SELECTION FOR CARCASS AND FEEDLOT TRAITS CONSIDERING ALTERNATIVE SLAUGHTER END-POINTS AND OPTIMIZED MANAGEMENT

Profit was defined as a function of the genotype of animals and variab les controlled by management. Alternative parameterizations of managem ent variables were examined to compare the effect of controlling age a t slaughter, weight at slaughter, or fat depth at slaughter. The vario us parameterizations are shown to result in equivalent economic weight s for genetic variables, provided management variables are optimized f or the current genotype. The implication is that economic weights and selection indexes can be conveniently calculated for age constant end points even though commercial production may involve weight or backfat depth constant slaughter points. An example of selection for profit i n the feedlot phase of beef production is presented. Three genotype-ma nagement combinations were considered. Economic weights and subsequent selection index weights were shown to depend on both average genotypi c means and management (feeding and marketing program) factors.