A hierarchical 3-level meta-analysis of the effect of arginine supplementation on lactational performance in dairy cows and the associated influencing factors.

Arginine is one of the most versatile among the AA because of its important role in multiple functions of the body. However, the effect of Arg supplementation on lactational performance in dairy cows, and the associated influencing factors, have not been well characterized. Weighted mean differences (WMD) of continuous variables from 14 articles published by March 31, 2025, were pooled by random-effects models using the Stata version 17 to explore the details regarding Arg application in dairy cows. Results showed that Arg supplementation increased milk yield (WMD = 1.29 kg/d, [95% CI: 0.58, 1.99]), milk protein yield (WMD = 0.04 kg/d, [95% CI: 0.00, 0.07]), and milk fat yield (WMD = 0.06 kg/d, [95% CI: 0.02, 0.10]) with significant heterogeneities (Varlevel1 < 75%), but had no overall effects on DMI, milk protein concentration, milk fat concentration, lactose yield, and lactose concentration. Moderator analysis revealed that the positive effects of Arg supplementation on milk yield, milk protein yield, and milk fat yield were more prominent in dairy cows in early lactation or being fed an MP-adequate diet or corn silage-based diet. Compared with feeding rumen-protected Arg, Arg supplementation through infusion increased the milk yield (WMD = 1.21 kg/d, [95% CI: 0.48, 1.95]) and had a tendency to increase the milk protein yield (WMD = 0.04 kg/d, [95% CI: 0.00, 0.08]). Regression analysis showed that graded increases of total digestible Arg supply had linear effects on milk yield and milk fat yield. These findings indicated the beneficial effects of supplemental Arg on lactational performance in dairy cows.