SYSTEM OF EQUATIONS FOR FULFILLING NET ENERGY AND ABSORBED PROTEIN-REQUIREMENTS FOR MILK COMPONENT PRODUCTION

Objectives were to develop a system of equations for formulating ratio ns to meet absorbed protein requirements, to define NE(L) requirements for individual milk components, and to evaluate the effects of change s in milk composition on requirements for absorbed protein and NE(L) r ecommended by NRC or by a proposed system based on milk components. By combining parameters in the NRC degradable protein system, a set of t wo equations was derived that can be solved to meet absorbed protein r equirements when either ruminally available protein or energy limits m icrobial protein synthesis. Heats of combustion were used to estimate NE(L) requirements for milk components. Maintenance requirements for a bsorbed protein and NE(L) were obtained from NRC. To eliminate the dep endence of DMI prediction on milk fat concentration, as assumed by NRC , DMI was estimated using the NDF concentration of the feed and the NE (L) requirement of the cow. The proposed system of requirements, based on milk components and the matrix of equations for meeting absorbed p rotein requirements, not only accounts for differences in the degradab ility and microbial yield of feeds but also more logically matches dif ferences in nutrient requirements for milk components associated with changes in milk composition.