LUTEAL SUPPORT OF PREGNANCY IN RED DEER (CERVUS-ELAPHUS) - EFFECT OF CLOPROSTENOL, OVARIECTOMY AND LUTECTOMY ON THE VIABILITY OF THE POSTIMPLANTATION EMBRYO

In two experiments with red deer hinds we investigated (1) the sensiti vity of the corpus luteum of pregnancy and the post-implantation embry o to a single injection of a prostaglandin analogue, and (2) the effec ts of removal of ovarian and luteal tissues on the maintenance of preg nancy. 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 r ectal ultrasonography acid luteal status assessed by measurement of pl asma progesterone concentrations. Control hinds (n = 5 or 6) received saline injections at the same stages of pregnancy. Pregnancy was maint ained to term in all control hinds. However, 9/18 (50%) of cloprosteno l treated hinds aborted 48-120 h after injection, at a frequency of 3/ 6 on Day 30, 5/6 on Day 40 and 1/6 on Day 60. All hinds receiving clop rostenol exhibited a marked decrease in plasma progesterone concentrat ions within 12 h of injection, although those that maintained pregnanc y appeared to undergo Luteal recovery 56-72 h later. In the second exp eriment, groups of hinds (n = 3 or 4) were subjected to either ovariec tomy, lutectomy or sham surgery on Day 33 or 75 of pregnancy. Contempo rary 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 w ere measured during this period. Ovariectomy and lutectomy resulted in fetal loss at both stages of pregnancy. Although one hind lutectomise d 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 l utectomy resulted in a marked decline in plasma progesterone concentra tions. These studies have indicated that the presence of luteal tissue is important for pregnancy maintenance in the first 75 days of gestat ion in red deer. However, the corpus luteum of pregnancy exhibits a de gree of refractoriness to the luteolytic (and hence, abortificient) ef fects of cloprostenol.