Delayed uterine clearance (DUC) is a significant problem contributing to subfertility and infertility in the mare, characterized by an accumulation of fluid and inflammatory debris in the uterine lumen following breeding events, venereal disease or an estral cycle. This syndrome is typically seen in older, multiparous mares and mares with poor reproductive tract conformation. The etiopathogenesis of DUC has not been fully elucidated but suggested causes include poor genital conformation, a cranioventrally tilted uterus, defective myometrial contractions, decreased intrauterine immune activity, inappropriate lymphatic drainage or mucus overproduction. The objective of this research was to evaluate gene expression of selected genes in endometrial tissue samples taken from three categories of mares (young fertile [YF], older clinically normal [ON] and older susceptible [OS]). The genes assayed in this research were oxytocin receptor, PGF2á receptor and progesterone receptor. The expression of each of these genes was normalized using the expression of two housekeeping genes, beta actin and ribosomal 18S RNA. Quantitative real-time polymerase chain reaction (QPCR) was used to evaluate gene expression of the selected genes. Results indicated that there was no statistically significant difference in the expression of any of the three experimental genes among any of the three categories of mares. From this research, the direction of further research regarding the pathogenesis of DUC can be made: myometrial tissues can be assayed for similar genes, the expression of other genes regulating myometrial contraction can be assayed or the expression of uterorelaxants can be studied. / Master of Science