Litter Productivity in Large White Pigs: 2. Heritability and repeatability estimates

Abstract

Estimates of the heritability, the repeatability and the genetic correlation coefficients of litter performance traits were calculated from data on 38 000 Large White litters farrowed in 146 British herds. The repeatability estimates of number of live pigs per litter at birth, three weeks and eight weeks were 0-15, 0-14 and 0-14 respectively. The corresponding heritability estimates were 0-07+0-02, 0-07+0-02 and 0-09+0-03, respectively. The repeatability estimates of litter weight at three weeks and eight weeks were 0-15 and 0-04, while the corresponding heritability estimates were 0-08+0-02 and 0-03+0-02. High positive genetic and phenotypic correlations were obtained between litter size and litter weight. A number of model culling schemes were considered and it was found that even at relatively high culling levels the improvement in overall herd mean performance was very small. Direct selection for litter size may yield a useful rate of improvement if selection is confined to one trait and large selection differentials are achieved, but could not be economically justified.

Studies on a Two Trait Selection Experiment in Pigs

“…His estimate of heritability for average pig weight at 21 days was 0.35, while his repeatability estimates were lower than those of Table 8. Strang &King (1970) found repeatabilities similar to Eikje (1970). Piglet weights at 3 and 8 weeks showed much lower values from that study compared with the Norwegian data.…”

Genetic relationships of reproduction with growth and with carcass traits in British pigs

“…Although litter sizes and litter weights are highly correlated at the phenotypic and genetic level (Strang and King, 1970), they express different aspects of fitness, for example ovulation rate, piglet survivability and early growth rate (Smith and King, 1964). However, it appears from Table 4 that the signs of the genetic correlations are consistent across litter productivity traits for each of the biological measures of growth and carcass except 'eyemuscle' area (EMA).…”

“…Combining information for (a) heritabilities of reproductive traits from Strang and King (1970), (b) recent heritability estimates for growth and carcass traits from MLC (G. L. Cook, personal communication), and (c) mean sizes of progeny groups and sib groups from the present data, the accuracy of estimates on individuals was calculated for reproductive traits and for growth and carcass traits.…”

“…The average parity declined from the first to the last year of data studied, giving a mean reproductive performance for each parity group whose estimate was confounded with time (or season) effects. In addition, using herd and parity corrections, Strang and King (1970) reported that repeatability estimates were small (about 15 %). Therefore data on reproductive performance for animals recorded at different parities were not combined in this study.…”

“…Smith's (1964) terminology is used in the following discussion. The ratio, p, of the heritability for reproductive performance and for the index of growth and carcass merit is taken as 0-20 (using heritability values from Strang and King (1970) for gilt litter size of 0-10, and for the index of 0-51 (D. E. Steane, personal communication)). The relative economic value, a, is given by the ratio of economic values for reproduction, a v and for the index, 02.…”