Effects of fat and rumen-protected methionine supplementation on production response of first-lactation cows

Abstract

To determine whether supplementation of rumen-protected methionine (RPM) and fat, from 0 to 150 days in milk, improves milk production, milk quality, and energy balance (EB), in a completely randomized design, 32 first-lactation cows fed diets with 0 or 3.5% added fat and 0 or 0.15% added RPM. Fat, RPM, and fat plus RPM increased milk yield. Supplemental RPM increased milk protein (%) and decreased milk fat (%). Fat, RPM, and fat plus RPM increased (kg) milk fat, milk protein, and milk lactose. Cows fed fat and RPM alone had greater negative EB values than cows non-supplemented. Cows fed fat plus RPM had similar EB to cows non-supplemented. Supplemental RPM induced higher plasma glucose and lower urea-N. Fat induced higher plasma cholesterol. In conclusion, supplemental fat or RPM, and fat plus RPM increased milk production, but fat plus RPM enhanced EB as compared to fat or RPM alone.