Association between ESR1 and RBP4 genes and litter size traits in a hyperprolific line of Landrace × Large White cross sows

This study was aimed at analysing single-nucleotide polymorphisms in the oestrogen receptor 1 (ESR1) and retinol-binding protein 4 (RBP4) genes in a hyperprolific line of Landrace × Large White (Topigs 20) cross sows (n = 101). The following litter size traits were analysed: total number born, number of born alive and number of weaned piglets. ESR1 and RBP4 genotypes determined on the basis of single-nucleotide polymorphisms were analysed using the least square method with the GLM procedure in SAS with eight effects. The REG procedure was used to calculate the effects of the additive and dominance components. The second parity sows with ESR1 BB genotype had a significantly higher (P < 0.05) number of weaned piglets compared to AB, with a tendency towards difference (P < 0.1) between homozygotes for number of born alive and number of weaned piglets. In the case of the RBP4 gene, the first parity sows of the AA genotype had a significantly higher total number born (P < 0.05) compared with the BB genotype, with a tendency towards difference (P < 0.1) between AA and heterozygotes for total number born, and homozygotes for number of born alive. The BB genotype showed a tendency for higher number of weaned piglets (P < 0.1) as compared with the AA genotype in the third parity sows for the RBP4 gene. In all parities, significant effects (P < 0.05) of parity were recorded for total number born, number of born alive and number of weaned piglets, season of farrowing for total number born, and the ESR1 and RBP4 interaction for number of born alive. In the first parity sows, significant effects (P < 0.05) on total number born were determined for gene interaction and gestation length, the latter also being recorded in the second parity sows. The additive (a) effect of single-nucleotide polymorphisms in RBP4 was significant (P < 0.05) for total number born in all parities as well as in the first parity sows, and dominance effect (d) (P < 0.05) of single-nucleotide polymorphisms in ESR1 for number of weaned piglets in the third parity sows. The obtained results regarding the investigated genes could help to provide a better understanding of the effect of single-nucleotide polymorphisms on litter size and thus promote genetic progress in pig reproduction management.