Sulfur supplementation of lupin grain diets fed to young sheep

Abstract

Summary. We examined the effects of supplementation of lupins with limestone or gypsum on liveweight change and wool production of young Merino wethers [age 10 months; starting liveweight (mean s.e.m.) 34.8 0.33 kg]. Lupins with the added compounds were fed in amounts estimated to provide metabolisable energy at 0.8, 1.0, 1.5 and 2.0 times maintenance requirements. The remainder of the ration was cereal straw fed at 10% of the weight of lupins given. Lupins coated with limestone or gypsum had a dry matter digestibility of 880 g/kg, and contained (g/kg DM) nitrogen 56.1 v. 57.4, sulfur 2.3 v. 4.6 and calcium 7.9 v. 5.4 respectively. As the amount of the ration fed was increased, there were linear increases (P<0.001) in liveweight gain (–9 to 226 g/day), clean wool growth rate (5.3–10.2 g/day), and fibre diameter of wool grown (18.0–21.6 m). There were no significant differences between lupins coated with limestone or gypsum in liveweight change (97 v. 105 g/day) or clean wool growth rate (7.6 v. 7.5 g/day). While the addition of sulfur to the diet reduced fibre diameter of wool grown (19.4 v. 20.0 m; P<0.01), this is not consistent with the effects of increased sulfur amino acid supply which would be expected to increase fibre diameter. It is concluded that the supply of inorganic sulfur to ruminal organisms was not limiting production responses to lupins or that there were other more limiting nutrients.