CASE STUDY: Application and evaluation of the Cornell Net Carbohydrate and Protein System as a tool to improve nitrogen utilization in commercial dairy herds

Nitrogen utilization is becoming a central component in ration balancing as dairy producers try to maximize milk protein yields, decrease feed costs, and conform to current environmental standards. Feeding excess CP can result in unnecessary feeding expenses with no return in milk income in addition to having important negative environmental consequences. Recent changes to the Cornell Net Carbohydrate and Protein System (CNCPS) have resulted in increased model sensitivity to N intake and requirements allowing rations to be developed with reduced environmental impact. Farm level studies are required to evaluate the applicability of the updated model on commercial farms. In this study, the CNCPS (v6.1) was used to adjust the diets of 2 commercial herds in western New York to improve N utilization and reduce feed costs while maintaining high levels of milk production (part 1). In addition, 13 herds that were producing high levels of milk (39.3 ± 5.1 kg/d per cow; mean ± SD) on low CP diets (14.3 to 16.5% DM) were characterized as examples of attainable N utilization targets (part 2). In part 1, CP was reduced by approximately 1% DM, milk urea N was decreased by approximately 2 mg/dL, and income over feed cost was improved on both farms. Part 2 indicated that high milk and milk protein yields can be achieved on diets supplying less than 16% CP and that N use efficiency can be as high as 38%. This study confirms that the updated CNCPS can be successfully used to develop diets that enhance N use efficiency under the constraints of a modern commercial dairy farm.