Teat number parameters in Italian Large White pigs: Phenotypic analysis and association with vertnin (VRTN) gene allele variants

Teat number (TN) is a major determinant of the mothering ability of sows that in turn influences their reproductive efficiency. Even if the total number of teats is routinely recorded in many pig breeding programs, its individual side count is not commonly recorded and just few investigations have evaluated the bilateral symmetry of this morphological trait. Several studies in pigs have identified genes or genomic regions affecting teat traits. For example, polymorphisms in the vertnin (VRTN) gene have been associated with the number of thoracic vertebrae and with TN in a few pig breeds. In this study, we evaluated the phenotypic variability of traits related to teat count including number of teats on the left (LTN) and right (RTN) side, TN, maximum number of teats between the two sides (MAX) and teat asymmetry traits (signed and absolute difference between RTN and LTN) in 793 Italian Large White heavy pigs. Furthermore, we genotyped these pigs for the AB554652:g.20311_20312ins291 VRTN gene polymorphism and evaluated its effect on the recorded teat parameters. This polymorphism was significantly associated (P < 0.0001) with all investigated traits, except the asymmetry traits. The estimated additive effects were 0.35 for TN, 0.19 for RTN, 0.16 for LTN and 0.17 for MAX, with a favorable effect of the mutated Q allele (the allele derived by the inserted 291 bp fragment). Selection for the VRTN Q allele could expedite the genetic progress for teat number and thus might be important to improve reproduction performances of the Italian Large White heavy pig breed.