Genetic association between leg conformation in young pigs and sow reproduction

Lameness is an issue of concern in pig production due both to animal welfare and to economical aspects. Lame sows are believed to suffer from pain and stress which is reported to have a negative influence on reproduction. Leg conformation and locomotion traits in young animals are associated with the risk of lameness at higher age. The purpose of this study was to estimate the genetic parameters of leg conformation traits recorded at performance testing (around 5 months of age) and their genetic correlations with reproduction traits. Information on leg conformation traits from 123,307 pigs scored and on reproduction traits from 22,204 litters in the first and second parity from Swedish Yorkshire nucleus herds were available for genetic analysis. Eight conformation and locomotion traits, coming from the old or the new scoring system in Sweden, included old movement, old overall leg score, new movement, new toes quality, new front leg quality, new rear leg quality, standing-under-position syndrome and new overall score. Four reproduction traits were analyzed by parity: the number of total born piglets, the number of liveborn piglets, the number of stillborn piglets and weaning to service interval. Estimates of heritabilities and genetic correlations between traits were obtained using a multi-trait linear animal mixed model. The heritability estimates were low to moderate, ranging from 0.02 to 0.20 for conformation traits and from 0.06 to 0.10 for reproduction traits. Significant genetic correlations were found between new toes quality and new overall score and the number of liveborn piglets in the 1st parity (−0.35 and −0.31, respectively), indicating that sows with even toes and better overall leg score tend to have higher number of liveborn piglets. Old movement score showed significant correlations with number of total born and number of liveborn piglets in both parities (0.20 to 0.36) and with weaning to service interval in the 2nd parity (−0.35±0.11). Similarly, standing-under-position syndrome was highly associated with number of total born and number of liveborn piglets in both parities (−0.54 to −0.35), indicating that sows with better movement and not suffering from standing-under-position syndrome are likely to have larger litter size and shorter interval to return heat after weaning. Heritabilities and significantly favorable genetic correlation estimates suggest the possibility of simultaneous improvement of both leg quality and reproduction performance by selecting on sound leg conformation and locomotion of young pigs.