[Cytogenetical and molecular analyses in a horse with SRY-negative sex reversal]

Numerical and structural aberrations of chromosomes may cause malformations, embryonal losses and reduced or missing fertility. In male horses the fertility is rather well controlled through their semen evaluation. For mares there are no mandatory regulations which specify their use in a breeding programme. Therefore, mares with chromosomal aberrations, which exclude reproduction success may be chosen for breeding. The present case describes a horse, offically registered as a female, which was presented for a breeding exam. On this occasion, small and inactive ovaries were diagnosed. Although the cytogenetical analysis excluded a numerical or gross structural chromosome aberration, the karyotype (64,XY) corresponded to the male sex. The diagnosis male to female sex-reversal (SRY-negative) excludes reproductive success for this horse. This case underlines the importance of a cytogenetic analysis for female horses, before they enter a breeding programme.