A SURVEY OF SEX-CHROMOSOME ABNORMALITIES IN 204 MARES SELECTED FOR BREEDING

Cytogenetic testing was done on 204 mares for sex chromosome abnormali ties. Cases were selected based on owner identification of the animal as a mare they would be willing to invest resources in to breed. Virgi n mares or mares in their first year at stud were included, regardless of breed or age. Karyotype evaluation was done on routine Giemsa stai ned and C-banded metaphase chromosomes. Findings included, 201 (98.5%) 64, XX normal mares, 1 (0.05%) 63X, /64,XX mosaic mare, 1 (0.05%) 64, XY sex reversed mare and 1 (0.05%) 65, XXX trisomy mare. The overall occurrence of sex chromosome abnormalities in the group of mares studi ed was 1.5%. Based on the occurrence of abnormalities in our study, we suggest the prevalence of sex chromosome abnormalities in mares is <3 %.