Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/24/2008
Publication Date: 12/1/2008
Citation: Lanzas, C., Broderick, G.A., Fox, D.G. 2008. Improved Feed Protein Fractional Schemes for Formulating Rations With the Cornell Net Carbohydrate and Protein System. Journal of Dairy Science. 91:4881-4891. Interpretive Summary: Dairy and beef cattle obtain their useful protein (protein that is absorbed by the animal in the form of amino acids and used to make protein) from two sources: protein produced by microbes living in the rumen (the first compartment of the cow’s stomach), and feed protein that escapes breakdown in the rumen and is digested directly by the cow in the small intestine. Feeding too little protein depresses production and, thus, farmer profits diminish; this is also unhealthy for the cattle. Feeding too much protein results in excessive nitrogen excretion, especially in the urine, the form of excretory nitrogen that is most polluting. To mitigate negative environmental effects, it is important that dairy and beef cattle diets be formulated to meet, but not exceed, the crude protein required to provide the cow with useful protein. The nutritional models used by farmers to formulate diets for their animals are intended to accomplish these goals. One such model that is applied around the world for feeding both dairy and beef cattle is the Cornell Net Carbohydrate Protein System (CNCPS). Although an improvement over older feed formulation systems, the CNCPS still is inaccurate in its predictions of how several of the nitrogen fractions behave in the rumen. The objectives of this study were to evaluate several simplified CNCPS protein fractionation schemes to see if any of these modifications improved the system’s accuracy. Two modifications substantially improved how well the CNCPS worked. Compared to the original CNCPS, both modified systems better predicted protein metabolism (protein degradation and escape) in the rumen plus were more accurate at identifying diets that had too little, or too much, crude protein. The CNCPS is used by thousands of farmers and feed consultants throughout the world. Implementation of the modified versions would have the twin benefits of reducing farmers’ feed and feed analysis costs plus reducing nitrogen losses to the environment from dairy and beef production.
Technical Abstract: Adequate predictions of rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) supplies are necessary to optimize performance while minimizing losses of excess nitrogen (N). The objectives of this study were to evaluate the original Cornell Net Carbohydrate Protein System (CNCPS) protein fractionation scheme and to develop and evaluate alternatives designed to improve its adequacy in predicting RDP and RUP. The CNCPS version 5 fractionates CP into five fractions based on solubility in protein precipitant agents, buffers, and detergent solutions. The first fraction A represents the soluble non-protein N; B1 is the soluble true protein; B2 represents protein with intermediate rates of degradation; B3 is the CP insoluble in neutral detergent solution, but soluble in acid detergent solution; and C is the unavailable N. Model predictions were evaluated with studies that measured N flow data at the omasum. The N fractionation scheme in version 5 of the CNCPS explained 78% of the variation in RDP with a root mean square prediction error (RMSPE) of 275 g/d, and 51% of the RUP variation with RMSPE of 248 g/d. Neutral detergent insoluble CP (NDICP) flows were overpredicted with a mean bias of 128 g/d (40% of the observed mean). The greatest improvements in the accuracy of RDP and RUP predictions were obtained with the following two alternative schemes: Alternative 1 used the inhibitory in vitro (IIV) system to measure the fractional rate of degradation for the insoluble protein (B2) fraction in which A = nonprotein N (NPN), B1 = true soluble protein, B2 = insoluble protein, C = unavailable protein (RDP: R2= 0.84 and RMSPE= 167 g/d; RUP: R2 = 0.61 and RMSPE= 209 g/d). Alternative 2 redefined A and B1 fractions as the non-amino-N and amino-N in the soluble fraction, respectively, (RDP: R2 = 0.79 with RMSPE= 195 g/d and RUP: R2 = 0.54 with RMSPE= 225 g/d). We concluded that implementing either alternatives 1 or 2 will improve the accuracy of predicting RDP and RUP within the CNCPS framework.