Nitrogen (g kg1) Urea (g kg1) Nitrogen excretion (g day1)d
11.3 1.2 18.7 1.2 221 50
11.8 0.2 18.4 0.2 281 23
7.4 0.7 11.6 1.4 240 26
5.0 1.0 5.4 0.7 129 21
8.0 1.6 7.6 1.7 140 14
1
Herbage intake (kg DM day ) Total Phase Aa Phase Bb Extra concentrate (kg DM day1) Apparent herbage digestibility (%)
a
Phase A ¼ days 1–3 of the experimental period; Phase B ¼ residual days of the experimental period. Significantly (P < 0:05) different from 1.5-year-old heifers according to Model 1. c Significantly (P < 0:05) different from digestibility during early stage of pasture season according to Model 2. d Estimated according to the formula given by (Estermann et al., 2002). b
46
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
Table 5 Overall effect of range and grazing phase on various feed-related traits (means S:D:)a Grazing phaseb
A
B
Effect (P) Phase
Range
Phase range
Number of animals Herbage intake (kg DM 100 kg1 live weight)
18 1.7 0.3
18 1.6 0.3
0.579
0.002
0.752
Apparent digestibilities (%) Organic matter Nitrogen Neutral detergent fibre
61.9 8.9 63.8 8.3 61.5 7.6
62.3 7.6 63.8 4.8 65.4 4.7
0.861 0.947 0.094
0.000 0.000 0.177
0.958 0.141 0.551
a b
Data from Ranges 1, 2 and 6 (Range 6 only medium stage of pasture season) evaluated by Model 3. Phase A ¼ days 1–3 of the experimental period; Phase B ¼ residual days of the experimental period.
3.3. Intake and digestibility of the herbage
concentrate) in the medium stage of the season. There was not much difference in herbage intake between the two phases within the experimental periods when data over all animals on Ranges 1, 2 and 6 were evaluated by excluding the range effects with the statistical model (Table 5). The lack of difference is also obvious from the data obtained on the individual ranges (Table 4). The daily rate of DM intake 100 kg1 body weight was 1.5 and 1.2 kg in the 1.5- and 2.5-year-old heifers, respectively, whereas all cows ingested approximately 1.8 kg DM 100 kg1 body weight per day (Table 6). From the measured or estimated intake rates and stocking rates, a relatively high variation in exploitation rate of the herbage biomass available was calculated: it ranged from 6% (Range 7) to 65% (Range 2). The herbage selected by the heifers on Range 1 had the highest digestibility of all herbages on the ranges investigated (Table 4). The digestibility of OM ranged
The results of the intake and digestibility measurements performed with the alkane technique are shown in Table 4 and values found in the first and the last phases of the approximately weekly periods are given separately. Intake of DM per day of the 2.5-year-old heifers was higher by 13% than that of the 1.5-year-old heifers, and live weight was 50% higher. On average, the lactating cows grazing Range 2 consumed 11.8 kg DM per day, which comprised herbage and, additionally, 1.3 kg DM per day of concentrate. The average milk yield of the cows during the measurement period on Range 2 was 15.4 (2.6; mean S:D:) kg per day. Milk urea content was 170 (23) mg kg1 and milk N content was 5.3 (0.6) g kg1. The non-lactating cows on Range 6, which weighed 168 kg (30%) less than the dairy cows on Range 2, ingested 8 kg herbage DM per day in the early stage of the pasture season and 15% less herbage DM (but additional 0.5 kg per day of Table 6 Availability, intake and exploitation rate of the herbage available Range
1 a
1
2
740 1520 Herbage available (kg DM biomass ha ) Herbage intake (kg DM 100 (kg live weight)1 1.3 0.3 1.8 0.3 per day, means S.D.) Herbage intakee (kg DM ha1) 350 990 Exploitation of herbage available (%) 48 65 a
3
4
5
1200 1.8b
2410 1.8c
2410 1.8c
370 15
270 11
660 55
Herbage available estimated from the biomass samples collected before the start of the grazing period. Set equal to herbage intake on Range 2. c Set equal to herbage intake on Range 6 (average between early and medium). d Average of early (2:0 0:4) and medium (1:7 0:3) stage of pasturing sojour. e Estimated herbage intake per hectare during the whole grazing season. b
6
7
1280 2720 1.8d 0.3 1.8c 410 32
150 6
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
at 68%, that of N at 70% and that of NDF at 66%. The 2.5-year-old animals tended to select herbage of slightly lower digestibility than the younger heifers, but the difference between heifers of different age was not significant. The lactating cows digested 65% of the OM and N ingested, and NDF was digested to 63%. The OM digestibility found in the non-lactating cows on Range 6 was quite low in both measurement periods. However, the digestibility of NDF was nearly as high as that found in the cows on Range 2. Phase effects within the experimental period were not significant in any of the digestibility coefficients (Table 5). Effects of phase on NDF digestibility were contrary in individual groups; this was even noted comparing the early and the medium stage of vegetation on Range 6 (Table 4). Urinary N and urea concentrations as well as urine N excretion (as calculated with the use of creatinine concentrations) reflected higher excess of herbage N in the heifers than in the lactating and the dry cows (Table 4). The low value in the lactating cows, despite the highest N content of their herbage, resulted from the high protein (N) requirements for milk yield. Nevertheless, these cows were estimated to lose far more N through urine than the 82 15 g per day excreted with milk.
