Luteal support of pregnancy in red deer (Cervus elaphus): effect of cloprostenol, ovariectomy and lutectomy on the viability of the post-implantation embryo

In two experiments with red deer hinds we investigated (1) the sensitivity of the corpus luteum of pregnancy and the post-implantation embryo to a single injection of a prostaglandin analogue, and (2) the effects of removal of ovarian and luteal tissues on the maintenance of pregnancy. In the first experiment, groups of hinds (n = 6 per group) were given a single intramuscular injection of cloprostenol on either Day 30, 40 or 60 of pregnancy, with fetal viability assessed by repeated rectal ultrasonography and luteal status assessed by measurement of plasma progesterone concentrations. Control hinds (n = 5 or 6) received saline injections at the same stages of pregnancy. Pregnancy was maintained to term in all control hinds. However, 918 (50%) of cloprostenol treated hinds aborted 48–120 h after injection, at a frequency of 36 on Day 30, 56 on Day 40 and 16 on Day 60. All hinds receiving cloprostenol exhibited a marked decrease in plasma progesterone concentrations within 12 h of injection, although those that maintained pregnancy appeared to undergo luteal recovery 56–72 h later. In the second experiment, groups of hinds (n = 3 or 4 were subjected to either ovariectomy, lutectomy or sham surgery on Day 33 or 75 of pregnancy. Contemporary controls were included in the trial. Fetal viability was assessed by rectal ultrasonography and recovery of reproductive tracts at hind slaughter 30 days after surgery. Plasma progesterone concentrations were measured during this period. Ovariectomy and lutectomy resulted in fetal loss at both stages of pregnancy. Although one hind lutectomised on Day 75 retained pregnancy until slaughter (30 days after surgery), the fetus appeared to be developmentally retarded relative to those retrieved from control and sham-operated hinds. Both ovariectomy and lutectomy resulted in a marked decline in plasma progesterone concentrations. studies have indicated that the presence of luteal tissue is important for pregnancy maintenance in the first 75 days of gestation in red deer. However, the corpus luteum of pregnancy exhibits a degree of refractoriness to the luteolytic (and hence, abortificient) effects of cloprostenol.