Complementary selection and intake of annual pastures by sheep and goats

Abstract

The compositions of diets of Merino sheep and Angora goats were determined when they grazed annual pastures (Wimmerarye Lolium rigidum; Barley grass, Hordeum leporinum; Silver grass, Vulpia bromoides; Subterranean clover, Trifolium subterraneum) in March, May, August and October, 1985 and in February and April, 1987. Oesophageally-fistulated sheep and goats were stocked at 7.5 and 10/ha on pastures with 1.7–2.9 t available DM/ha in 1985, 3.0–4.5 t/ha in 1987. On all occasions, both species selected a diet with more green herbage, N and digestible organic matter than on offer in the pasture. Except in February, sheep selected a diet with more green clover, less green grass and dry herbage, higher in N (3.3–3.9% vs. 2.8–3.4%) and lower in ADF (24–39% vs. 27–44%), than did goats; differences were significant except in February and March when 98% and 93% of available pastures were dry herbage. In vitro OM digestibilities, about 40% in February and at least 68% in March, April, August and October, did not differ between sheep and goats. In May, goats selected a diet of 66% dead herbage vs. 20% for sheep, 44% ADF vs. 29%, 1.7% N vs. 3.3% and in vitro digestibility was 12% lower (P<0.05). Intakes were calculated in February, March, April and October from digestibility estimates and total collection of faeces. Goats consumed 10% less DM/kg LW in February (NS), 40% more in March (P<0.001), 23% more in April (NS), 60% more in October (P<0.001). Intake of N (g/day) did not differ between species by more than 11% on any occasion (NS). Except in February for both species and for goats in May, both species selected diets with high OM digestibilities and N intakes considerably above requirements while consuming quite different combinations of green grass, green clover and dead herbage. Hence, on these pastures, sheep and goats will obtain their nutrient requirements, when possible, if stocked at the same rate and managed similarly.