Effects of rumen-protected methionine and lysine on milk yield and milk composition in Holstein dairy cows consuming a corn grain and canola meal-based diet

Methionine (Met) and lysine (Lys) are thought to be the two most important amino acids for lactation performance. Met and Lys dietary supplementation can thus be an effective approach to improve amino acid balance for lactation performance, particularly in early lactation. The purpose of this study was to determine how rumen-protected (RP) Met + Lys affect milk production, milk composition, and feed efficiency in primiparous Holstein dairy cows fed a corn grain and canola meal-based diet for 60 days (8.5 weeks) following calving. Two hundred primiparous Holstein dairy cows were randomly assigned to one of two dietary treatments based on their expected calving date: 1) a basal diet; or 2) a basal diet supplemented with RP Met + Lys. Milk production and feed consumption were tracked on a daily basis, and milk components were tested once a week. During the trial, drinking water was always available in front of the dairy cows. The RP Met + Lys considerably increased (p 0.05) milk yield (+ 2.20 kg/d), fat corrected milk yield (+ 2.18 kg/d) and feed efficiency but had no effect on dry matter intake (p 0.05) the proportion of milk fat, but had no effect on the other milk composition markers (p 0.05). Except for milk crude protein, the yields of fat, true protein, lactose, and energy in milk were higher (p < 0.05) in cows fed RP Met + Lys vs. control cows. The results indicate that supplementing with RP Met + Lys after the first calving has a considerable impact on subsequent milk and milk fat production, as well as the yield of the majority of milk nutrients.