The Performance and Carcass Fat Characteristics of Lambs Fattened on Concentrate Diets: 1. Effects of Maize and Barley as the Cereal Source and of Dietary Supplementation with Roughage, Vitamin E, Cobalt and Vitamin B

In a 2 × 2 factorial experiment, 24 early-weaned lambs were fed for 10 weeks a concentrate unpelleted diet containing either barley or maize as the sole cereal source, with or without a supplement of vitamin E. Liveweight gain and killing-out percentage of the lambs were similar on all treatments, while feed intake and feed conversion ratio were lower on the maize diets. In rumen fluid the pH was lower, total VFA concentration higher and the ratio of acetate to propionate lower on the maize than on the barley diets, while vitamin E supplement had no effect. The melting points of perinephric and subcutaneous fat of the lambs were relatively low compared with those for lambs fattened off grass, associated with relatively high levels of oleic acid and low levels of stearic acid. Levels of total odd-numbered n-acids and of branched-chain fatty acids in both fats were not unusually high. In a second experiment the effects of supplementing a barley-based concentrate diet with 10% oat hulls with or without cobalt sulphate at 3.75 mg/kg diet or vitamin B₁₂ at 0.15 mg/kg were studied using 24 early-weaned lambs. Oat hulls reduced liveweight gain, but cobalt or vitamin B₁₂ had no effect on the performance of the lambs. Oat hulls did not affect the pH or VFA proportions in the rumen fluid except for a small increase in isobutyric acid, while cobalt and vitamin B₁₂ increased the proportion of acetic acid. Oat hulls did not affect the melting point or fatty acid composition of subcutaneous or perinephric fat of the lambs except for a slight reduction in the level of linoleic acid in subcutaneous fat. Cobalt increased the level of stearic acid in subcutaneous fat; otherwise cobalt and vitamin B₁₂ did not affect the melting point or fatty acid composition of either fat. The levels of total odd-numbered and branched-chain fatty acids in the subcutaneous fat were not unusally high.