Selection indices for Canadian beef production using specialized sire and dam lines

Abstract

Relative economic values and literature estimates of genetic and phenotypic variances and covariances were used to develop selection indices for specialized maternal and terminal strains of beef cattle. The envisioned commercial production setting used three maternal strains mated in rotation. Yearling heifers were mated to a terminal sire strain (M3) to minimize dystocia and neonatal mortality without closely monitored calving. Mature cows were bred to a second terminal strain (TX) to produce market progeny. Acccuracies for all indices were low: 0.22, 0.22 and 0.19 for the maternal strains, M3 and TX, respectively. Predicted correlated responses to index selection were not economically favorable for all traits within strain but were offsetting between strains. At the production system level, genetic improvement in profitability resulted from all traits except feed conversion. Fertility and calf survival were improved in all strains. Direct genetic potential for growth was reduced in the maternal strains but was increased in TX and to a lesser degree in M3. There was a tradeoff between maternal and terminal strains in responses of carcass traits. Maternal strains increased in dressing percentage and decreased in cutability, while M3 and TX decreased in dressing percentage and increased in cutability. Arduously slow improvement in profitability is anticipated: $1.07 per breeding female per unit of selection response. Key words: Beef cattle, selection program, selection index