Accommodating Variable Disease Challenge on Breeding Value Prediction for Sires - Using Footrot as an Example

Footrot is a highly contagious hoof disease of sheep, the expression of which depends on environmental conditions and the presence of infective strains of bacteria. Footrot scored from field exposure is, therefore, a potentially difficult trait to analyse across time and production environments. This study explores the use of pre-analysis transformation techniques to account for the disease incidence and pattern of scores obtained, using footrot as an example. A biological transformation, where the phenotypes were transformed to a similar incidence level based on a nonlinear transition of scores over time produced the highest rank correlation of the sire's breeding values across challenges compared to more traditional statistical transformation techniques. The results suggest that using a transformation based on biological information is likely to improve the estimation of breeding values for footrot.