Impact of Dietary Protein Amount and Rumen Undegradability on Intake, Peripartum Liver Triglyceride, Plasma Metabolites, and Milk Production in Transition Dairy Cattle

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Abstract
Feeding strategies of transition dairy cows contribute to the risk factors associated with metabolic disorders that limit production in the ensuing lactation. To investigate the effects of prepartum dietary crude protein (CP) concentration and amount of rumen-undegradable protein (RUP) on postpartum health and production, 44 multiparous Holstein cows were blocked by expected calving date and assigned to one of four isoenergetic prepartum rations beginning 28 d prior to expected calving date. Prepartum rations were: 12% CP and 26% RUP, 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry matter basis. All cows were fed the same postpartum diet (18% CP, 40% RUP) from 1 to 56 d in milk (DIM). Prepartum dry matter intake (DMI) was not different among dietary treatments. Mean postpartum intakes (kg/d) were higher through 56 DIM (P<0.05) for cows fed the 12% CP:26% RUP diet prepartum compared with any of the 16% CP diets (21.8 vs. 19.8, 18.6 and 18.6; 12% CP:26% RUP vs. 16% CP:26% RUP, 16% CP:33% RUP and 16% CP:40% RUP). There was a DIM x prepartum diet interaction (P<0.05) with the greatest effect of the 12% CP:26% RUP diet evident during the first 35 DIM. Cows fed the 12% CP:26% diet during the transition period tended to produce more milk (kg/d) (P = 0.08) than did cows fed any of the 16% CP diets (40.8 versus 37.8, 38.7, and 37.4; 12% CP:26% RUP vs. 16% CP:26% RUP, 16% CP:33% RUP, and 16% CP:40% RUP). Additional protein (12 vs. 16% CP) in the prepartum diet tended to decrease milk protein (P = 0.10) and milk fat yield (P = 0.08) but did not alter percent milk fat, percent milk protein, or MUN. Liver triglyceride (TG) expressed as milligrams of TG per microgram of DNA or percentage of dry matter (DM) on d -28, -14, +1, +28, and +56 relative to calving were not significantly different among treatments. Maximal (P<0.05) infiltration of TG in liver was observed on +1 d when expressed as a percentage of DM and on +28 d when expressed as milligrams of TG per microgram of DNA. Plasma glucose, calcium, urea nitrogen, beta-hydroxybutyrate, and nonesterified fatty acids were not different (P<0.05) among treatments. The data indicate carryover effects of prepartum dietary protein on postpartum intake and milk production, pointing to beneficial effects of maintaining dietary protein for dairy cows in late gestation at 12% CP.