Sex chromosome aberrations are known to cause congenital abnormalities and unexplained
infertility in horses. Most of these anomalies remain undiagnosed because of the complexity
of the horse karyotype and the lack of specialized laboratories that can perform such diagnoses.
On the other hand, the utilization of microsatellite markers is a technique widely
spread in horse breeding, mostly because of their usage in parentage tests. We studied the
usage of a novel combination of diagnostic approaches in the evaluation of a very uncommon
case of chromosomal abnormalities in a Spanish purebred colt, primarily detected using a
commercial panel of short tandemrepeat (STR)makers. Based on these results, we performed
a full cytogenetic analysis using conventional and fluorescent in situ hybridization techniques
with individual Equus caballus chromosome X and Equus caballus chromosome Y painting
probes. We also tested the presence of two genes associated with the sexual development in
horses and an extra novel panel of eight microsatellite markers specifically located in the sex
chromosome pair. This is the first case report of a leukocyte chimerism between chromosomally
normal (64,XY) and abnormal (63,X0) cell lines in horses. Our results indicate that
the use of the short tandem repeat markers as a screening technique and as a confirmation
utilizing cytogenetic techniques can be used as a very interesting, easy, and nonexpensive
diagnostic approach to detect chromosomal abnormalities in the domestic horse