4. Discussion The main objective of the present investigation was to evaluate the assumption of Delucchi (1993) that sub-alpine wood pastures provide only low amounts of feed of poor quality to cattle. For that purpose herbage quality and intake were tracked on sub-alpine wood pastures differing in characteristics and stocking rate. 4.1. Experimental techniques New experimental approaches which offer the opportunity to determine herbage intake and digestibility on diverse pastures (Estermann et al., 2001; Berry et al., 2002) were applied in a wood pasture study for the first time. The accuracy of the double alkane technique used for that purpose depends on the success in collecting representative samples of the herbage actually ingested. This was ensured by imitating the intake behaviour of the cattle for most of the
47
daytime and detailed observation of their selection pattern. Although this approach is limited in its accuracy to a certain extent, the levels of herbage intake calculated confirmed the basic applicability of the approach. The heifers’ intake corresponded to levels found in heifers of another study on alpine pastures (Estermann, 2001) and also levels registered in lactating and non-lactating cows were as expected (Estermann et al., 2001) when accounting for the additional concentrate supply. Other variables may be prone to greater uncertainties such as the herbage available and, associated with that, its exploitation rate. It was difficult to obtain representative samples for biomass estimates from the pastures consisting of woodland, half-open and open pastures, particularly because this required decisions on which plants or plant parts were potential feed. Especially, the feed supply of Ranges 4, 5 and 7, with a high percentage of shrub species such as Vaccinium myrtillus, was probably overestimated, since cattle were found to utilise only the younger leaves of this shrub, but not the whole plant. 4.2. Herbage amount provided by wood pasture and its exploitation by cattle Amount and nutrient composition of the herbage on wood pastures are influenced by many factors, such as forest structure and length of the grazing period (Ferna´ ndez-Martos y Bermu´ dez-Can˜ ete, 1961; Sharrow, 1991). The amount of biomass per hectare available for grazing varied much, and some of the pastures provided considerable quantities of potential feed. Since the samples of the herbage available also contained woody branches of shrub species, and as a certain proportion of herbage is always lost by trampling, a level of 65% was more or less equivalent to a complete exploitation of all herbaceous material on Range 2, which was corroborated by the visual appearance of this pasture after grazing. The data suggest that biomass was more affected by the proportion of woodland than by altitude. The latter provides less herbaceous and shrubby biomass over the whole season with the consequence of less potential grazing days, but ranges had been utilised successively anyhow. The applied stocking rates (livestock units ha1) varied with the available biomass and the length of the grazing period. For sub-alpine wood
48
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
pastures, basically four stocking regimes are common which were also found on the investigated ranges: short grazing with high stocking rate either once (Ranges 4 and 5) or twice in spring and in autumn (Ranges 1 and 2), extended grazing over the whole grazing season with low stocking rate (Ranges 3 and 6) and short grazing with low stocking rate (Range 7). These different regimes resulted in potentially underutilised pastures (Ranges 4, 5 and 7), in one overgrazed pasture (Range 2, where on the last day a genuine lack of feed was observed in the cows) and pastures with intermediate exploitation rates, illustrating that wood pastures offer a great variety in options for utilisation. As the ranges included some densely wooded areas with low herbage supply, the product of stocking rate grazing days was lower than on alpine pastures located above the tree line (Berry et al., 2001a). 4.3. Herbage selection by the cattle The cattle were able to select herbage of relatively constant digestibility throughout the approximately weekly pasture measurement periods (short-term response) and also after about 1 month of grazing the same site (long-term response). This suggests that herbage selection is particularly intensive when the amount of herbage available becomes scarce (Range 2), or when the fibre content of the herbage available reaches unfavourably high levels (medium stage, Range 6). This is contrary to the findings of Walker et al. (1989) that selectivity decreases with decreasing forage. Christen et al. (1996) emphasised that unrestricted selection from a high diversity of herbage species enables the cattle to ingest the most digestible plants. This fact seems to be more important than a basically high average digestibility of the complete standing sward. The ranges investigated provided 116 different plant species, most of them forbs which occurred on few plots only. Berry et al. (2002) found 66 different forage plant species on an intensively utilised alpine pasture situated above the tree line, whereas an under-utilised alpine pasture was found to be far less diverse in plant species composition. As recorded on the plots, the cattle in the present study browsed a high percentage of the grass species compared to forbs. Also, Pordomingo and Rucci (2000) and Estermann et al. (2001) observed a preference of cows
