Influence of estrogen receptor 1 (ESR1) genotypes on litter size, sow productivity, and performance test traits in a local marker-assisted selection program for Landrace and Large White pigs

Genetic improvement of litter size through marker-assisted selection (MAS) based on the estrogen receptor 1 (ESR1) gene is of considerable economic value to local pork producers. This study confirmed the favorable effect of ESR1 genotypes to improve litter size born alive (LSBA), litter size at weaning (LSW), and sow productivity index (SPI) of Landrace and Large White sows of the progeny generation produced in a MAS program adapted by a local nucleus breeding farm in the Philippines. Analysis of 581 litter records from 163 sows genotyped at the ESR1 locus showed that Large White sows with BB genotype had 1.56 more LSBA and 1.74 more LSW than those with AA genotype (P<0.05), with no significant effect (P>0.05) on piglet birth weight (BWT). Sow productivity index (SPI) for BB sows was 3.17 and 3.31 higher SPI for Landrace and Large White, respectively, than those for AA sows (P<0.05). Additive and dominance effect for LSBA in Large White sows was +0.78 and – 0.29, respectively. Favorable pleiotropic effects (P<0.05) were found in LSW at +0.57 and +0.88 for Landrace and Large White sows, respectively. There was no difference between ESR1 genotypes (P>0.05) in terms of farrowing interval, farrowing index, and teat number. For a local nucleus breeding farm that is constrained to initially determine ESR1 genotype of its replacement boars only, this study suggests prioritizing the use of replacement boars, sows with “BB” sire, and other high-SPI sows (i.e., SPI ≥ 24) with “AA” or “AB” sire with the favorable BB genotype to improve LSBA, LSW, and SPI.