Meeting the protein requirements of dairy cows is achieved by providing adequate amounts of amino acids in the appropriate ratios to maintain health and productivity throughout lactation. Methionine is an essential amino acid that has additional physiological functions beyond its role in milk protein synthesis. Supplementation of rumen-protected Met (sRPMet) in stable lactation results in increased milk protein production and a consistent increase in milk fat. Feeding sRPMet to dairy cows before and after calving has been evaluated in several trials, which are summarized in this meta-analysis.
The studies provided sRPMet both before delivery (mean 8.20 [±2.94] g metabolizable sRPMet/d, starting at 19.3 [±4.23] days before parturition) and after delivery (10.53 [±3.30] g metabolizable sRPMet/d for a mean of 85.9 [±38] days of lactation).
Prepartum DMI and pre- and postpartum BW and BCS were not affected by sRPMet. In contrast, postpartum DMI, milk yield, milk fat and true protein yield, and milk fat and true protein concentration were increased by sRPMet. Most production responses to sRPMet decreased as lactation progressed, with predicted responses in milk fat and true protein yield being 118 and 92 g/day, respectively, at 21 days of lactation. Postpartum circulating metabolites were not affected by sRPMet; however, the sample size for this analysis was much smaller than for production responses. This meta-analysis suggests that feeding sRPMet pre- and postpartum resulted in increased productivity beyond that achieved by providing sRPMet alone in lactation.
