Keith M O, Bell J M
Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada.
Proc Soc Exp Biol Med. 1989 Mar;190(3):246-53. doi: 10.3181/00379727-190-42856.
Reasons for differences in growth of weanling mice fed different blends of purified proteins in diets apparently adequate in indispensable amino acids were investigated. Dietary nitrogen provided at increasing levels from a mixture of casein, gelatin, and zein, or from these plus gliadin and lactalbumin resulted in similar weight gains and efficiency of feed utilization in weanling mice. These responses were always lower (P less than 0.05) than for mice fed the control diet. When diets were based on true digestible nitrogen and amino acids, weight gains and feed efficiency decreased (P less than 0.05) as the dietary nitrogen level increased. High plasma glycine concentrations and high phenylalanine to tyrosine ratios were associated with high dietary glycine levels provided by gelatin. When a mixture of constant proportions of protein sources, predominantly casein, supplied most of the dietary nitrogen, small increases in weight gains and feed efficiency were observed as the nitrogen level in the diet increased. Varying the proportions of sources, which increased the percentage of gelatin, resulted in decreased gains in response to more dietary nitrogen. Replacing the amino acids found in gelatin by crystalline L-amino acids and replacing glycine by glutamic acid improved gains and feed efficiency (P less than 0.05) compared with gelatin-containing diets. These studies demonstrated that glycine at dietary concentrations of approximately 1-2%, either from gelatin or as the free amino acid, inhibited growth and feed utilization of growing mice.
研究了在必需氨基酸明显充足的日粮中，用不同纯化蛋白质混合物喂养断奶小鼠时生长差异的原因。酪蛋白、明胶和玉米醇溶蛋白的混合物，或这些蛋白加上醇溶谷蛋白和乳白蛋白，以递增水平提供日粮氮，断奶小鼠的体重增加和饲料利用效率相似。这些反应总是低于（P小于0.05）喂食对照日粮的小鼠。当日粮以真可消化氮和氨基酸为基础时，随着日粮氮水平的增加，体重增加和饲料效率下降（P小于0.05）。高血浆甘氨酸浓度和高苯丙氨酸与酪氨酸比值与明胶提供的高日粮甘氨酸水平有关。当恒定比例的蛋白质来源混合物（主要是酪蛋白）提供大部分日粮氮时，随着日粮中氮水平的增加，体重增加和饲料效率有小幅提高。改变来源比例，增加明胶的百分比，会导致对更多日粮氮的反应中体重增加减少。与含明胶日粮相比，用结晶L-氨基酸替代明胶中的氨基酸并用谷氨酸替代甘氨酸可提高体重增加和饲料效率（P小于0.05）。这些研究表明，日粮中约1-2%浓度的甘氨酸，无论是来自明胶还是作为游离氨基酸，都会抑制生长小鼠的生长和饲料利用。
