GENETIC-ANALYSIS OF MATERNAL ABILITY IN IBERIAN PIGS

A practical measure of milk yield of the sow is the weight of the litt er at three weeks of age when the piglet growth is entirely dependent on the milking ability of the dam. Genetic parameters of litter size a t birth (LS) and litter weight at 21 days (LW21) were estimated using a DFREML procedure from records of 4883 litters (2,049 for LW21) of Ib erian breed. Preliminary analysis showed negligible maternal genetic e ffects. The model for both traits included the fixed effects of farrow ing per od (86 levels), parity (6) and inbreeding coefficients of dam (Fd) and litter (F1) as co-variables, and three random effects-additiv e genetic value, permanent environmental effect and residual on both t raits. Heritability and repeatability estimates were 0.064 and 0.126 ( LS) and 0.163 and 0.270 (LW21) respectively. Estimated genetic and phe notypic correlations were 0.214 and 0.043. The inbreeding depression p er 10% increase of Fd or F1 was -0.150 or -0.170 in live piglets and - 0.983 or -1.023 kg of litter weight. When the model for LW21 included the dam inbreeding and the number of suckling piglets as co-variables, the heritability and repeatability estimates were 0.243 and 0.431 res pectively. A complementary analysis was carried out on individual reco rds (weight at 21 days) of 26206 piglets farrowed by 1317 sows. The mo de included the fixed effects of sex, farrowing period, parity, and th e inbreeding coefficients of dam and individual, as co-variables. A to tal of four random effects were also included: direct and maternal gen etic effects, common environmental effects and residual. Estimates of heritability, maternal heritability and common environmental coefficie nt were, respectively, 0.019, 0.163 and 0.128, reinforcing the evidenc e of genetic variance for milk producing ability in Iberian sows. The estimated values of inbreeding depression for piglet weight at 21 days were -0.072 and -0.098 kg per 10% increase in dam or litter inbreedin g.