RESUMEN
The aim of our study was to diagnose aneuploidy in equine spermatozoa by multicolour fluorescence in situ hybridization (FISH) technique using specific molecular probes for equine sex chromosomes and autosome pair four (EGFR probe) labeled by different fluorochromes. These were applied on decondensed spermatozoa of four stallions. In total, more than 8800 sperm cells were examined. The total frequency of aberrant cells was 0.496%: aneuploidy of XX (0.135%), YY (0.023%), XY (0.102%), diploidy (0.057%), lack of sex chromosome (0.18%). In one stallion the ratio of normal X- and Y-bearing cells was different from the expected 1:1 ratio (p = 0.0002), in all three other stallions this ratio was close to 1:1. The present study demonstrated that the FISH technique is a powerful method to identify sex chromosome aberrations in equine spermatozoa and allows for the determination of the ratio between X-Y-spermatozoa.