Predicting individual feed requirements of cattle fed in groups

A published model designed to predict individual feed required for the obse rved shrunk BW and ADG of growing cattle when fed in groups was modified an d evaluated to improve its accuracy. This model is needed to accurately bil l feed and compute cost of gain in marketing programs based on individual a nimal management. Because of its importance in predicting energy required f or growth, a database of 401 steers was used to develop an equation to pred ict percentage of empty-body fat (EBF) from carcass measurements (12th rib fat thickness, hot carcass weight, USDA quality grade, and longissimus musc le area), which accounted for 61% of the variation in EBF with no bias (P > 0.1). When tested with an independent data set of 951 steers, the equation accounted for 51% of the variation with 1% proportional bias. The large va riation in the carcass measurements at a particular EBF observed in this st udy indicates further improvement is limited by the inability of carcass me asurements to account for variation in fat distribution in the various carc ass components. Because of its importance in setting the target end point, a database of 1,355 steers and heifers was used to determine the relationsh ip between EBF and USDA quality grade. These data indicate growing and fini shing cattle reach Select and low-Choice quality grades at an EBF of 26.15 +/- 0.19 and 28.61 +/- 0.20%, respectively (P < 0.05). A data set of 228 st eers from different breeds from two serial slaughter studies indicated 14.2 6 +/- 1.52 kg of empty BW change are required to increase EBF one percentag e unit for cattle fed high-energy diets; this adjustment is needed to adjus t final shrunk BW to the target EBF end point. The model to predict DM requ ired with modifications developed in this study was evaluated with data fro m 365 individually fed cattle and it accounted for 74% of the variation in observed DM consumed with no bias (P > 0.1). When the revised model was app lied to a commercial feedlot data set containing 12,105 steers and heifers, the total observed DM consumed was predicted with a bias of less than 1%. The model presented in this study accounts for differences known to affect animal requirements (breed type, BW and ADG, and weight at the target EBF e nd point) and can be used to fairly allocate feed to individuals fed in a g roup under commercial feedlot conditions.