Gerrits W J, France J, Dijkstra J, Bosch M W, Tolman G H, Tamminga S
Wageningen Institute of Animal Sciences, Wageningen Agricultural University, The Netherlands.
J Nutr. 1997 Jun;127(6):1243-52. doi: 10.1093/jn/127.6.1243.
In a companion paper, a mechanistic model is described, integrating protein and energy metabolism in preruminant calves of 80-240 kg live weight. The model simulates the partitioning of nutrients from ingestion through intermediary metabolism to growth, consisting of accretions of protein, fat, ash and water. The model also includes a routine to check possible dietary amino acid imbalance and can be used to predict amino acid requirements. This paper describes a sensitivity and behavioral analysis of the model, as well as tests against independent data. Increasing the carbohydrate:fat ratio at equal gross energy intakes leads to higher simulated protein- and lower simulated fat-deposition rates. Simulation of two experiments, not used for the development of the model, showed that rates of gain of live weight, protein and fat were predicted satisfactorily. The representation of protein turnover enables the investigation of the quantitative importance of hide, bone and visceral protein in protein and energy metabolism. The model is highly sensitive to 25% changes in kinetic parameters describing muscle protein synthesis and amino acid oxidation. Comparing simulated with experimentally derived amino acid requirements shows agreement for most amino acids for calves of approximately 90 kg live weight. For calves of approximately 230 kg live weight, however, lower requirements for lysine and for methionine+cystine are suggested by the model. More attention has to be paid to the inevitable oxidative losses of amino acids. It is concluded that the model provides a useful tool for the development of feeding strategies for preruminant calves in this weight range.
在一篇配套论文中，描述了一个机理模型，该模型整合了体重80 - 240千克反刍前犊牛的蛋白质和能量代谢。该模型模拟了营养物质从摄入通过中间代谢到生长的分配过程，生长包括蛋白质、脂肪、灰分和水分的积累。该模型还包含一个检查日粮氨基酸可能不平衡的程序，可用于预测氨基酸需求。本文描述了该模型的敏感性和行为分析，以及与独立数据的对比测试。在总能量摄入量相等的情况下，提高碳水化合物与脂肪的比例会导致模拟的蛋白质沉积率升高，而模拟的脂肪沉积率降低。对两个未用于模型开发的实验进行模拟，结果表明体重、蛋白质和脂肪的增重率预测结果令人满意。蛋白质周转的表示方法能够研究皮、骨和内脏蛋白质在蛋白质和能量代谢中的定量重要性。该模型对描述肌肉蛋白质合成和氨基酸氧化的动力学参数25%的变化高度敏感。将模拟的氨基酸需求与实验得出的氨基酸需求进行比较，结果表明，对于体重约90千克的犊牛，大多数氨基酸的模拟结果与实验结果一致。然而，对于体重约230千克的犊牛，该模型表明其对赖氨酸和蛋氨酸+胱氨酸的需求较低。必须更加关注氨基酸不可避免的氧化损失。得出的结论是，该模型为制定此体重范围内反刍前犊牛的饲养策略提供了一个有用的工具。
