The utilization by preruminant lambs of milk replacers containing isolated soya bean protein

Fifty-nine male crossbred lambs, aged 2-5 days at the start of the experiment, were used in four experiments to compare the nutritive value of isolated soya bean protein (ISP) (Promine D) with cows' milk protein (DSM) in milk replacer diets. In experiment 1, ISP diets of low (0.10 of total energy as protein) or medium protein content (0.25 protein energy) with or without supplements of DL-methionine, were compared with DSM diets. In experiment 2, graded amounts of DL-methionine were added to the medium protein ISP diet to determine the optimum level of supplementation. In experiment 3, butter oil, groundnut oil, medium chain triglycerides (MCT) and coconut fat were added as the sole sources of fat in low protein ISP diets and compared with DSM diets that contained butter oil or groundnut oil. In experiment 4 alginates were added to a low protein ISP diet to improve the suspendibility of ISP in the milk replacer. The addition of DL-methionine consistently improved nitrogen balances of the lambs. The optimum concentration of methionine plus cystine in the medium protein ISP diet was 29.8 2 7.9 mg per 100 KJ, compared with 22.5 mg/100 KJ in the unsupplemented ISP diet. Low protein ISP diets that contained groundnut oil as the sole source of fat were poorly accepted and poorly utilized. The apparent digestibilities of butter oil (0.950) and MCT (0.958) were significantly higher than those of either coconut fat (0.852) or groundnut oil (0.770). Comparable values for DSM diets were: butter oil, 0.985; groundnut oil, 0.855. The addition of alginates to the medium protein ISP diet prevented the ISP from settling out, but was associated with a reduced intake of the diet, a reduction in nitrogen digestibility and an increase in the moisture content of the faeces. The nitrogen balances of lambs given DSM diets were always higher than those of comparable lambs given ISP diets.