CONICET | Buscador de Institutos y Recursos Humanos

Chromosomal abnormalities are one of the most underestimated causes of non-explained infertility in the horse. Despite the fact that some studies demonstrated a prevalence near to 2% in certain populations, this kind of genetic disease is normally ignored in cases of individuals with reproductive problems. Blood chimerism of the sexual chromosomes was described in horses [1]. Despite the fact that in none of those cases gonads or genital tracts were abnormal, some authors suggested that those chimeric individuals could be sub-fertile and have problems to become pregnants [2]. Those animals could be characterized by molecular methods (STR markers and sexually related PCR determinations ) in a quick and efficient way, avoiding the use of karyotyping, which was described as a difficult and time-consuming tool [3]. In total, 21 STR markers and two PCR fragments were used in this diagnostic technique. Eight of them were related to the sexual chromosome pair (5 to ECAX, 2 to ECAY and one to both chromosomes). DNA from blood and hair samples were obtained and analyzed according to our protocols. The number of alleles obtained in the STR markers allowed to us to differentiate the normal animals from the chimeras. Differences between the samples of the same individual determined the presence of true (full body) or blood chimerism. In this study, we diagnosed the presence of 6 cases (5 mares and 1 stallion) with sexual leukocitic chimerism in the Purebred Spanish horse breed. Interestingly, none of them has been reported as a result of a twin gestation or foaling. Morphologically, all the animals were described as externally and internally (rectal palpation and eco) normals. Moreover, four of them had produced foals during his lifetime (3 mares and one stallion) and the other two mares were passed the reproductive inspection of the PRE breeders association. Molecularly, all the individuals showed differences between the samples obtained from blood (abnormal allelic pattern and male-like results in the sexual markers) and hair (normal allelic pattern and correct sex determination) DNA, determining a leukocitic chimerism. The present study showed that, at least in the PRE breed, all the equids diagnosed as chimeric were fertile and did not show any other kind of morphological and physiological abnormality. Considering that the percentage of twining in mares can be up to 2% [4], we suggest that a higher percentage of chimeric horses remains undiagnosed. Due to this, the application of screening programs using these methodologies could help to determine conclusively the real effect of blood chimerism in the reproduction of the horses.