Strategies of feeding supplemental soybean meal to primiparous dairy cows
1996
Robinson, P.H.
Primiparous dairy cows were utilized in two experiments to evaluate the productive benefits of modifying the strategy of within-day feeding of soybean meal (SBM) as a supplement to a basal mixed ration fed twice daily. The design of the two experiments was the same, although one was completed with early-lactation cows and the other with late-lactation cows. The evaluation of protein status of all treatments, after the experiments were complete, indicated that cows were limited by supplies of digestible undegraded intake protein (DUIP) on all treatments of both experiments. However, benefits of feeding 800 g d-1 of supplemental SBM versus none were primarily restricted to enhanced production of milk protein, and it is suggested that this was primarily the result 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, respectively, 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 apparently inconsistent production responses between stages of lactation are consistent with a hypothesis that microbial growth is progressively 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-soluble N levels would be lowest (i.e., pre-feeding) would be beneficial for stimulating microbial growth prior to ingestion of the mixed ration.
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