Predicting individual feed requirements of cattle fed in groups.
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A published model designed to predict individual feed required for the observed shrunk BW and ADG of growing cattle when fed in groups was modified and evaluated to improve its accuracy. This model is needed to accurately bill feed and compute cost of gain in marketing programs based on individual animal management. Because of its importance in predicting energy required for growth, a database of 401 steers was used to develop an equation to predict percentage of empty-body fat (EBF) from carcass measurements (12th rib fat thickness, hot carcass weight, USDA quality grade, and longissimus muscle 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 variation in the carcass measurements at a particular EBF observed in this study indicates further improvement is limited by the inability of carcass measurements to account for variation in fat distribution in the various carcass components. Because of its importance in setting the target end point, a database of 1,355 steers and heifers was used to determine the relationship between EBF and USDA quality grade. These data indicate growing and finishing 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 steers from different breeds from two serial slaughter studies indicated 14.26 +/- 1.52 kg of empty BW change are required to increase EBF one percentage unit for cattle fed high-energy diets; this adjustment is needed to adjust final shrunk BW to the target EBF end point. The model to predict DM required with modifications developed in this study was evaluated with data from 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 applied 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 end point) and can be used to fairly allocate feed to individuals fed in a group under commercial feedlot conditions.
