A method for improving efficiencies in livestock production comprises grouping livestock animals, such as cattle and pigs, during the period of their retention in a feeding facility according to the genetic predisposition of individual livestock animals to deposit fat, and then feeding the animals in each group substantially uniformly. Such genetic predisposition is determined by determining homozygosity or heterozygosity of each animal with respect to alleles of a gene encoding an adipocyte-specific polypeptide, termed leptin, which gene is hereinafter referred to as ob, segregating such animals into groups based on genotype and optionally phenotype, feeding and otherwise maintaining animals in a group together and apart from other groups of animals, and ceasing to feed the animals in the group at a time when the median body fat condition of the animals of that group is a desired body fat condition. Packers can also more accurately predict the fat deposition in carcasses of live animals it purchases, leading to increased efficiencies.