Breeding & Genetics: Swine, sheep, goat and dog breeding

Economic weights for sow productivity traits in pure-line pig populations were derived from a single profit equation in order to provide flexibility to alternative market requirements or production systems. The profit function method was modified to account for differences in piglet perinatal survival environment imposed by litter size at birth. Both the 100kg finished pig and the feeder pig market were considered. As an example, the economic weights were calculated from average trait values in Ontario purebred Yorkshire herds and provincial average prices and costs. Based on the unmodified profit function, when the mean litter size was increased from 6 to 16 pigs, and all other traits remained constant, the economic weight for total litter size was constant, and those for survival traits increased from $0.16/% to $0.43/% for the finished pig market. When the profit function was modified, the weight for litter size decreased as mean litter size increased, from $2.51/pig for 6 pigs/litter to $1.76/pig for 16 pigs/litter. Economic weights for all other traits were the same as before the modification. The effect was similar for the feeder pig market. Short-term profit in the finished pig market from index selection with economic weights for a mean litter size of 8 pigs was 97% of that based on the correct weights when the mean litter size was 12 pigs, and 87% when the mean litter size was 16 pigs. Profit from selection for litter size alone was 85% of the maximum attainable from selection on the correct index in the finished pig market, and 51% of the maximum in the feeder pig market for an average litter size of 12 pigs. Relative predicted gains from selection on either reduced or incorrect indices decreased with the length of the selection program, and in some cases the decrease became substantial in the long-term.