Abstract: [Objective] This study aimed to investigate the effects of dietary supplementation with methionine dipeptide on milk yield, milk composition, and milk protein production in dairy cows, providing experimental evidence for the application of methionine dipeptide in dairy farming. [Method] A total of 120 healthy Chinese Holstein cows were selected as experimental animals and randomly divided into a control group and a treatment group, with 60 cows per group and 5 replicates per group. The control group was fed a conventional basal diet, while the treatment group received the basal diet supplemented with 50.0 mg/kg of methionine dipeptide. The experimental period lasted 70 days. During the experiment, milk yield, feed-to-milk ratio, somatic cell count, and milk protein content were measured for both groups. [Result] The treatment group showed a significantly lower feed-to-milk ratio compared to the control group （P<0.05）, and the average daily milk yield and peak milk yield were highly significantly higher than those of the control group （P<0.01）. The milk protein percentage in the treatment group was increased by 30.77% compared to the control group （P<0.01）, while somatic cell count was reduced by 75.79% （P<0.01）. The content of β-lactoglobulin in milk was significantly increased（P<0.05）,and the contents of α-casein, β-casein, lactoferrin, and immunoglobulin were highly significantly increased （P<0.01）. The κ-casein content was highly significantly lower than that of the control group （P<0.01）. No significant differences were observed between the two groups in milk urea nitrogen, lactose, milk solids, or milk fat content （P>0.05）. [Conclusion] Supplementation of the basal diet with 50.0 mg/kg of methionine dipeptide can significantly enhance the lactation performance of dairy cows, improve milk quality, increase milk protein-related indicators, and reduce somatic cell count in milk, thereby exerting a positive effect on the healthy management of dairy cows.

Key words: methionine dipeptide, dairy cows, milk yield, milk composition, milk protein