INFLUENCE OF FETAL DEATH AND FETECTOMY ON GESTATION AND THE INITIATION OF PARTURITION IN THE EWE

Depressed function of the fetal hypothalamic-pituitary-adrenal axis re sults in prolonged gestation, and fetal death causes premature parturi tion. The objective of this experiment was to determine effects of dea th in utero of a sibling, or its removal, on the duration of gestation and concomitant changes in maternal serum concentrations of oestradio l (E) and progesterone (P). Ovine placental lactogen (oPL) was also de termined as an index of placental viability. Blood samples were collec ted in the morning, beginning 3 days prior to surgery on Day 115 +/- 3 of gestation and continuing daily until 3 days post partum. Surgeries were performed via mid-ventral laparotomy to induce fetal death or to remove the fetus. Fetal death was induced by ligating the umbilicus. Duration of gestation was similar (P > 0.05) in control (C, n = 6) and sham-operated (S, n = 3) ewes (148 +/- 1.0 and 148.6 +/- 0.7 days, re spectively). On the day of parturition, concentrations of P, E and oPL were 5.2 +/- 1.9 ng mL(-1), 135 +/- 22 pg mL(-1) and 153 +/- 54 ng mL (-1), respectively, in ewes from combined C and S groups. Total fetect omy (n = 3) resulted in a rapid decrease (P < 0.05) in maternal serum concentrations of P, E, and oPL. Ligation of the umbilicus of both fet us(es) in utero (n = 4) induced fetal death, decreased (P < 0.05) leng th of gestation to 118.8 +/- 1.8 days and decreased (P < 0.05) serum c oncentrations of P and oPL prior to parturition and oPL on the day of parturition. In addition, maternal serum concentrations of E failed (P > 0.05) to increase at parturition. Length of gestation and concentra tions of P, E and oPL at parturition were not affected (P > 0.05) by r emoval of one fetus when its sibling was undisturbed (n = 4) compared to control ewes. In contrast, death of one fetus with its sibling undi sturbed (n = 5) decreased (P < 0.01) length of gestation (139.2 +/- 2. 8 days), but did not affect P, E and oPL (P > 0.05) on all days tested . In conclusion, death of one fetus reduced the duration of gestation, but changes prepartum in maternal serum concentrations of P and oPL w ere similar to ewes delivering only live fetuses. The increase in mate rnal concentrations of E that normally occur at parturition was absent in ewes giving birth to only dead fetuses and, therefore, was not a p rerequisite to parturition.