Abstract
Statistical analysis was conducted on sow stillbirth traits of three genotypes with 2,400 litters including the Erhualian, Large White and the F 1 cross of these two breeds. Number of stillborn piglets per litter in the Erhualian, Large White and the F 1 averaged 0.85, 0.31 and 0.70, and percentage bom alive averaged 95.0%, 97.0% and 95.5%, respectively. Erhualian sows with a greater litter size also had a higher stillbirth rate. Results of analysis of variance indicated that genotype, parity, farrowing year×farrowing season interaction and total number bom had highly significant effects on both number of stillborn piglets per litter and percentage born alive in sows (p 0.05), and highly significant effect on percentage born alive (p<0.01). Farrowing season had highly significant effects on both number of stillborn piglets per litter and percentage bom alive (p<0.01). From parity one to parity ten, least squares means for number of stillborn piglets per litter progressively increased with increasing parity and least squares means for percentage bom alive progressively decreased with increasing parity. Sows that farrowed in winter had the highest number of stillborn piglets per litter and the lowest percentage bom alive, sows that farrowed in autumn had the lowest number of stillborn piglets per litter and the highest percentage born alive. With increasing total number born, least squares means for number of stillborn piglets per litter markedly increased and least squares means for percentage born alive markedly decreased. Results from analysis of paternal half sibs indicated that the heritabilities for number of stillborn piglets per litter and percentage born alive were 0.110 and 0.124, and the genetic, phenotypic and environmental correlations between them were -0.989, -0.951 and -0.948, respectively. These results indicated that number of stillborn piglets per litter and percentage born alive were traits with the similar genetic background.
Highlights
Improving sow productivity is a major way to raise the economic efficiency of pig production systems (Yen et al, 1987)
Statistical analysis The mathematical model used to estimate the effects of genotype, parity, farrowing year, farrowing season and total number born on sow stillbirth traits was as follows: yijklmn = μ+Mi+Pj+Yk+Sl+(Y×S)kl+Nm+eijklmn
The genetic, phenotypic and environmental correlations between Number of stillborn piglets per litter (NSB) and percentage born alive (PBA) were -0.989, -0.951 and -0.948, respectively. These results indicated that NSB and PBA were traits with the similar genetic background
Summary
Improving sow productivity is a major way to raise the economic efficiency of pig production systems (Yen et al, 1987). Stillbirths constitute a major source of economic loss for the producer as well as an ethical problem (Leenhouwers et al, 1999). Risk factors for stillbirths in swine farms are parity, breed, sow body condition, use of oxytocin during parturition, obstetric intervention through vaginal palpation, farrowing duration, mummified fetuses, total litter size and litter birth weight (Lucia et al, 2002). The objectives of the present study were to evaluate the effect of genotype, parity, farrowing year, farrowing season and total number born on sow stillbirth traits and to estimate genetic parameters for sow stillbirth traits
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