Caughey et al (2005) reported that prostaglandins derived from omega 3 sources eicsapentaenoic acid (EPA C20:5) and docosahexaenoic acid (DHA C22:6) have different properties to those derived from the preferred substrate, arachidonic acid (ARA C20:4; n-6). Armstrong et al (2006) demonstrated that PGE2 increased progesterone when porcine granulosa cells were cultured in vitro with hCG. We hypothesized that PGE3 which is derived from EPA will produce a lower steroidogenic response as progesterone from isolated granulosa cells collected from pre-ovulatory sow ovaries. Ovaries were collected from slaughtered sows and follicles between 3–8 mm were aspirated and through a series of wash steps in HTCM (Hepes TCM 199). Mid-sized granulosa cells were recovered in a solution of BTCM (bicarbonate TCM) containing IGF-1. 0.5 × 106 cells/mL were cultured in 250 µL of Control (BTCM only), PGE2 or PGE3 (320 ng/mL in BTCM, Cayman Chemical Co.) treatments with IGF1 at 25 ng/mL. Cultures were incubated for 22 h at 38oC. Cultures were centrifuged and the supernatant was analysed in duplicate for progesterone. Data was analysed by Univariate GLM ANOVA. There was no significant difference between PGE2 and PGE3 treatments, however the main effect of PGE significantly increased progesterone production relative to the control (P = 0.017). Granulosa cells cultured with omega 3 derived PGE3 did not produce significantly lower progesterone levels than those with PGE2. We conclude that both PGE2 and PGE3 promote a steroidogenic response in cultured porcine granulosa cells. (1) Armstrong DT, Formosa, ER, Amato F, Schultz SJ. 2006. Prostaglandin E2 up-regulates luteinizing hormone receptor (LHR) expression and enhances steroidogenic responses of follicle cells.(2) Caughey GE, James MJ, Cleland LG. 2005. Prostaglandins and leukotrienes. pp. 42–49. In ‘Encyclopaedia of Human Nutrition. Vol. 4’. (Eds B Caballero, L Allen, A Prentice).