Swine Selection Indexes including Live Animal Measurements as Indicators of Carcass Merit

Estimates of heritability were obtained by doubling the intra-sire daughter-dam regression. These estimates were 0.20 and 0.40 for number of pigs in a litter at 154 days and individual pig weight at 154 days, respectively. The genetic correlation between these traits was estimated to be 0.24. Theoretical aspects of the biases of these estimates when maternal environment is involved are presented. The method of Hazel, as modified by Henderson, for constructing a selection index was compared to a prediction of a single estimate of progeny “economic value” from the dam's phenotype. The relative economic values of a unit change in individual pig weight at 154 days of age, percent lean cuts, and litter size at 154 days, in terms of net income, were estimated at 1:2.67:20, respectively. The estimate of the correlation of the index on the dam with the index on her progeny by the former method is 0.16 whereas the comparable correlation of information on the dam with “economic value” on her progeny is 0.22. Comparison of the two methods by these correlations indicates that they lead to essentially the same results. The latter method appears to be more practical since it is easier to calculate and data suitable for calculation of the index are more readily available. Also, it predicts the overall merit of the offspring rather than requiring separate estimates of the components, each with its own error. The index proposed for practical use appears not to be quite as accurate as others calculated in this study but has the advantage of containing fewer variables and requiring that potential breeding stock only (boars and gilts available for selection) be measured. The proposed index is: I′d=164+.5 X1X-4 X4−43.3 X6 + 1.2 X7−2 X8. It is based on individual weight (X1, lb.), length of foreleg (X4, cm.), backfat at the loin (X6, in.), number in litter at farrowing (X7) and number in litter at 154 days (X8).