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DOI: https://doi.org/10.5713/ab.20.0821    [Accepted] Published online February 15, 2021.
Nitrogen metabolism and mammary gland amino acid utilization in lactating dairy cows with different residual feed intake
Yunyi Xie1  , Chao Miao1  , Yi Lu1  , Huizeng Sun1  , Jianxin Liu1,* 
Institute of Dairy Science, MOE Key Laboratory of Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou 310058, China
Correspondence:  Jianxin Liu, Tel: +86-571-88982097, Email: liujx@zju.edu.cn
Received: 6 December 2020   • Revised: 20 January 2021   • Accepted: 30 January 2021
Abstract
Objective
This study was conducted to enhance our understanding of nitrogen (N) metabolism and mammary amino acid (AA) utilization in lactating cows with divergent phenotypes of residual feed intake (RFI).
Methods
Fifty-three multiparous mid-lactation Holstein dairy cows were selected for RFI measurements over a 50-d experimental period. The 26 cows with the most extreme RFI values were classified into the high RFI (n =13) and low RFI (n =13) groups, respectively, for analysis of N metabolism and AA utilization.
Results
Compared with the high RFI cows, the low RFI animals had lower dry matter intake (P < 0.01) with no difference observed in milk yield between the two groups (P > 0.10). However, higher ratios of milk yield to dry matter intake (P < 0.01) were found in the low RFI cows than in the high RFI cows. The low RFI cows had significant greater ratios of milk protein to metabolizable protein (P = 0.02) and milk protein to crude protein intake than the high RFI cows (P = 0.01). The arterial concentration and mammary uptake of essential AA (P < 0.10), branched-chain AA (P < 0.10), and total AA (P < 0.10) tended to be lower in the low RFI cows. Additionally, the low RFI cows tended to have a lower ratio of AA uptake to milk output for essential AA (P = 0.08), branched-chain AA (P = 0.07) and total AA (P = 0.09) than the high RFI cows.
Conclusion
In summary, both utilization of metabolizable protein for milk protein and mammary AA utilization are more efficient in cows with lower RFI than in the high RFI cows. Our results provide new insight into the protein metabolic processes (related to N and AA) involved in feed efficiency.
Keywords: Amino Acid Metabolism; Mammary Gland; Nitrogen Metabolism; Residual Feed Intake
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