The performance of lambs on kikuyu as influenced by stocking rate and grazing system

Author: J.F. de Villiers, W.A. Botha and J.J. Wandrag
Year: 1994
Issue: 4
Volume: 24
Page: 133 - 139

Stocking rates of 20, 35 and 55 seven-month-old wethers/ha were used to determine the stocking rate/sheep performance relationship on kikuyu under continuous and rotational grazing, considering the stress placed on the animals by decreasing the availability of herbage with higher stocking rates. A total of 100 South African Mutton Merino and 80 Dohne Merino wether lambs were used over a period of three seasons in this study. A multiple regression analysis showed that stocking rate accounted for 58.3% (P ≤ 0.001), rainfall for 4.1 % (P ≤ 0.001) and grazing system for 0.8% (P ≤ 0.035) of the variation in ADG. Breed as an independent variable did not contribute significantly to the variation in ADG. The actual ADGs achieved by the wethers were 84 ± 3.47, 53 ± 4.97 and 13 ± 4.12 g/day for the lambs in the 20, 35 and 55 stocking rate and continuously grazed treatments while the lambs in the rotational system gained 80 ± 5.59, 40 ± 5.01 and 6 ± 3.98 g/day, respectively. In a multiple regression analysis, stocking rate accounted for I% (P ≤ 0.041), breed for 13.8% (P ≤ 0.001) and initial mass for 24.5% (P ≤ 0.001) of the variation in clean wool growth/day. For variation in fibre diameter, stocking rate accounted for 2.8% (P ≤ 0.001), initial mass for 18.3% (P ≤ 0.001), rainfall for 9.3% (P ≤ 0.001) and breed for 6.6% (P ≤ 0.001). A quadratic relationship (P ≤ 0.05) between the mean pre-grazing pasture height and ADG showed that maximum ADG in the rotational grazing system was at a pre-grazing disc-meter height reading of 16 cm. The predicted ADG at a disc-meter height of 16 cm was 97.8 (± 15.28) g/day. The quadratic relationship (P ≤ 0.05) between ADG and post-grazing pasture height showed that the turning point in mass gain was at about a 9-cm pasture height. A significant (P ≤ 0.05) linear relationship was found in the continuous grazing treatment between pasture height and ADG. The following linear relationships between ADG per animal (y) and stocking rate (x) were found: y = 124.3 – 2.03x and y = 118.3 – 2.08x with r-values of 0.794 (P ≤ 0.001) and 0.742 (P ≤ 0.001) for continuous and rotational grazing, respectively. Maximum gain/ha was achieved (optimum stocking rate) at 31 and 29 wethers/ha producing 1.902 and 1.782 kg/day for continuous and rota¬tional grazing, respectively. The daily livemass gains at these optimum stocking rates were 61.4 and 59.4 g/day, respec¬tively.

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Keywords: Average daily gain, final mass, sheep, wool growth
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