ESR1 and ESR2 gene markers are not associated with number of piglets born alive in Italian Large White sows

Many studies have reported that markers in the estrogen receptor 1 (ESR1) and estrogen receptor 2 (ESR2) genes are associated with litter size in pigs, even if inconsistent results have been obtained in different populations. We analysed the ESR1 PvuII and the ESR2 AF164957:c.949G>A polymorphisms in Italian Large White (ITLW) sows to evaluate if these markers are associated with number of piglets born alive at first litter (NBA1). First, both polymorphisms were genotyped by selective genotyping in a total of 440 sows chosen according to the extreme and divergent estimated breeding value (EBV) for NBA1 (220 sows with low EBV and 220 sows with high EBV). For the ESR1 polymorphism, no allele and genotype frequency differences were observed between the two groups (allele A= 0.62 and allele B= 0.38 in both two groups). For the ESR2 polymorphism, a trend of different allele frequency between the two tails was identified (P = 0.052). However, no significant association between the same ESR2 marker and EBV NBA1 was detected analyzing 1772 ITLW sows (allele A= 0.59 and allele G= 0.41). As the two investigated polymorphisms were not associated with NBA1 EBVs, they seem not useful for marker assisted selection to improve this trait in the ITLW breed