Genetic and environmental factors affecting reproductive traits in sows in an outdoor production system

The aim of this study was to characterize the genetic (crossbreeding and additive genetic) and environmental factors affecting reproduction of sows on an outdoor production system. Data from the Experimental Swine Unit of Facultad de Agronomía, Progreso, Uruguay, were used. The breeding herd included purebred Pampa Rocha (P) and Duroc (D), as well as hybrid (H: P×D and D×P) sows. Pampa Rocha is considered the only local swine breed of Uruguay. The dataset contained 1309 litter records from 197 sows (136 P, 22 D and 39 H) collected from 1997 to 2011. Feeding was based on grazing, restricting the use of concentrate to the breeding herd. The variables analysed were: number of piglets born alive (PBA), average piglet weight of the litter at birth (ABW), number of piglets weaned (PW), average piglet weight of the litter at weaning (AWW), survival from birth to weaning (S) and weaning-to-conception interval (WCI). The following fixed factors were included in the final model: year of farrowing, time of the year (month or season, depending on the variable analysed), inbreeding of the sow, parity number, weaning age, direct breed effects, individual heterosis, repeated measures on the sow (used to estimate the permanent environment effect), and the animal random effect. Duroc sows produced 1.1 more PBA (p=0.03) than P sows. Significant heterosis effects were found for PBA (0.88 piglets, p=0.009) and for PW (0.72 piglets, p=0.03). Hybrid sows produced 1.43 and 1.15 piglets more than P sows, and 0.33 and 0.29 piglets more than D sows, born alive and weaned, respectively. No differences in other variables between genotypes were found. Heritability values (SE) were 0.13 (0.06) for PBA, 0.31 (0.08) for ABW, 0.14 (0.06) for PW, 0.17 (0.02) for AWW, 0.10 (0.01) for S and 0.08 (0.03) for WCI. Winter and spring farrowings resulted in heavier piglets at birth (p<0.001) and at weaning (p<0.01), but no effect on PBA, P and S was observed. Weaning-to-conception interval was greater in summer months (p<0.001). The results suggest seasonal reproductive behaviour. The local breed (P) compared well with a conventional one (D). Furthermore, the crossbred dam appeared attractive due to heterosis in litter traits.