Sex chromosome mosaicism and infertility in mares.

From the standpoint that cytogenetic screening in mares is seldom necessary as an aid to diagnosis of the gonadal dysgenesis syndrome, a series of double-blind trials were conducted to test the proposal that present practice failed to explore the potential for cytogenetics in clinical practice. It was demonstrated that diagnoses of infertility might be made where mares were found to be of normal phenotype by clinical examination. Such mares were found to be gonosmic mosaics. One stallion had a polymorphism of the X chromosome and had poor conception rates. It was demonstrated that the true value of chromosome testing in clinical stud practice has previously been misinterpreted and underestimated.