for grass species. The comparatively low percentage of forbs consumed can only partly be explained by active selection. Cattle may have difficulties to find and ingest these plants, because many forbs found on the subalpine wood pastures are very small (e.g. Melampyrum sp.) compared to the grass species or have rosette-like basal leaves (e.g. Hieracium sp.). Legumes, which are supposed to have a high nutritional value (Landau et al., 2000), were also browsed quite frequently. Cattle browsed more than 20% of the shrubs found on the plots. Intensive browsing of shrubs is also reported from other studies (Kie and Boroski, 1996; Pordomingo and Rucci, 2000). In our experiment, especially Vaccinium myrtillus was heavily browsed. Also, Malkama¨ ki and Haeggstro¨ m (1997) emphasised that Vaccinium myrtillus was strongly or totally defoliated due to grazing. Taking into account the medium digestibility of the forage selected on the wood pastures, we can not support the assessment of Dietl (1990) that Vaccinium myrtillus has a nutritional value of 0. Gonza´ lez Herna´ ndez and Silva-Pando (1996) measured a digestibility of whole Vaccinium myrtillus plants of 27%. The nutritional values of many sub-alpine herbage plants are still unknown. There is further need to investigate sub-alpine herbage quality by analysing the plant parts which are actually consumed by the cattle. 4.4. Quality of the herbage selected in relation to the requirements of cattle A high herbage quality for feeding purposes is characterised by a high content of utilisable energy (corresponding to a low fibre content and a high OM and fibre digestibility) and a N content of at least 20 g kg1 DM, although excessive N levels are also undesirable (Berry et al., 2001a). Fibre which is also an important ingredient because it limits herbage intake by filling the gut (Mertens, 1987), was assessed by four different variables: NDF, ADF, crude fibre and acid detergent lignin. NDF, ADF and crude fibre describing slightly different fractions of fibre varied between groups in a similar way. Lignin, as the herbage constituent hindering fibre digestion most, also changed with fibre contents in the herbage analysed. Our results illustrate that the herbage consumed was at least of medium quality to cattle compared to typical herbage found on lowland pastures (RAP,
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
1999). Furthermore, urinary N and urea levels were sufficiently high confirming that protein supply by the herbage was adequate. The results of the fibre contents of the selected herbage indicate that herbage provided by Ranges 1 and 2, which are located at lower altitude, was superior to that on Range 6. Herbage quality decreased when reaching a medium vegetative stage. These findings are in accordance with those of Christen et al. (1996) and Berry et al. (2001b). Also the increase in lignin content with progressing vegetative stage was previously described for alpine herbage (Christen et al., 1996). Wood pastures were reported by Ro¨ sch (1992) to have even higher contents of crude protein and lower contents of crude fibre than open pastures at the beginning of the grazing period and, therefore, could be of a correspondingly higher feeding value at that time. Finally, the differences between ranges in chemical composition of herbage were clearly recovered in the apparent digestibilities of OM but, unexpectedly, not in fibre digestion. Therefore, the differences in herbage fibre content rather than in fibre digestibility were responsible for the different OM digestibilities. The feeding values of the herbage on Ranges 1 and 2 corresponded to values found on open alpine pastures which provided herbage with higher OM digestibility but similar NDF digestibility (Berry et al., 2001b). Overall the results disprove the assumption of Delucchi (1993) that wood pastures provide only low quality feed. The digestibility of the herbage selected was generally typical for nutritious plants (RAP, 1999). Despite the ability of cattle to select herbage of constant digestibility, the differences in nutrient contents between the herbage available and the herbage consumed remained small; this even when accounting for the over-estimation of the quality of the herbage available due to the assumed steady increase in fibre and lignin content within the measurement periods. Cattle with only moderate energy and nutrient requirements were obviously able to cover the complete or the major proportion of their energy and nutrient requirements for maintenance, growth and milk synthesis. The same was found for dairy goats browsing Mediterranean scrubland (Cabiddu et al., 1999; Landau et al., 2000). The experimental group with the highest demands for a high herbage quality were the lactating Brown Swiss cows. Although only very low amounts of additional concentrate were fed,
49
the decline in yield from 20 to 15 kg milk per day occurring within 2 months still reflected the typical slope of the lactation curve. In studies of Christen et al. (1996) on alpine pastures cows of a higher milk yield were found to be not sufficiently supplied with nutrients from herbage alone, which was at least partly explained by the rapid changes in altitude and climate in that environment (Berry et al., 2001b). In contrast, the cows in our study did not experience such changes when being transferred to Range 2. Extensive supplementary feeding in order to be able to graze high yielding cows is not advisable since this would mean an undesired nutrient import into the wood pastures, apart from the fact that the efficacy of concentrate on high altitude pastures is uncertain anyhow (Malossini et al., 1995; Berry et al., 2001a).
