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To address whether altered erythropoietin (EPO) synthesis might be involved in prenatal pig mortality, studies were conducted to measure porcine embryonic EPO mRNA expression during early gestation (days 24–40). Three pig models differing in embryonic survival from days 24–40 were investigated: intact white crossbred gilts (INT), white crossbred gilts that were unilaterally hysterectomized-ovariectomized before puberty and whose pregnant uterus constituted a crowded environment (UHO), and prolific, intact Meishan gilts (ME). A partial cDNA for porcine EPO, developed via reverse transcription and polymerase chain reaction procedures was used to generate a 32P-labeled probe for use in Northern analyses. In an initial study, embryonic liver EPO mRNA was greatest on day 24, decreased by day 30 (P < 0.01), and was barely detectable by day 40. EPO mRNA expression was not influenced by pig model. Placental EPO mRNA expression was detectable in only 4 of 53 placentae examined. In a second study at day 35 of gestation, embryonic liver EPO mRNA expression was measured in the same three pig models and in two embryos of divergent weights from each gilt. Meishan embryos had lower (P <0.01) plasma immunoassayable EPO concentrations (P = 0.04) and higher survival rates (87 ± 2.7%) at day 35 than did white crossbred embryos (75±5%). Liver EPO mRNA expression did not differ among animal models, nor did plasma EPOor tissue EPO mRNA expression differ between large and small embryos. There was no apparent relationship between embryonic development, measured as embryonic and placental size, and plasma EPO concentrations or liver EPO mRNA expression. These results indicate that at the gestational ages examined, the embryonic liver is one source of plasma erythropoietin and suggest that at the ages sampled, EPO is not a limiting factor in embryonic development.