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University of KwaZulu-Natal (1994)

Short-term effects of mixed grazing by cattle and sheep in highland sourveld.

Hardy, Mark Benedict.

Titre : Short-term effects of mixed grazing by cattle and sheep in highland sourveld.

Auteur : Hardy, Mark Benedict.

Université de soutenance : University of KwaZulu-Natal

Grade : Doctor of Philosophy (PhD) 1994

Résumé partiel
Data derived from a long-term grazing trial were used to determine short-term effects of mixed grazing by cattle and sheep in Highland Sourveld. Five cattle to sheep ratio treatments (viz. 1 :0, 3:1, 1 :1, 1 :3, 0:1) were applied, each at three stocking rates (viz. 0.5 (low), 0.71 (medium) and 1.0 (high) animal unit equivalents (AUE) ha¯¹). Ratios were expressed in terms of AUE cattle : AUE sheep. Stocking rate and ratio treatments were balanced at the start of each grazing season. Fourteen-month old Hereford steers and ’two-tooth’ Merino wethers were used as experimental animals. The trial comprised two components, viz. an animal production component and a simulated component. The animal production component was conducted only in the medium stocking rate treatment where the effect cattle to sheep ratio on the performance of cattle and sheep was determined for each of four grazing seasons (viz. 1989/90, four-paddock rotational grazing The low and high stocking rate 1990/91, 1991/92, 1992/93). A management system was applied. treatments were implemented by simulating a four-paddock rotational grazing system and using a single paddock for each stocking rate/ratio combination. Grazing of the simulated treatments coincided with the grazing of a specific ’test’ paddock in each ratio of the medium stocking rate treatment. These ’test’ paddocks and the simulated treatment paddocks were monitored to determine the impact of mixed grazing by cattle and sheep on individual grass plants and the sward. The whole of the experimental area was rested during the growing season prior to the start of the trial and all paddocks were burnt in the dormant season just before the start of the first grazing season. The trial therefore commenced with a with a uniform sward of immature herbage in all paddocks allocated to each group of animals. ln the second and subsequent growing seasons only those paddocks which had been rested in the previous season were burned prior to the onset of growth in early spring. Rainfall for the first three grazing seasons was similar to the long-term mean of 790mm whilst the last season was considered ’dry’ with 554mm recorded during 1992/93. In all grazing seasons, as the proportion of cattle in the species mix increased, sheep performance increased. A decline in sheep performance was recorded in each ratio treatment from the first to the third season


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