Genetic Improvement of Sow Lifetime Productivity

Sow lifetime productivity is a complex trait that would benefit commercial populations if improved. Sows need to produce 3 litters to cover the cost of replacement; yet, nearly half of gilts retained for breeding are removed prior to producing 3 litters resulting in an economic loss. Longevity and lifetime productivity are complex phenotypes with numerous contributing factors resulting in low estimates of heritability. To facilitate selection for lifetime productivity, scientists have searched for genetic markers associated with improved performance as well as indicator traits that can be measured at an early age. Research has led to numerous marker associations of genetic variation in candidate genes with litter size as well as a discovery that gilts reaching puberty at an earlier age had a greater likelihood of producing 3 or more litters in a National Pork Board supported study. Commercial breeding companies have greatly increased litter size with traditional BLUP selection and have adopted genomic selection methodology. To unlock the genetic factors contributing to lifetime productivity, a principal component analysis was conducted, which included a number of key phenotypes associated with productivity. Phenotypes on 1,633 sows included lifetime number born, born alive and weaned, days in production, final parity, average litter birth weight, average litter weaning weight, age at puberty, day 140 weight and day 140 backfat measurements. Analysis indicated strong correlations among lifetime number of piglets born (total, alive and weaned) with final parity and days in the herd, moderate correlations among lifetime performance traits (pigs born and weaned) with average litter weights (birth and weaning) and virtually no correlation among lifetime performance and day 140 measurements or age at puberty in these data. Lack of association between age at puberty and lifetime performance is likely due to population management as all retained gilts reached puberty early. Genome-wide association analyses were performed using GENSEL for five principal components (PC1 – PC5) that describe the most variation. PC1 was the primary component affiliated with lifetime performance traits and accounted for 54% of the phenotypic variation. PC1 had a genomic heritability of 0.19 with marker associations residing on chromosomes 5, 12, 14, 15 and X. These results identified considerable genetic variation for sow lifetime performance indicating selection should be very effective at improving this trait. Genomic selection would enable ranking potential replacement animals early in life and increase the accuracy of selection.

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