Abstract
SUMMARYForty Holstein dairy cows in their first and second lactations were used from 4 weeksprepartumto 10 weekspostpartumto investigate the effects of feeding ruminally protected methionine and choline on plasma metabolites. Cows were randomly assigned to one of the following treatments in a 2×2 factorial design 4 weeks before their expected calving dates, using randomized blocks based on parity: no supplement (control), 18 g/d of rumen-protected methionine (RPM) product, 60 g/d of rumen-protected choline (RPC) product, or 18 g/d of RPM+60 g/d of RPC. Treatments did not affect plasma triglycerides, glucose, total protein, nonesterified fatty acids (NEFA),β-hydroxybutyrate (BHBA), plasma urea nitrogen (PUN) or aspartate aminotransferase (AST) during theprepartumperiod. Forpostpartumplasma NEFA concentrations, there were interactions between RPC or RPM and weekpostpartum. Feeding RPM increased plasma AST concentrations (P<0·05) and decreased plasma protein concentrations (P<0·05) inpostpartumcows. After calving, feeding RPC increased (P<0·05) dry matter intake (DMI), milk yield, 40 g/kg fat-corrected milk (FCM) yield and energy-corrected milk (ECM) yield. This suggests that supplemental RPC can improve lactation performance of dairy cows.
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