Impact of dietary rumen undegradable protein and rumen-protected choline on intake, peripartum liver triacylglyceride, plasma metabolites and milk production in transition dairy cows.

The objectives of the present study were to determine the effects of rumen undegradable protein (RUP) level of prepartum diets, the supplementation of a rumen-protected choline product, and their interactions on milk production, feed intake, body weight and condition, blood metabolites, and liver triacylglycerides in dairy cows. Rumen-protected choline (RPC) was fed with two levels of RUP to 48 multiparous Holstein cows in a 3 x 2 factorial arrangement of treatments. Beginning 28 d before expected calving, cows were fed 10% rumen degradable protein, either 0, 6, or 12 g/d of RPC as CapShure (Balchem Corp., Slate Hill, NY) and either 4.0 or 6.2% RUP. After calving and through 120 d of lactation, cows received a common diet and continued RPC as per their prepartum assignment. Prepartum dry matter intake (kg/d) was not affected by RPC or RUP. Postpartum intake decreased when 6.2% RUP was fed prepartum. Milk production to 56 d in milk was decreased when cows were fed 6.2% RUP prepartum. Milk protein (kg/d) decreased when additional RUP was fed prepartum. Cows fed RPC lost more weight during the study period and tended to lose more body condition. Plasma urea nitrogen levels in the prepartum period were reduced for cows fed 4.0% RUP prepartum. Mean liver triacylglyceride determined from samples obtained at -28, -14, +1, +28, and +56 d in milk was not affected by RPC, prepartum RUP, or their combinations. Feeding 12 g of RPC/d in conjunction with 4.0% RUP increased milk production, but feeding RPC with 6.2% RUP prepartum and through 56 d in milk decreased production. The data indicate that 6.2% RUP does not benefit close-up dry cows, and the response to RPC depends the RUP content of the prepartum diet.