Ten generations of selection for predicted weight of testes in swine: direct response and correlated response in body weight, backfat, age at puberty, and ovulation rate.

Selection for predicted weight of testes at 150 d of age (PWT) was practiced for 10 generations to determine the effect on reproductive and growth traits in swine. Mass selection among boars (line TS) or random selection (line C) was practiced beginning with the F3 generation of a Large White x Landrace composite population. Population size in each line was 40 to 45 litters by 15 sires per generation. Responses were estimated by regressions on cumulative selection differentials for PWT and on generation number and by mixed-model derivative-free REML procedures. The realized heritability of PWT was .35 +/- .02 and the response per generation was 19 g (P < .01). Correlated responses in body weight were .95 +/- .37 (140 d) and 1.13 +/- .42 kg (160 d) per generation for boars and .70 +/- .32 (130 d) and .64 +/- .46 kg (180 d) per generation for gilts. Response in backfat was .08 +/- .14 mm per generation in boars and .16 +/- .14 mm in gilts. Negative genetic trends occurred in age at puberty in both lines, but the difference between lines was not significant. At Generation 10, ovulation rate was .76 +/- .43 eggs more for gilts of the TS line than for C gilts. Genetic correlations of PWT with other traits are presented. Heritability of PWT was moderately high and its phenotypic variance was large; therefore, a high rate of response of 5.5% per generation occurred. Selection for PWT was not effective in decreasing age at puberty or increasing ovulation rate of daughters.