Genetic variability within French race and riding horse breeds from genealogical data and blood marker polymorphisms

Abstract

The genetic variability of five horse breeds raised in France was analysed: Thoroughbred, Trotteur Français, Arab, Anglo-Arab and Selle Français. Genealogical data and genotypes at seven blood group and nine protein loci were used. Paternal family sizes were found to be unbalanced, especially in Trotteur Français, Selle Français and Thoroughbred. Average coefficients of inbreeding for offspring born from 1989 to 1992 were 1.02 (Thoroughbred), 1.86 (Trotteur Français), 3.08 (Arab), 1.17 (Anglo-Arab) and 0.70% (Selle Français). High individual coefficients (> 6.25%) were found in substantial proportions only in Arab, where such high values represent one fifth of the total individual coefficients. Inbreeding was analysed according to the number of generations of ancestors considered. The results revealed the importance of close inbreeding in Arab and remote inbreeding in Thoroughbred. Arab was the only breed that showed evidence for a substantial amount of mating between close relatives. From 1974 to 1992. the rates of inbreeding, in percentage points per year, were +0.026 (Thoroughbred), +0.052 (Trotteur Français), +0.071 (Arab), +0.029 (Anglo-Arab) and +0.024 (Selle Français). The distribution of genetic contributions of founder animals was found to be unbalanced, especially in Trotteur Français where 25 founder animals only accounted for half the actual gene pool. No significant time-trend was found for blood markers allelic frequencies. The mean heterozygosity was highest in Trotteur Français and Selle Français and lowest in Thoroughbred and Anglo-Arab. The meaning of recent trends for genetic variability is discussed. The need for equalizing paternal family sizes in the future is outlined.