Qin Xiaoli, Lin Xueyan, Hanigan Mark D, Zhao Kai, Hu Zhiyong, Wang Yun, Hou Qiuling, Wang Zhonghua
Ruminant Nutrition and Physiology Laboratory, College of Animal Science and Technology, Shandong Agricultural University, Tai'an 271018, China.
Department of Dairy Science, Virginia Tech, Blacksburg, VA 24061, USA.
Animals (Basel). 2025 Apr 24;15(9):1210. doi: 10.3390/ani15091210.
This study evaluated the effects of supplementing rumen-protected methionine, threonine, isoleucine, and leucine to low-protein diets on lactating dairy cow performance. Sixty Holstein cows were assigned to one of four dietary treatments in a 9-week randomized complete block design: positive control (16% crude protein diet; 16% CP), negative control (12% CP), 12% CP plus the four essential amino acids (12% CP + EAA), and 14% CP supplemented with the four EAA (14% CP + EAA). The milk protein yield was significantly decreased in the 12% CP group compared to the 16% CP group but was restored to comparable levels with EAA supplementation of both the 12% and 14% CP diets. Dietary nitrogen intake and urinary nitrogen excretion both increased with higher dietary CP levels. Nitrogen utilization efficiency in milk was significantly improved by EAA supplementation, with the highest efficiency observed in the 12% CP + EAA treatment (39.0% vs. 33.3% in the 16% CP diet). Plasma urea levels increased with elevated dietary CP and EAA supplementation. Moreover, EAA supplementation significantly elevated venous methionine levels and showed a tendency to increase venous leucine levels. Additionally, compared to the negative control, EAA supplementation increased concentrations of glucagon and prolactin ( < 0.05). EAA supplementation of low-protein diets, particularly the 14% CP diet, improved the dietary protein efficiency of lactating cows without a concomitant decrease in milk protein yield.
本研究评估了在低蛋白日粮中补充瘤胃保护蛋氨酸、苏氨酸、异亮氨酸和亮氨酸对泌乳奶牛生产性能的影响。采用9周随机完全区组设计，将60头荷斯坦奶牛分配到四种日粮处理之一：正对照组（16%粗蛋白日粮；16%CP）、负对照组（12%CP）、12%CP加四种必需氨基酸（12%CP + EAA）和14%CP加四种必需氨基酸（14%CP + EAA）。与16%CP组相比，12%CP组的乳蛋白产量显著降低，但通过在12%和14%CP日粮中补充EAA可恢复到相当水平。日粮粗蛋白水平越高，日粮氮摄入量和尿氮排泄量均增加。补充EAA显著提高了牛奶中的氮利用效率，在12%CP + EAA处理中观察到最高效率（16%CP日粮中为39.0%对33.3%）。血浆尿素水平随日粮粗蛋白和EAA补充量的增加而升高。此外，补充EAA显著提高了静脉蛋氨酸水平，并显示出增加静脉亮氨酸水平的趋势。另外，与负对照组相比，补充EAA增加了胰高血糖素和催乳素的浓度（P<0.05）。在低蛋白日粮中补充EAA，尤其是14%CP日粮，提高了泌乳奶牛的日粮蛋白质效率，同时乳蛋白产量没有相应下降。
