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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.

The level of inbreeding in a population should be limited to avoid the inbreeding depression and maintain variability needed to assure long term genetic progress. Inbreeding coefficient (FPED) is usually calculated using pedigree information. Single nucleotide polymorphism (SNP) genotyping tools give the possibility to calculate genomic inbreeding parameters. The proportion of the autosomal genome covered by runs of homozygosity (ROH) can be used to estimate the level of genomic inbreeding (FROH). The breeding program of Italian pig breeds started about 25 years ago. In this work, we retrospectively analysed FROH over this period in Italian Large White (ILW) and Italian Duroc (ID) heavy pig breeds and compared this parameter with FPED. A total of 1,420 ILW and 572 ID pigs born over the last 25 years have been genotyped with the Illumina PorcineSNP60 BeadChip. ROH were identified with PLINK version 1.9, considering a minimum of 15 SNPs, and a minimum length of 1 Mbp. Then FROH was computed for all animals and averaged over all animals born by year. Averaged FROH over all considered years was higher in ID than in ILW and was constant over all analysed time window. FROH and FPED were parallel for both breeds over the same period. The results indicated that both FROH and FPED can be used to manage inbreeding levels in Italian heavy pig breeds.