NUTRIENT-REQUIREMENTS FOR DAIRY-CATTLE OF THE NATIONAL-RESEARCH-COUNCIL VERSUS SOME COMMONLY USED RATION SOFTWARE

The first edition of the Nutrient Requirements of Dairy Cattle was pub lished by the National Research Council (NRC) in 1945. The current doc ument is the sixth revised edition, published in 1989, and it ap peals that we are a few years from another edition being in print. Software designed to evaluate and formulate rations for dairy cattle commonly determine nutrient requirements using the NRC as a standard. However, the generation of new knowledge in dairy nutrition occurs more rapidly than the release of the NRC publication, and the developers of the so ftware often modify the requirements based on more recently published research, geographical peculiarities, or factors not explicitly consid ered by NRC. The first step in evaluating or formulating rations is th e prediction of dry matter intake (DMI). The primary variables used by NRC to predict DMI are body weight (BW) and fat-corrected milk (FCM) yield; however, developers of software programs often use different eq uations based on personal preference, availability of research data wi th given equations, and incorporation of other factors in addition to BW and FCM yield. The additional factors are included to provide a mor e dynamic estimation of DMI and, therefore, reduce the difference betw een predicted and actual DMI. Nutrients required for maintenance, lact ation, and growth must be consumed in adequate quantities (e.g., kilog rams or calories), but the dietary concentration of nutrients for a gi ven animal group may differ because of DMI. Even when nutrients are fe d above the requirements, dietary concentrations of nutrients may be i mportant in some situations to minimize the risk of underfeeding cause d by variability in the nutrient composition of feedstuffs and to acco unt for interactions of certain nutrients (e.g., minerals). New resear ch discoveries need to be incorporated into ration formulation strateg ies promptly, and the strategies used for ration formulation need to b e dynamic.