Abstract
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.
Highlights
Our work was conducted as a pilot study to provide information about casein use by dairy cattle and to develop a model for evaluating amino acid use by high-producing dairy cows
The time course data that was used to determine the necessary adaptation periods for responses to abomasal casein infusion are presented for milk urea-N (Figure 1A), N intake (Figure 1B), milk N secretion (Figure 1C), urinary N excretion (Figure 1D), fecal N excretion (Figure 1E), retained N (Figure 1F), productive N (Figure 1G), N efficiency (Figure 1H), total dry matter intake (Figure 2A), milk yield (Figure 2B), milk protein yield (Figure 2C), milk protein content (Figure 2D), milk fat yield (Figure 2E), milk fat content (Figure 2F), milk lactose yield (Figure 2G), and milk lactose content (Figure 2H)
For the 400 g/day casein infusion, urinary N excretion increased over the initial 4 days of the period, whereas retained N and N efficiency decreased over these initial 4 days, with these effects demonstrating the time required for equilibrium to be reached
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. To study amino acid use of lactating dairy cattle, it is necessary to have a model where the cow can respond to amino acid supplementation with increases in milk protein production, body protein deposition, or both. A large number of trials have evaluated methionine and lysine supplementation to lactating cows [1,2], but fewer have evaluated other potentially limiting amino acids [3,4]. The study of amino acid use has been hampered by a lack of models that consistently demonstrate responses to amino acid supplementation, in cows fed typical diets and with typical levels of lactational performance
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