Single-SNP and haplotype-based genome scans for teat number in Italian Large White and Landrace pigs

Teat number (TN) is an important parameter for the mothering ability of the sows. Being an economically relevant reproductive trait, TN is the objective of genetic selection which generally impose a minimum threshold value in breeding programmes. Several studies investigated TN in different pig populations, reporting high variability (from 8 to 21 teats), a medium/high heritability (from 0.10 to 0.70) and a polygenic control of the trait. We previously investigated TN in Italian Large White (ILW) pigs and associated its variability to polymorphisms in the VRTN gene. Here, we refined those results in a population of about 4,000 ILW pigs genotyped with the 70K GGP Porcine BeadChip. Moreover, about 2,000 Italian Landrace (ILA) pigs were for the first time investigated. Single-SNP and haplotype-based genome scans were performed via linear mixed model analyses (GEMMA tool). TN for the ILW pigs was in the range 12-20, whereas ILA pigs had 10-18 teats. The two populations had about 53.4 and 43.5% of animals with more than 14 teats, respectively. Genomic heritability of TN was 0.30 (ILW) and 0.38 (ILA). We identified a total of 22 quantitative trait loci (QTL) on 12 porcine chromosomes associated with TN variability in these two populations. Obtained results confirmed the association of the VRTN gene variants in the ILW population and pointed out other genome regions harbouring QTLs for reproductive traits (e.g. litter size, number of vertebra as reported in other populations). ILA pigs showed a completely different set of genome variants affecting TN. Overall, these results provided information that could be used to design breeding programmes to improve TN in Italian pig breeds.