Gerrits W J, Schrama J W, Tamminga S
Animal Nutrition Group, Wageningen Institute of Animal Sciences (WIAS), Wageningen Agricultural University, 6700 AH, Wageningen, The Netherlands.
J Nutr. 1998 Oct;128(10):1774-85. doi: 10.1093/jn/128.10.1774.
A previous study showed that the marginal efficiency of utilization of digestible nitrogen for deposition in the body in preruminant calves is only approximately 30%. The study consisted of two similar experiments that were performed in two live weight ranges: 80-160 and 160-240 kg. In each experiment, 36 calves were allotted to one of twelve dietary treatments, consisting of six protein intake levels at each of two protein-free energy intake levels. This paper presents amino acid analyses of dietary and body proteins of these experiments with the following goals: 1) to identify possible limiting indispensable amino acids, and 2) to quantify the effect of protein and energy intake on the amino acid composition of deposited body proteins. The marginal efficiency of utilization of ileal digestible amino acids for deposition in the body did not exceed 30% for any of the indispensable amino acids. Increasing protein intake increased the ratio of indispensable to dispensable amino acids in deposited body proteins, likely caused by an increase in muscle-to-bone ratio in the carcass with a concomitant decrease in the proportion of collagen protein. It was concluded that the low marginal efficiency of utilization of digestible milk proteins for growth in preruminant calves of this weight range was not caused primarily by a severe limitation of a single indispensable amino acid in the diet.
先前的一项研究表明，反刍前犊牛体内可消化氮沉积的利用边际效率仅约为30%。该研究包括在两个体重范围内进行的两个相似实验：80 - 160千克和160 - 240千克。在每个实验中，36头犊牛被分配到十二种日粮处理中的一种，每种处理包括两种无蛋白能量摄入水平下的六个蛋白质摄入水平。本文介绍了这些实验中日粮和体蛋白的氨基酸分析，目标如下：1）确定可能的限制性必需氨基酸，2）量化蛋白质和能量摄入对沉积体蛋白氨基酸组成的影响。对于任何必需氨基酸，回肠可消化氨基酸沉积在体内的利用边际效率均未超过30%。增加蛋白质摄入量会提高沉积体蛋白中必需氨基酸与非必需氨基酸的比例，这可能是由于胴体中肌肉与骨骼比例增加，同时胶原蛋白比例下降所致。得出的结论是，在这个体重范围内的反刍前犊牛中，可消化乳蛋白用于生长的低利用边际效率主要不是由日粮中单一必需氨基酸的严重限制引起的。
