The modern high-producing dairy cow is sub-fertile. Early embryo loss, within the first 16 days of gestation, is the greatest contributor to reproductive wastage (Sreenan et al., 2001), though the causes for this are not well understood. Nutrition plays a fundamental role in reproduction and specifically there is emerging evidence that supplemental polyunsaturated dietary fatty acids (PUFA) can increase cow fertility (Thatcher et al., 2006). For example, in-vitro studies suggest that the ω-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may be pivotal in the suppression of endometrial prostaglandin F2α synthesis, a critical regulator of luteolysis and hence embryo survival, though the biochemical pathways involved have not been elucidated. The objective of this study was to determine the effect of dietary supplementation of ω-3 PUFA on mRNA expression of key uterine endometrial genes involved in PGF2α biosynthesis.