Land Use Systems in Grassland Dominated Regions 587
Effects of the stocking rate on steer performance and vegetation patterns on mountain pastures
Troxler, J.1 and Chassot A.2
1Agroscope RAC Changins, Swiss Federal Agricultural Research Station, CH-1260 Nyon, Switzerland
2Agroscope Liebefeld-Posieux, Swiss Federal Agricultural Research Station, CH-1725 Posieux, Switzerland
Abstract
The new Swiss agricultural policy is leading to an expansion of extensively managed areas, especially in the mountain regions. Using these areas for extensive beef production might preserve an open landscape and favour biodiversity. A grazing experiment was conducted with steers on an unfertilised mountain pasture in the Swiss Jura from 2000 to 2003. The aim was to study the effects of a reduction of stocking rate (SR) on the growth of the animals and on the evolution of the vegetation. Three SR, high, medium and low (1.8, 1.2 and 0.6 animal unit (AU) per ha, respectively), were applied. Decreasing the stocking rate lead to a longer grazing period, to a higher daily gain per animal over the whole grazing season and finally to more than doubling the cumulative live weight gain (LWG) per animal. LWG per ha was highest at 1.2 AU ha-1 and lowest at 0.6 AU ha-1. The effect of a reduction of the SR on the botanical composition has been of limited extent up to now. At the end of the grazing season the amount of residual forage and its spatial variability were the largest in the low-SR treatment.
Keywords: Extensive grazing, beef, stocking rate, vegetation dynamics, mountain pasture, meat production
Introduction
As a consequence of increasing economic pressure on Swiss agriculture, marginal areas are threatened by abandonment, especially in the mountain regions. Using these areas for extensive beef production might preserve an open landscape and favour biodiversity.
A grazing experiment was conducted with steers on an unfertilised mountain pasture in the Swiss Jura to study the effects of a reduction of SR on the evolution of the vegetation and on the growth of the steers.
Materials and methods
The grazing experiment took place on a mountain pasture in the Swiss Jura that has not been fertilised since 1987 (Les Verrières, 1126 m asl, mean total precipitation from May to September: 675 mm, mean July temperature: 14.6 °C, vegetation dominated by Festuca rubra L. and Agrostis capillaris L.). No supplementary food was offered with the exception of minerals. The animals (crossbred steers Limousine x Red Pied) had no access to housing.
The experimental area was divided into 3 sections grazed at fixed SR of 1.8, 1.2 and 0.6 AU ha-1 (1 AU = 600 kg liveweight). Each section was subdivided into 3 paddocks, which were grazed in rotation.The animals were blocked by weight at turnout (approximately 400 kg) and randomly assigned to SR treatments.
The rotations were synchronized for the three groups of animals on the basis of grass offer at the highest SR. However, the first and the last rotations were not synchronized because start and end of the grazing period were set independently for each stocking rate, based on grass availability.
Grassland Science in Europe, Vol. 9 588
The animals were weighed at the beginning of each rotation and at the end of the grazing period. The evolution of the sward composition was measured in the springs of 2000 and 2002 along 30 fixed lines of 10 m, using the method described by Daget and Poissonet (1969). At the end of the grazing season, the residual dry matter yield was measured by cutting the remaining biomass at a height of 2 cm with electric shears. Six, 13 and 19 samples of 1 square meter each (0.10 m x 10 m) were taken at 1.8, 1.2 and 0.6 AU ha-1, respectively.
Results and discussion
The average cumulate liveweight gain (LWG) per animal is presented in figure 1. The initial average daily gains (ADG) were generally higher than 1000 g d-1 for all SR. This indicates adequate grass quality and quantity. As reported by Neuteboom et al. (1994), the herbage quality on unfertilised pastures is not necessarily a problem for animal growth in spring.
Nevertheless ADG decreased drastically in summer. At the highest SR, this can be explained by a shortage of grass on offer. At the two lower SR, however, this is rather due to a reduction of the grass quality, as shown by the large patches of senescent grass caused by the imbalance between grass demand and grass offer.
