STRATEGIES OF FEEDING SUPPLEMENTAL SOYBEAN-MEAL TO PRIMIPAROUS DAIRY-COWS

Primiparous dairy cows were utilized in two experiments to evaluate th e productive benefits of modifying the strategy of within-day feeding of soybean meal (SBM) as a supplement to a basal mixed ration fed twic e daily. The design of the two experiments was the same, although one was completed with early-lactation cows and the other with late-lactat ion cows. The evaluation of protein status of all treatments, after th e experiments were complete, indicated that cows were limited by suppl ies of digestible undegraded intake protein (DUIP) on all treatments o f both experiments. However, benefits of feeding 800 g d(-1) of supple mental SBM versus none were primarily restricted to enhanced productio n of milk protein, and it is suggested that this was primarily the res ult of the contribution of DUIP from SBM to intestinal protein supply. Feeding SBM in two versus four daily meals either 1 or 1 and 5 h, res pectively, after offer of the mixed ration had no influence on animal performance at either stage of lactation. However, feeding SBM in two daily meals 1 h prior to the mixed ration versus in two daily meals 1 h after offer of the mixed ration enhanced milk, milk energy, and milk lactose output in late lactation, but not in early lactation. These a pparently inconsistent production responses between stages of lactatio n are consistent with a hypothesis that microbial growth is progressiv ely restricted as supplies of degraded intake protein (DIP), relative to requirements, decline. Under these conditions, which applied to the late-lactation cows, feeding DIP at times of the day when rumen-solub le N levels would be lowest (i.e., pre-feeding) would be beneficial fo r stimulating microbial growth prior to ingestion of the mixed ration.