Invited Review: Modifications to the Cornell Net Carbohydrate and Protein System related to environmental issues-Capability to evaluate nitrogen and phosphorus excretion and enteric carbon dioxide and methane emissions at the animal level

The Cornell Net Carbohydrate and Protein System (CNCPS) was developed to predict nutrient supply and requirements in cattle under most management conditions. The ability to develop or integrate extant equations to predict excretion of nitrogen (N) and phosphorous (P) in urine and feces and enteric carbon dioxide and methane is possible because those variables are outcomes of predicting nutrient supply and evaluating requirements. The CNCPS was used to formulate diets in 8 herds in New York, and the application of the model was shown to reduce manure N excretion by 14% and increase income over purchased feed costs per cow by $157 (Chase, 2018). The CNCPS has been used by nutritionists and nutrient management planners to evaluate and predict nutrient excretion and develop management plans for dairy herds over a yearly cycle. Further, the production of carbon dioxide and methane from cattle has been extensively studied as part of the development of DE, ME, and NE equations; thus, if the model is adequate at predicting energy supply and balance, predictions of those gases should be possible to implement because gaseous emissions are accounted for in energy predictions. Equations from Casper and Mertens (2010) for carbon dioxide and Mills et al. (2003) for methane were tested within the CNCPS and demonstrated good accuracy and precision at predicting enteric carbon dioxide and methane emissions (Van Amburgh et al., 2015). The CNCPS can be used to assess the environmental impact of dairy cattle and by nutritionists to improve the utilization efficiency of diets and cattle in the environmental context.