Milk replacers containing soybean protein isolates or concentrates: nitrogen digestibility and utilization by preruminant lambs

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Abstract
Preruminant male crossbred lambs, aged 2-5 days at the start of the experiment, were given milk replacers containing between 0.25 and 0.29 of the total energy as protein. A comparison of milk replacers containing either soybean isolates or concentrates as the sole source of protein showed that, while the apparent digestibilities of dry matter and nitrogen were significantly higher for diets containing isolates, the efficiencies of retention of the apparently digested nitrogen were significantly higher for the concentrate diets. The net result was no significant difference in nitrogen balance between the diets. The milk replacers were accepted readily by the lambs, and intakes of gross energy of up to three times the maintenance requirement were attained without difficulty. Nitrogen balances of lambs given a milk replacer based on a soybean concentrate were not significantly improved by supplementation of the diet with lysine, in addition to methionine. Similarly, the nitrogen balances of lambs given a soybean isolate-based milk replacer, plus methionine, were unaffected when one of five supplementary amino acids (Lys, Thr, Val, Isol, Leu) was omitted in turn from the diet.