Partition of dietary energy and protein between fibre and other body components in fibre producing goats
The relationship between dietary nutrient inputs, particularly energy and protein, and their partition between fibre, meat and other non-meat components in British fibre producing goats was studied in a series of four experiments. Experiment 1 indicated that increasing dietary energy concentration from 10.2 to 11.9 MJ ME/kg dry matter (DM) significantly (P &'60 0.05 to 0.001) improved liveweight gain, feed conversion efficiency, carcass weight, cross sectional area of M.longissimus dorsi , and increased fat thickness over N.serratus dorsalis . Values were also increased in the carcass for dissected lean tissue and crude protein, weights and proportions of dissected and chemically extractable fat, weights of liver, kidneys and also fat deposition in the omental and perirenal plus retro-peritoneal depots. No consistent effects due to dietary energy inputs were observed for yield and diameter of mohair fibres. Similarly, changing the dietary protein concentration from 108 to 180 g/kg DM resulted in significantly (P &'60 0.05 to P &'60 0.001) increased values for live weight gain, DM intake, feed conversion efficiency, carcass weight, killing out proportions, area, width and depth of M.longissimus dorsi , weights of dissected carcass lean tissue, chemically determined crude protein and lipid in the carcass and also greater yield and diameter of mohair fibres. The results of experiment 2 indicated that increasing dietary protein concentrations (102, 126, 165, 185 g/kg DM) by the inclusion of fish and soya bean meal increased (linear effect, P &'60 0.05 to P &'60 0.001) live weight gain, feed conversion efficiency, carcass weight, width of M.longissimus dorsi , weight and proportion of dissectible carcass lean tissue and weight of crude protein in the carcass, liver and kidneys. The clean fibre yield and diameter were increased as the dietary CP concentration increased from 102 to 165 g/kg DM and then decreased at the highest CP concentration of 185 g/kg DM. Experiment 3 showed that source of nitrogen supplementation (urea, fish meal or soya bean meal) had no significant effects on growth rate, DM intake, feed conversion efficiency and nitrogen balance. However, soya bean meal supplementation resulted in significantly (P &'60 0.05 to P &'60 0.001) higher values for nitrogen digestibility, carcass weight, killing out proportion, dissectible lean tissue with trends to increase area of M.longissimus dorsi and microbial protein synthesis. The yield and diameter of mohair fibre were increased (P &'60 0.05) due to protein supplementation compared with the NPN supplementation in the diet. Experiment 4 indicated that average growth rate, DM intake, feed conversion efficiency, carcass weight and killing out proportions were not significantly different for the source of nitrogen supplementation (urea v fish meal) or for the genotype of Cashmere goats (Russian v Australasian crosses). Mid-side fleece growth (Cashmere &'43 guard hair) was significantly (P &'60 0.05) higher in goats given fish meal rather than urea supplemented diet and Russian goats tended to produce higher proportion of cashmere in the mid-side and in total fleece samples than those of Australasian genotype.