Conservation of animal genetic resources in horses: The case of the Skyros small-horses

The main objective of conservation is the preservation of genetic diversity. Several tools are available to measure the genetic variability. In this study, we have used principally the relationship (and inbreeding) coefficients and the information given by the study of genetic markers. With a total population size lower than 200 individuals, the Skyros small-horse may be called a small population. It is thus a good example of population concerned by the management of genetic variability. In this study, the ‘studbook’ of the Skyros small-horse comprising a total of 395 individuals was analyzed in order to evaluate its genetic variability amongst other things. Only 6 ancestors were necessary to explain 50% of the genetic variability of the breed. Then genetic diversity within the Skyros breed was evaluated, at the genome level, using 16 microsatellites. A relatively high level of genetic variability within the breed was observed in terms of high values of mean effective number of alleles (3.3), observed heterozygosity (0.635), expected Levene’s heterozygosity (0.642), expected Nei’s heterozygosity (0.639), and polymorphism information content (0.617). This study demonstrated the existence of substantial genetic diversity in the Skyros small-horse population. Finally, one part of a conservation program is the establishment of a good mating plan (coupling of less related individuals). Relationships were thus estimated using a new estimator, which combines pedigree and markers information. Compared to other estimators, this combined estimator showed interesting results (inter alia, higher percentage of information explained by the 3 principal factors in the principal components analysis (46.22%)). Hence, the resulting estimated relationships were used to make proposals for the management of the breed.