Varying Protein Content and Nitrogen Solubility for Pluriparous, Lactating Holstein Cows: Lactation Performance and Profitability

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Abstract
Effects on total lactation performance of varying ration crude protein (15.3 vs. 13.6% of dry matter) and nitrogen solubility (35 vs. 45% of total nitrogen) in early lactation was studied using 57 pluriparous Holstein cows. Grain was fed according to production so as to minimize change in body wt throughout lactation. Forages high in nitrogen solubility, corn and grass silages, were fed free-choice. Percent concentrate in ration dry matter was highest (64%) 5-8 wk postpartum and lowest (35) 33-44 wk postpartum. Protein and nitrogen solubility were varied by formulating 4 protein supplements fed as 10% of the grain allocation, so differences in treamtents applied narrowed as lactation progressed. Cows fed the medium-protein diets produced 196 kg more milk than those receiving low-protein diets, but their peak daily milk yield was only 0.6 kg higher. Cows receiving rations with reduced nitrogen solubility produced 347 kg more milk than those fed the higher solubility diets, but their peak daily milk yield was 1.0 kg lower. Income above fed cost for the lactation was highest and postpartum loss in body wt was least for cows receving medium-protein and low solublity rations in early lactation, but not differences were significant. Both milk yield (38.3 to 40.6 kg) and total dry matter intake (3.74 to 3.91% body wt) means were maximum 6-7 wk postpartum, but lactation performance was not proportional to peak milk yield. When cows are fed to minimized body fat mobilization, response to increased protein in the diet is small. Reducing nitrogen solubility of silage-based diets increased milk produced per unit grain fed. There were no adverse effects of treatments on breeding efficiency or herd health.