Effects of Dietary Rumen-Protected Betaine on Lactation Performance and Serum Metabolites of Mid-lactation Holstein Dairy Cows.

This experiment was conducted to investigate the effects of dietary rumen-protected betaine (RPB) supplementation, as partial replacement for methionine, on the lactation performance of mid-lactation dairy cows. A total of 36 Holstein dairy cows were randomly assigned to three groups [control, 20 g/day RPB, or 15 g/day rumen-protected methionine (RPM)]. The experiment was conducted over 9 weeks, with the first week for adaptation. Blood metabolites were analyzed with metabolomics in the control and RPB groups. The results revealed that the milk yield and milk protein content were higher in cows fed RPB and RPM compared to those in the control group. Concentrations of nine metabolites differed between cows in the RPB and control groups. These metabolites were mainly concentrated in six pathways, such as arginine synthesis and proline degradation and cyanoamino acid synthesis. This study revealed that RPB can spare methionine and improve lactation performance of dairy cows fed with diets moderately deficient in methionine.