Genetic analysis of functional and non-functional teats in a population of Yorkshire pigs

.Litter size is included in the goal of most pig breeding programmes. With an increased litter size, the number of functional teats, which are needed to achieve piglet weight gain and uniform litters, becomes increasingly important. The non-functional (e.g. inverted, blind, or small) teats might have a lower value for the nursing of the piglets. In Sweden, within the pig breeding company Nordic Genetics, the total number of teats, as well as the numbers of functional and non-functional teats, are recorded for purebred Yorkshire pigs both at 3 weeks of age (identity marking) and at about 5 months of age (performance testing). In 2010, 13% of the Swedish purebred Yorkshire pigs had at least one non-functional teat at performance testing (100kg live weight). The aim of this study was to analyse both genetic and phenotypic variation among the teat traits and to analyse the associations among the teat traits, age and sidefat thickness at 100kg live weight. In the phenotypic analyses there were significant differences between males and females for all analysed teat traits. Males showed a higher number of functional teats and females three times more non-functional teats at 100kg live weight. In the genetic analyses the records for males and females were treated as representing different traits. The estimated heritability of total number of teats and the number of functional teats, both at 3 weeks of age and at 100kg live weight, was in the range 0.36–0.42. The heritability of the number of non-functional teats at 3 weeks of age was low, 0.02, for both males and females. Surprisingly, at 100kg live weight, the heritability of non-functional teats was moderate, 0.29, for females, but still low, 0.03, for males. Further studies are required to investigate whether there is a biological explanation for this finding, or if there is a difference between the genders in the recording procedure of this trait. The only significant genetic correlation found between the teat traits and performance traits was for male pigs; the genetic correlation for the relationship between the number of non-functional teats at 3 weeks of age and the age at 100kg was −0.2. Thus, slowly growing pigs have a lower number of non-functional teats. Our results show that the teat number efficiently can be improved by selection. However non-functional teats is a complex trait and further studies need to be performed to investigate the possibilities to improve selection against the non-functional teats.