Amino acid research infusion studies in dairy cows to improve estimates of protein efficiency

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The efficiency with which the typical dairy cow in Canada incorporates dietary amino acids into milk protein could be 50% higher than it is today. Formulating diets for lactating cows so that less N is excreted into the environment requires an accurate prediction of the milk protein response to a change in nutrient intake. Based on new research in growing animals, we hypothesize that milk protein synthesis is regulated by signalling proteins that affect the activity of translational enzymes in the mammary glands of cows. Our objectives are 1) to test the above signalling hypotheses by administering amino acid imbalances and deficiencies to cows, with and without glucose; 2) to quantify the partial efficiencies of amino acid transfer to milk protein under conditions of varying amino acid and glucose supply; and 3) to test the accuracy of predicting milk protein yield using a fixed efficiency of transfer of each essential amino acid into milk compared to variable partial efficiencies. Objectives 1 and 2 will be met with a series of abomasal infusion experiments on lactating dairy cows designed to first identify which amino acids have the largest effect on milk protein yield, and then study those particular amino acids in terms of dose and glucose response. Equations to predict efficiency of amino acid capture in milk will be developed and incorporated into the Newton computer model used by the industrial partner to formulate rations for approximately 30% of the 1.4 million dairy cows in Canada. Objective 3 will be met with a cow feeding experiment where 2 different diets will be fed to cows and observed milk and protein yields will be compared with those predicted by constant and variable efficiency models. Two postdoctoral fellows, 1 graduate student, and 2 undergraduate students will be employed on the project. The findings will be used by the industrial partner to update an operational dairy feed formulation program and to facilitate improvements in protein efficiency on Canadian dairy farms. More efficient utilization of dietary protein by cows would lead to increased profitability of the dairy enterprise, and reductions in agricultural release of nitrogen into the environment.