5.09 8.08
11.07 13.06
15.10
24.09
05.09
11.05 16.05 22.05 0 20 40 60 80 100 120 140 160 180
Cumulative LWG (kg animal-1)
11.06 17.07 13.08 16.09
18.09 17.10
26.08
15.0508.05 21.05
2001 2002
1.8 AU ha-1 1.2 AU ha-1 0.6 AU ha-1
5.09 8.08
11.07 13.06
15.10
24.09
05.09
11.05 16.05 22.05 0 20 40 60 80 100 120 140 160 180
Cumulative LWG (kg animal-1)
11.06 17.07 13.08 16.09
18.09 17.10
26.08
15.0508.05 21.05
2001 2002
1.8 AU ha-1 1.2 AU ha-1 0.6 AU ha-1
5.09 8.08
11.07 13.06
15.10
24.09
05.09
11.05 16.05 22.05 0 20 40 60 80 100 120 140 160 180
Cumulative LWG (kg animal-1)
11.06 17.07 13.08 16.09
18.09 17.10
26.08
15.0508.05 21.05
2001 2002
5.09 8.08
11.07 13.06
15.10
24.09
05.09
11.05 16.05 22.05 0 20 40 60 80 100 120 140 160 180
Cumulative LWG (kg animal-1)
11.06 17.07 13.08 16.09
18.09 17.10
26.08
15.0508.05 21.05 15.0508.05 21.05
2001 2002
1.8 AU ha-1 1.2 AU ha-1 0.6 AU ha-1 1.8 AU ha-1 1.2 AU ha-1 0.6 AU ha-1
Figure 1. Cumulative mean liveweight gain (LWG) per animal at three stocking rates during the grazing period in Les Verrières (1,126 m asl).
With decreasing SR from 1.8 to 0.6 AU ha-1, the length of the grazing season could be extended by 43 % and 69 % in 2001 and 2002, respectively. There was an extension of the grazing period both in spring and autumn. As a consequence, and combined with a higher ADG, the cumulative LWG per animal realised on the unfertilised mountain pasture was more than doubled in both years at 0.6 compared to 1.8 AU ha-1.
At the lowest SR the proportion of the main plant groups (grasses / legumes / herbs and weeds) did not change from 2000 to 2002 (Table 1). In this treatment, there was high spatial variability of grazing pressure. In the areas where the grazing pressure was very low, the proportion of some species, e.g., Festuca rubra, Dactylis glomerata and Ranunculus friesianus, increased between 2000 and 2002, whereas the opposite occurred for Cynosurus cristatus, Prunella vulgaris and Trifolium repens. At the higher SR treatments (medium and high), the proportion of grasses decreased in favour of both legumes and herbs.
Land Use Systems in Grassland Dominated Regions 589 Table 1. Evolution of the botanical composition from 2000 to 2002 at three stocking rates (Les Verrières, 1,126 m asl).
Stocking rate (600 kg AU ha-1)
High (1.8) Medium (1.2) Low (0.6)
Plant group 2000 2002 2000 2002 2000 2002
Grasses (%) 74 62 73 64 72 71
Legumes (%) 5 12 6 10 7 6
Herbs and weeds1 (%) 21 26 21 26 21 22
1Including Cyperaceae and Juncaceae.
The stocking rate had a marked effect on the amount and on the spatial variability of residual herbage at the end of the grazing period (Table 2). Both parameters were maximal at the lowest SR. Due to grass growth in autumn after the animals have been removed, the amount of residual herbage was higher at 1.8 than at 1.2 AU ha-1.
Table 2. Amount of residual herbage at the end of the grazing season (t DM ha-1) at three stocking rates in 2002 and 20031 (Les Verrières, 1,126 m asl; for the high SR, the values include grass growth after the animals have been removed on 26 August 2002 and 22 August 2003).
Stocking rate (600 kg AU ha-1) 2002 (24 October) 2003 (12 Sept. / 6 Oct.) t DM ha-1
High (1.8) 0.9 (0.6 – 1.9)2 0.6 (0.3 – 0.9)
Medium (1.2) 0.8 (0.1 – 1.5) 0.5 (0.1- 1.2)
Low (0.6) 1.2 (0.2 – 2.4) 1.3 (0.1 – 3.1)
1 Dates of measure in 2003: 12 September at the high and medium SR, 6 October at the low SR.
2 Values are means (minimum – maximum).
Conclusions
Up to now the reduction of the SR had a very little effect on the botanical composition of the sward. A reduction of the stocking rate had beneficial effects on the individual performance of the steers and on the duration of the grazing period.
This study tends to show that the extensive use of mountain pastures in Switzerland to fatten crossbred steers can be an interesting alternative to abandonment of these areas.
References
Daget P. and Poissonet J. (1969) Analyse phytologique des prairies. Applications agronomiques. Document N° 48. CNRS. Montpellier.
Neuteboom J.H., ‘t Mannetje L., Lantinga E.A. and Wind K. (1994) Cattle weight changes and botanical composition of an unfertilised grass sward under continuous grazing. In: Proceedings of the 15th General meeting of the European Grassland Federation, 320-323.