5. Conclusion Sub-alpine wood pastures, consisting of wooded, half-open and open areas, provide herbage of a sufficient quantity and quality to nourish cattle with moderate nutrient and energy requirements; this without the use of significant amounts of supplementary feeds. This provides the opportunity to establish extensive livestock systems on these pastures such as suckler beef cattle (calves staying with their dam until weaning), particularly when using slowly growing breeds, but also to maintain traditional systems based on heifers or dairy cows in their less productive stages of the reproduction cycle (end of lactation and dry period). It seems that these cattle categories are able to select feed of appropriate quality even under high grazing pressure (high short-term stocking rate and/ or extended grazing periods). This might, however, increase the risk of damages to young trees, an aspect which still has to be investigated.
Acknowledgements This study was part of the interdisciplinary project PRIMALP of ETH Zurich, Switzerland, and of the programme ‘Forest–Wildlife–Landscape’ of the Swiss Federal Research Institute WSL. We want to acknowledge here the valuable collaboration with the farmer families Hoffmann, Ehrensperger and Pertschy. We
50
A.C. Mayer et al. / Forest Ecology and Management 181 (2003) 39–50
are also grateful to the assistance of Bruno Jo¨ rg in technical issues and Carmen Kunz in the laboratory. References Berry, N.R., Scheeder, M.R.L., Sutter, F., Kro¨ ber, T.F., Kreuzer, M., 2000. The accuracy of intake estimation based on the use of alkane controlled-release capsules and faeces grab sampling in cows. Ann. Zootech. 49, 1–16. Berry, N.R., Jewell, P.L., Sutter, F., Edwards, P.J., Kreuzer, M., 2001a. Effect of concentrate on nitrogen turnover and excretion of P, K, Na, Ca and Mg in lactating cows rotationally grazed at high altitude. Livest. Prod. Sci. 71, 261–275. Berry, N.R., Sutter, F., Bruckmaier, R., Blum, J., Kreuzer, M., 2001b. Limitations of high-alpine grazing conditions for earlylactation cows: effects of energy and protein supplementation. Anim. Sci. 73, 149–162. Berry, N.R., Jewell, P.L., Sutter, F., Edwards, P.J., Kreuzer, M., 2002. Selection, intake, and excretion of nutrients by Scottish Highland suckler beef cows and calves, and Brown Swiss dairy cows in contrasting Alpine grazing systems. J. Agric. Sci. (Cambridge) 139, 437–453. BLW/BUWAL (Swiss Federal Office for Agriculture/for Environment, Forest and Landscape), 1994. Wegleitung fu¨ r den Gewa¨ sserschutz in der Landwirtschaft, LmZ, Berne, Switzerland, 100 pp. Brassel, P., Bra¨ ndli, U.-B. (Eds.), 1999. Schweizerisches Lansforstinventar. Ergebnisse der Zweitaufnahme 1993–1995, Birmensdorf, Eidgen. Forschungsanstalt fu¨ r Wald, Schnee und Landschaft. Bern, Bundesamt fu¨ r Umwelt, Wald und Landschaft. Bern, Stuttgart, Wien, Haupt. 442 pp. Cabiddu, A., Branca, A., Dcandia, M., Pes, A., Santucci, P.M., Masoero, B., Calamari, L., 1999. Relationship between body condition score, metabolic profile, milk yield and milk composition in goats browsing a Mediterranean shrubland. Livest. Prod. Sci. 61, 267–273. Christen, R.E., Kunz, P.L., Langhans, W., Leuenberger, H., Sutter, F., Kreuzer, M., 1996. Productivity, requirements and efficiency of feed and nitrogen utilisation of grass-fed early lactating cows exposed to high Alpine conditions. J. Anim. Physiol. Anim. Nutr. 76, 22–35. Delucchi, M., 1993. Waldweide aus forstlicher Sicht. Bu¨ ndner Wald, Jahrgang 46 (1), 12–15. Dietl, W., 1990. Alpweiden naturgema¨ ss nutzen. Landfreund No. 11, Arbeitsgemeinschaft