Association and haplotype analysis of candidate genes in five genomic regions linked to sow maternal infanticide in a white Duroc x Erhualian resource population

Background: Maternal infanticide is an extreme and failed maternal behavior, which is defined as an active attack on piglets using the jaws, resulting in serious or fatal bite wounds. It brings big economic loss to the pig industry and severe problems to piglets' welfare. But little is known about the genetic background of this behavior. Quantitative trait loci (QTL) for maternal infanticide were identified in a White Duroc x Erhualian intercross by a non-parametric linkage analysis (NPL) in our previous study. In this study, associations of 194 microsatellite markers used in NPL analysis with maternal infanticide behavior were further analyzed by transmission-disequilibrium test (TDT). On this basis, seven genes (ESR2, EAAT2, BDNF, OXTR, 5-HTR2C, DRD1 and GABRA6) at five genomic regions were selected and further analyzed. Associations of single nucleotide polymorphisms (SNPs) and haplotypes in each gene with maternal infanticide behavior were evaluated. Results: Microsatellite markers on pig chromosome (SSC) 2, 13, 15, and X displayed significance at P < 0.05 by both TDT and NPL. Of the seven candidate genes, three ESR2 SNPs had nominal evidence for association (P < 0.05). Allele A at EAAT2 g. 233G > A and allele T at DRD1 g.1013C > G > T also showed evidence of overtransmission to infanticidal sows. In the overall tests of association of haplotypes, candidate genes of ESR2, EAAT2 and DRD1 achieved overall significance level (P < 0.05). Haplotype [A; A; G], [G; A; G], [A; G; G] and [C; C], respectively, from ESR2, EAAT2 and DRD1 showed higher frequencies to infanticidal sows (P < 0.05). Alleles among haplotypes and SNPs which showed an overtransmission to infanticidal sows were from White Duroc. Conclusions: From association tests of SNPs and haplotypes, ESR2, EAAT2 and DRD1 showed significant associations with maternal infanticide. This result supported the existence of QTL for maternal infanticide behavior on SSC1, SSC2 and SSC16.