Diet selection and productivity of sheep grazing contrasting pastures

Abstract

A grazing experiment was conducted at the Big Ridge 2 site CSIRO, Chiswick (30˚31′S, 151˚39′E), 20 km south of Armidale, New South Wales, Australia. The site was established in 1955. In March 1966, phalaris and white clover were sown and pastures were fertilised annually with superphosphate until 1993. There were 3 pasture treatments, each with 2 replicates: degraded pasture (low phalaris content), phalaris-dominant, and phalaris–white clover. The effect of pasture type on animal production (liveweight gain and wool) was only significant in 1996, when there were large differences in pasture composition and production between the 3 pasture types. n-Alkane based estimates showed that pasture degradation affected diet selection and nutrient intake and thus sheep production. The estimates in this study also showed no clear preference for a single pasture species over time and lack of strong preferential selection for clovers when sheep were grazing 3 contrasting pastures. Preferential selection of a particular species varied over time depending on the presence and availability of alternative species. Although there were large differences in total N and S intake and faecal output between the 3 pastures, the proportion of the dietary nutrient used for production was similar. This observation reveals the importance of further improving pasture and grazing management, particularly in productive phalaris–white clover pasture with high nutrient flux, to improve nutrient recycling through plant uptake and retention by animals in the grazing ecosystem, and reduce losses.