Inbreeding effects on the parameters of the growth function in three strains of Iberian pigs

The growth performance of inbred pigs coming from full-sib matings was compared to that of contemporary animals coming from the same sires mated to control dams. The animals belong to three strains of Iberian pigs with different histories of previous inbreeding. The data consisted of 1,615 weight records between 50 and 250 d of age from 229 pigs. The statistical model assumed the two parameters that describe the linear growth function (a = intercept, b = slope) as different traits (weight at 120 d and daily gain) and the analysis was carried out in a Bayesian framework via Gibbs sampling. The means of the posterior distribution of heritabilities, common litter environmental coefficients, and genetic correlation were 0.328 (h(2)a), 0.332 (h2b), 0.084 (c(2)a), 0.060 (c(2)b) and 0.973 (rhoG). Inbreeding depression, expressed as the performance decrease relative to the mean, per 10% increase of the inbreeding coefficient, was -3.18, -2.31 and -5.37% for weight at 120 d (a), and -3.16, -2.08 and -6.49% for daily gain (b) in each of the three strains. The results indicate that the inbreeding effects are dependent on the level of previous inbreeding, the more previous inbreeding, the less inbreeding depression.