Effect of Estrogen Receptor (ESR) Genotypes on Litter Size and Weaning to Estrus Interval in a Thai Commercial Swine Population

Estrogen receptor (ESR) locus is known as genetic marker for improving litter size (LS) in swine. However, achievement of selection using this maker should be considered for other reproductive traits. Furthermore, weaning to estrus interval (WEI) is an economically important trait and it has been frequently examined for reproductive performance of the sows in subsequent litters. Thus, the objectives of this study were to examine factors affecting LS and WEI of a commercial swine population, and evaluate the effect of ESR genotype on LS and WEI. A total of 1,377 litter records from 346 sows (120 Landrace; 118 Yorkshire; 23 Landrace × Yorkshire crossbreds and 85 Yorkshire × Landrace crossbreds) were collected from January 2005 to December 2009. The ESR genotypes were determined using PCR-RFLP. The polymerase chain reaction was used to amplify 120 bases of the target ESR fragment and then they were digested by restriction enzyme PvuII. The ESR genotypic frequencies were 0.6965, 0.2601 and 0.0434 for AA, AB and BB genotype, respectively. The dataset was analyzed using a linear model, which included ESR genotype, breed group of sow, year-season of farrowing, and parity as fixed effects and random effect was residual. Year-season of farrowing, breed group of sow and parity had significantly effect on LS and WEI (p<0.05). Landrace sows produced larger LS (10.64 ± 0.29 piglets) and returned to estrus (5.45 ± 0.65 days) faster than the other breed groups. Prolong WEI (8.60 ± 0.58 days) was found in the first parity sows, while the third parity sows produced the largest LS (10.80 ± 0.33 piglets). The ESR genotype was not significantly effect on LS and WEI. However, sows with the BB genotype performed the highest LS (10.50 ± 0.47 piglets) and the shortest WEI (5.97 ± 1.07 days). Thus, improving LS of the replacement sows in this population by using marker-based selection, B allele of the ESR gene, would positively associate with WEI