Effects of Long Term Selection in the Border Collie Dog Breed: Inbreeding Purge of Canine Hip and Elbow Dysplasia

Pedigree data of 13 339 border collie dog was collected along with hip and elbow dysplasia records (1352 CHD and 524 CED), and an inbreeding-purging (IP) model was created to detect possible purging. Ancestral inbreeding coefficients were calculated by gene dropping simulation method (Ballou, 1997; Kalinowski, 2000) with GRain 2.0 (Baumung et al., 2015) software. GLMM models were created to the examined traits fitted with a log-link Poisson distribution, added to the estimated values of classical inbreeding coefficient (F_W), and the ancestral inbreeding (F_BAL, F_KAL, F_KAL_NEW) as covariates. The effective population size decreased in the examined period along with the increase of F_W however, slight differences were found as a consequence of breeding dog imports. CHD values were getting lower by the expansion of F_BAL as the alleles were inbred in the past. For CHD signs of purging were obtained. There was a positive trend regarding the breeding activity (both sire and dam of the future litters should be screened and certified free from CHD and CED), as years of selection increased the frequency of alleles with favorable hip and elbow conformation. Division of the ancestral inbreeding coefficient shows that alleles IBD for the first time (F_KAL_NEW) had a negative effect on both traits, while F_KAL shows favorable results for alleles IBD in the past generations. Some authors had proven this phenomenon in captive populations or experimental conditions however, no evidence of inbreeding purge has ever been described in dog populations. Despite the various breeding practices, it seems, that alleles of these polygenic disorders could be successfully purged out of the population with long term selection.