zur Fo¨ rderung des Futterbaus, Swiss Federal Research Station of Agronomy and Agroecology, Zurich-Reckenholz, Switzerland, p. 3. Dietl, W., Berger, P., Ofner, M., 1981. Die Kartierung des Pflanzenstandortes und der futterbaulichen Nutzungseignung von Naturwiesen: Eidg. Forschungsanstalt fu¨ r landwirtschaftlichen Pflanzenbau und Arbeitsgemeinschaft zur Fo¨ rderung des Futterbaues, Zu¨ rich-Reckenholz, Switzerland. Estermann, B.L., 2001. Nutrient cycling in suckler beef systems including alpine grazing. Breed and calving season effects and comparison with other livestock system options. ETH Dis-
sertation Thesis No. 14228, Wissenschaftsverlag Vauk Kiel KG, Kiel, Germany, 118 pp. Estermann, B.L., Wettstein, H.-R., Sutter, F., Kreuzer, M., 2001. Nutrient and energy conversion of grass-fed dairy and suckler beef cattle kept indoors or on high altitude pasture. Anim. Res. 50, 477–493. Estermann, B.L., Sutter, F., Schlegel, P.O., Erdin, D., Wettstein, H.R., Kreuzer, M., 2002. Effect of calf age and dam breed on intake, energy expenditure and excretion of nitrogen, phosphorus and methane of beef cows with calves. J. Anim. Sci. 80, 1124–1134. Ferna´ ndez-Martos y Bermu´ dez-Can˜ ete, C., 1961. La ganaderı`a y la repoblacion forestal en la Sierra Morena cordobesa. Montes 17, 139–143. Gonza´ lez Herna´ ndez, M.P., Silva-Pando, F.J., 1996. Grazing effects of ungulates in a Galician oak forest (northwest Spain). For. Ecol. Manage. 88, 65–70. Kie, J.G., Boroski, B.B., 1996. Cattle distribution, habitats, and diets in the Sierra Nevada of California. J. Range Manage. 49 (6), 482–488. Landau, S., Perevolotsky, A., Bonfil, D., Barkai, D., Silanikove, N., 2000. Utilisation of low quality resources by small ruminants in Mediterranean agro-pastoral systems: the case of browse and aftermath cereal stubble. Livest. Prod. Sci. 64 (1), 39–49. Malkama¨ ki, E., Haeggstro¨ m, C.-A., 1997. Short term impact of Finnish landrace cattle on the vegetation and soil of a wood pasture in SW Finland. Acta Bot. Fen. 159, 1–25. Malossini, F., Bovolenta, S., Piras, C., Ventura, W., 1995. Effect of concentrate on herbage intake and milk yield of dairy cows grazing an alpine pasture. Livest. Prod. Sci. 43, 119–128. Mayes, R.W., Lamb, C.S., Colgrove, M.P., 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agric. Sci. (Cambridge), 107, 161–170. Mertens, D.R., 1987. Prediction intake and digestibility using mathematical models of ruminal function. J. Anim. Sci. 64, 1548–1558. Naumann, K., Bassler, R., 1997. Die chemische Untersuchung von Futtermitteln, Methodenbuch, vol. 3. VdLUFA-Verlag, Darmstadt, Germany. Pordomingo, A.J., Rucci, T., 2000. Red deer and cattle diet composition in La Pampa, Argentina. J. Range Manage. 53, 649–654. RAP, 1999. Fu¨ tterungsempfehlungen und Na¨ hrwerttabellen fu¨ r Wiederka¨ uer (Swiss Federal Research Station for Animal Production). Landwirtschaftliche Lehrmittelzentrale, Zollikofen, Switzerland. Ro¨ sch, K., 1992. Einfluss der Beweidung auf die Vegetation des Bergwaldes. Forschungsbericht 26, Nationalpark Berchtesgaden, Germany, 100 pp. Sharrow, S.H., 1991. Tree planting pattern effects on forage production in a Douglas-fir agroforest. Agrofor. Syst. 16, 167–175. SPSS Inc., 1996. SYSTAT 6.0 for Windows. Statistics. Chicago, USA. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fibre, neutral detergent fibre, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3597. Walker, J.W., Heitschmidt, R.K., Dowhower, S.L., 1989. Some effects of a rotational grazing treatment on cattle preference for plant communities. J. Range Manage. 42 (2), 143–148.