Genetic and clinical studies of teat traits in the pig

A major goal of pig breeding is to produce sows with good longevity, which can raise many uniform litters with healthy, fast-growing piglets. The fitness of the sow, including the presence of sufficient number of functional teats, is one key to the success of the initial rearing period of the piglets. A frequently occurring type of non-functional teat, believed to not deliver sufficient amounts of milk from which piglets cannot suckle easy which is thereby less valuable for the suckling piglets, is the inverted teat. The aim of this thesis was to provide new genetic and clinical knowledge about pig teat traits, to create implements for accurate registrations and optimum focus on these traits in the breeding work. The long term aim is to provide knowledge that contributes to an increased piglet survival and a higher daily piglet growth. The present study shows that many of the inverted teats will protrude between the age of 5 month and early gestation. However, some teats remain inverted and neither inverted teats nor small teats will supply enough milk to the suckling piglets and they are therefore undesired. At three weeks of age the number of functional and non-functional teats is the same between male and female pigs. However this changes at live weight of 100 kg and the number of functional and non-functional teats differs between gender. The difference noted may be caused by differences in the recording because of, e.g. divergent development during puberty. Total teat number, number of functional teats and inverted teats are heritable traits and the number of functional teats can therefore be improved by selection. There is no significant genetic correlation between litter size and teat number. This motivates that the number of functional teats should be included in any genetic evaluation which includes litter size. Present study has identified tentative chromosome regions for the total number of teats, the number of inverted and number of functional teats. Further research is needed to fine-map and verify the candidate genes. This thesis has assisted in answering important questions regarding teat traits in the pig. The complexity of the interaction between the nursing sow and its piglets was further emphasized, but there are still questions that need to be focused and new questions have been raised.