Özet:

: Adequate supply of amino acids can improve the efficiency of nitrogen use. Casein is the predominant milk protein, and its supplementation can improve milk protein synthesis and nitrogen efficiency. We evaluated the effects of post-ruminal supplementation of casein on milk yield and composition and whole-body protein deposition. Two ruminally cannulated Holstein dairy cows (599 kg) were used in a switch-back design, and treatments were an abomasal infusion of 0 or 400 g/day casein. Cows were fed a diet consisting of corn silage, alfalfa hay, wet corn gluten feed, whole cottonseed, and grain mix, and they received 320 g/day dextrose via abomasal infusion to increase energy:metabolizable protein. The experiment used three 8-day periods. Milk, urine, and feces samples were collected to evaluate milk production, milk composition, and nitrogen retention. Abomasal casein infusion increased ( p < 0.01) milk protein percentage and milk urea nitrogen. Nitrogen retention ( p = 0.03) and urinary N excretion ( p < 0.001) were increased and fecal N excretion ( p < 0.001) was decreased by casein infusion. Results suggest casein stimulated protein deposition and altered nitrogen use in lactating dairy cattle. Adaptation periods of 4 days were appropriate for evaluating responses to casein supplementation. Our data provide elements that can aid the design of future experiments.

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