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Effects of Supplementing Rumen-Protected Lysine and Methionine on Apparent Digestibility, Rumen Fermentation Parameters, and Microbial Profiles in Lactating Dairy Cows Under Different Environmental Conditions
by
, , , and
Ruoran Tao
1
,
Ke Wang
1,
Xing Han
1,
Xu Tang
1,
Dian Wang
2,3,
Yuhang Ding
4,
Yuhong Ma
1,
Maocheng Jiang
1,
Sijia Liu
1,
Yinghao Huang
1,
Caiyun Fan
1,
Zhao Zhuo
1 and
Jianbo Cheng
1,* 1
College of Animal Science and Technology, Anhui Agricultural University, Hefei 230036, China
2
National Center of Technology Innovation for Dairy, Hohhot 010010, China
3
Inner Mongolia Youran Dairy Group Limited, Hohhot 010010, China
4
Shanghai Menon Biotechnology Co., Ltd., Shanghai 201800, China
*
Author to whom correspondence should be addressed.
Animals 2025, 15(23), 3439; https://doi.org/10.3390/ani15233439 (registering DOI)
Submission received: 24 October 2025
/
Revised: 20 November 2025
/
Accepted: 26 November 2025
/
Published: 28 November 2025
(This article belongs to the Special Issue Phytochemicals and Feed Additives in Ruminant Nutrition: Effects on Health, Microbiota, and Methane Emissions)
Simple Summary
Thirty lactating Holstein dairy cows were randomly assigned in a paired design to evaluate the effects of a basal diet (CON) versus the same basal diet supplemented with 60 g/d rumen-protected lysine and 30 g/d of rumen-protected methionine (RPLM) under both heat stress (HS) and non-heat stress (NHS) conditions. Supplementation with RPLM significantly improved the apparent digestibility of dry matter, crude protein, and neutral detergent fiber. During the HS period, rumen ammonia nitrogen concentration decreased, while concentrations of TVFA, acetate, and butyrate increased markedly. 16S rRNA sequencing analysis revealed that RPLM supplementation enriched butyrate-producing bacterial taxa, particularly the NK4A214_group, which showed a positive correlation with nutrient digestibility. These findings indicate that RPLM enhances rumen microbial structure and nutrient utilization efficiency, thereby mitigating heat stress-induced digestive impairments.
Abstract
This study investigated the effects of supplementing rumen-protected lysine (RPL; 60 g/d) and methionine (RPM; 30 g/d) on nutrient digestibility, rumen fermentation, and microbial composition in 30 early-lactation Holstein dairy cows under both heat stress (HS) and non-heat stress (NHS) conditions. Cows were paired based on parity, milk yield, and body weight, and then assigned to one of two dietary treatments: the control group (CON), receiving the basal diet only, or the RPLM group, which received the basal diet supplemented with 60 g/d of RPL and 30 g/d of RPM (n = 15 per group). All animals underwent a transition from HS to NHS conditions during the experimental period, allowing for within-animal comparison across thermal environments. Results demonstrated that RPLM supplementation significantly improved the apparent digestibility of dry matter (DM), crude protein (CP), and neutral detergent fiber (NDF) (p < 0.05), with a significant treatment × environment interaction observed for DM digestibility (p < 0.01). Under HS conditions, RPLM reduced ruminal NH3-N concentration (p < 0.05) and increased total volatile fatty acids (TVFA), acetate, and butyrate levels (p < 0.01), suggesting enhanced nitrogen utilization and energy metabolism. No significant effects were observed on ruminal pH or the acetate-to-propionate ratio. 16S rRNA sequencing revealed that RPLM supplementation increased the relative abundance of fiber-degrading and butyrate-producing taxa, including NK4A214_group, Christensenellaceae_R-7_group, norank_f__Muribaculaceae, and norank_f__F082. These microbial taxa exhibited strong positive correlations with DM and CP digestibility (p < 0.001). LEfSe analysis further confirmed their status as key microbial biomarkers in the RPLM-NHS group. Collectively, concurrent supplementation of RPL and RPM modulates the ruminal microbiota, alleviates HS-induced reductions in digestive efficiency, and enhances overall nutrient utilization in dairy cows.
