Case Study: Effect of strategic ration balancing on the efficiency of milk protein production and environmental impact of dairy cows in a commercial herd

Three experiments were conducted with the objective of evaluation of supplementing rumen-protected Lys, rumen-protected Met, and RUP on productive performance, dietary N utilization, ammonia emission, and economic profitability. In Exp. 1 and 2, multiparous cows were fed (1) a control diet that represented the current herd diet (~17.5% CP) or (2) a reformulated diet (15.9−17.6% CP) supplemented with rumen-protected Lys, rumen-protected Met, and RUP. In Exp. 3, primiparous cows were fed (1) a control diet that represented the current herd diet (17.7% CP) or (2) a reformulated diet (16.7% CP) supplemented with rumen-protected Lys, rumen-protected Met, and RUP. The DMI was numerically similar between control and reformulated diets. Compared with the control diets, the yields of milk, milk protein, lactose, and solids nonfat were greater for the reformulated diet in Exp. 1, less in Exp. 2, and similar in Exp. 3. The yield of milk fat was greater for the reformulated diet in Exp. 1 and similar in Exp. 2 and 3. When the cows were fed the reformulated diet, the excreted manure N was numerically reduced by 4.8% to 14.7%, and milk N efficiency was increased by 6% to 10.3%. The ammonia emission from manure in cows fed the reformulated diet was numerically less in Exp. 1 and 2 and similar with control in Exp. 3. When cows were fed the reformulated diets, the income over feed cost was consistently greater than control only in Exp. 3. In conclusion, cows fed lower CP diets at a commercial farm could maintain milk production, improve the milk N efficiency, and reduce the manure N excretion and ammonia emission when the diets were reformulated and supplemented with rumen-protected Lys, rumen-protected Met, and RUP.