Adjusting Nutrient Requirements of Beef Cattle for Animal and Environmental Variations

Abstract

Requirements determined under standardized conditions are applied indiscriminately to an infinite combination of animal, management and environmental conditions. A model was developed to adjust maintenance requirements for various combinations of temperature, wind, hide, hair coat, activity and previous and present planes of nutrition. Maintenance energy requirements range from values equivalent to National Research Council (NRC) recommendations (no stress) to over four times NRC values under extreme environmental conditions, according to this model. Expanding NRC requirement equations for growing cattle from five categories (three for steers and two for heifers) to 162 categories for each sex class helps minimize the risk of an error in describing the cattle. A model was developed to expand NRC requirements for beef cows from two constant amounts of milk production to six lactation curves; it calculates monthly lactation requirements for nine mature sizes of cows. To aid in allocating forage, a system was presented for determining metabolizable energy requirements for the beef cow-calf unit. Requirements for the cow-calf unit range from equivalent to NRC during early lactation to values 70% higher than NRC estimates near the end of lactation; errors in pasture allocation can reduce weaning weight severely.

© American Society of Animal Science 1988