Influence of ingredient reformulation to reduce diet crude protein level on productivity, and efficiency of dietary nitrogen use, in early lactation dairy cows

Holstein dairy cows were used to determine responses to reduction in the crude protein (CP) concentration of the diet fed during the immediate postpartum period due to removal of some buffer soluble CP, as well as prepartum and postpartum supplementation of ruminally protected Lys and Met, on productivity and gross efficiency of N utilization (i.e., milk N/feed N) during early lactation. Cows in both groups were fed a totally mixed ration (TMR) containing timothy silage and a grain based concentrate during the prepartum period, either with or without supplemental ruminally protected Lys and Met. At calving, cows were fed one of the two TMR containing timothy silage, corn silage, and one of two grain based concentrates, with or without supplemental ruminally protected Lys and Met, for 42 days. There was no difference in productive performance of the two groups of cows during lactation, although there were numerical increases in milk, milk protein, and milk lactose production, as well as a numerical decline in milk fat production, for the CP reduced group that led to an essentially identical energy balance between the two groups. The gross efficiency of N utilization was higher (P<0.05) in the CP reduced group. It is possible to maintain productivity of dairy cows in early lactation with buffer soluble CP reduced rations, and increase the proportion of N captured in milk protein, by precision ration formulation based upon nutrients, without changing feedstuffs in the ration.