Xie Yunyi, Wu Zezhong, Wang Diming, Liu Jianxin
Institute of Dairy Science, MOE Key Laboratory of Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 People's Republic of China.
J Anim Sci Biotechnol. 2019 Jun 14;10:54. doi: 10.1186/s40104-019-0356-3. eCollection 2019.
Residual feed intake (RFI) is an inheritable measure of feed efficiency that is independent on level of production. However, physiological and metabolic mechanisms underlying divergent RFI are not fully elucidated. This study was conducted to investigate dietary nitrogen (N) partitioning and microbial protein synthesis in lactating dairy cows divergent in phenotypic RFI.
Thirty Holstein dairy cows (milk yield = 35.3 ± 4.71 kg/d; milk protein yield = 1.18 ± 0.13 kg/d; mean ± standard deviation) were selected for the experiment to derive RFI. After the RFI measurement period of 50 d, the 10 lowest RFI cows and 8 highest RFI cows were selected. The low RFI cows had lower dry matter intake (DMI, < 0.05) than the high RFI cows, but they produced similar energy-corrected milk. The ratios of milk to DMI (1.41 vs. 1.24, < 0.01) and energy-corrected milk to DMI (1.48 vs. 1.36, < 0.01) were greater in low RFI cows than those in the high RFI cows. The low RFI cows had lower milk urea nitrogen than that in the high RFI cows ( = 0.05). Apparent digestibility of nutrients did not differ between two groups ( > 0.10). Compared with high RFI animals, the low RFI cows had a lower retention of N (5.72 vs. 51.4 g/d, < 0.05) and a higher partition of feed N to milk N (29.7% vs. 26.5%, < 0.05).
The results suggest that differences in N partition, synthesis of microbial protein, and utilization of metabolizable protein could be part of the mechanisms associated with variance in the RFI.
剩余采食量（RFI）是一种与生产水平无关的可遗传的饲料效率衡量指标。然而，RFI差异背后的生理和代谢机制尚未完全阐明。本研究旨在调查表型RFI不同的泌乳奶牛的日粮氮（N）分配和微生物蛋白质合成情况。
选择30头荷斯坦奶牛（产奶量 = 35.3 ± 4.71 kg/d；乳蛋白产量 = 1.18 ± 0.13 kg/d；均值 ± 标准差）进行实验以得出RFI。在50天的RFI测量期后，挑选出10头RFI最低的奶牛和8头RFI最高的奶牛。低RFI奶牛的干物质摄入量（DMI，< 0.05）低于高RFI奶牛，但它们产的能量校正乳量相似。低RFI奶牛的奶与DMI的比值（1.41对1.24，< 0.01）和能量校正乳与DMI的比值（1.48对1.36，< 0.01）高于高RFI奶牛。低RFI奶牛的乳尿素氮含量低于高RFI奶牛（ = 0.05）。两组之间营养物质的表观消化率无差异（> 0.10）。与高RFI动物相比，低RFI奶牛的氮保留量较低（5.72对51.4 g/d，< 0.05），饲料氮向乳氮的分配比例较高（29.7%对26.5%，< 0.05）。
结果表明，氮分配、微生物蛋白质合成和可代谢蛋白质利用的差异可能是与RFI差异相关机制的一部分。
