Institute of Livestock and Grassland Science, NARO, Tochigi, Japan.
Anim Sci J. 2021 Jan-Dec;92(1):e13562. doi: 10.1111/asj.13562.
The objective of this experiment was to investigate the effects of low-crude protein (CP) diets supplemented with rumen-protected lysine and methionine on growth performance, nitrogen excretion, and carcass traits in Holstein steers. Steers consumed the following diets: (1) 17.2% CP on a dry-matter basis during the early period (from 7 to 10 months of age) and 14.5% CP during the late period (from 10 to 18 months of age; CON, n = 4, initial body weight [BW] 238 kg), and (2) 14.4% CP during the early period and 11.4% CP during the late period (AA, n = 4, initial BW 243 kg). The AA diet contains rumen-protected lysine and methionine. Except for CP intake, feed intake and body weight gain were not affected by dietary CP content. Total nitrogen excretion per metabolic BW tended to be lower (p < .10) in the early period and significantly lower (p < .05) in the late period with decreasing the feed CP content. Plasma urea nitrogen concentrations were lower in AA than CON. Carcass traits and total free amino acid contents of the longissimus thoracis muscle were not affected by dietary CP content. Adding rumen-protected lysine and methionine to a low-CP diet would reduce nitrogen excretion in fattening Holstein steers without affecting productivity.
本实验旨在研究低粗蛋白（CP）日粮添加保护性赖氨酸和蛋氨酸对荷斯坦育肥牛生长性能、氮排泄和胴体特性的影响。试验牛分别饲喂以下日粮：（1）生长期（7-10 月龄）日粮 CP 水平为 17.2%，育肥期（10-18 月龄）日粮 CP 水平为 14.5%（CON，n=4，初始体重 238kg）；（2）生长期日粮 CP 水平为 14.4%，育肥期日粮 CP 水平为 11.4%（AA，n=4，初始体重 243kg）。AA 日粮添加保护性赖氨酸和蛋氨酸。除 CP 摄入量外，日粮 CP 含量对采食量和体重增重无影响。随着饲粮 CP 含量的降低，代谢 BW 的总氮排泄量在生长期呈下降趋势（p<0.10），在育肥期显著下降（p<0.05）。AA 组血浆尿素氮浓度低于 CON 组。日粮 CP 含量对背最长肌胴体特性和游离氨基酸总量无影响。在 CP 水平较低的日粮中添加保护性赖氨酸和蛋氨酸可以减少育肥牛的氮排泄，而不会影响生产性能。
