Koch A R, Kromann R P, Wilson T R
J Nutr. 1979 Mar;109(3):426-36. doi: 10.1093/jn/109.3.426.
The growth of body protein, fat, and skeleton of growing steers was determined from published experimental data of steers fed three planes of nutrition. Each animal was partitioned into: 1) metabolically slow tissue which included hide, hooves, horns, skeleton, and fat, and 2) metabolically active tissue (MAT) which were the remaining tissues. MAT grew exponentially in time and approached the same final value for all planes of nutrition; however, growth rates depended on energy intake. The mass of active tissues was described by MATkg = 27 + 393 (1 - e-t/tau) where t and tau are in months; tau was 25.8, 46.7, and 57.4 months for the high, medium, and low planes of nutrition, respectively. The finding that MAT retained the same mathematical form but grew more slowly on the lower nutritional planes suggests that changes in energy set the scale of physiological age. Fat deposition was linear with time for all groups, although the rates depended on energy intake. The rates were 8.21, 2.08, and 1.29 kg/month for the high, mediu, and low planes of nutrition, respectively. The results suggest that steers are not programmed to synthesize protein first and then fat only with the remaining energy; rather the level of energy intake and the age determine how the ingested energy is partitioned into protein and fat synthesis.
根据已发表的针对处于三个营养水平的生长阉牛的实验数据，测定了生长阉牛的体蛋白、脂肪和骨骼的生长情况。每头动物被分为：1）代谢缓慢组织，包括皮肤、蹄、角、骨骼和脂肪；2）代谢活跃组织（MAT），即其余组织。MAT随时间呈指数增长，并且在所有营养水平下都接近相同的最终值；然而，生长速率取决于能量摄入量。活跃组织的质量由MATkg = 27 + 393 (1 - e-t/tau) 描述，其中t和tau以月为单位；对于高、中、低营养水平，tau分别为25.8、46.7和57.4个月。MAT在较低营养水平下保持相同的数学形式但生长较慢这一发现表明，能量变化设定了生理年龄的尺度。所有组的脂肪沉积随时间呈线性变化，尽管速率取决于能量摄入量。高、中、低营养水平下的速率分别为8.21、2.08和1.29千克/月。结果表明，阉牛并非先被设定为合成蛋白质，然后仅将剩余能量用于合成脂肪；相反，能量摄入水平和年龄决定了摄入的能量如何分配到蛋白质和脂肪合成中。
