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MEREDITH J. CLARK

Summary.

Injection of progesterone into lactating red kangaroos terminated embryonic diapause while the young continued to occupy the pouch. On Day 4, after progesterone injection on Days 1 to 3, the number of cells in the blastocysts was greater than during diapause and some glandular development had occurred in the uterus. By Day 8 the blastocysts had increased in size and the uteri were well developed.

When pouch young were removed (rpy) on Day 4 after injection of 10 mg progesterone/day on Days 1 to 3, the average time from rpy to birth in nine animals was shorter than in non-injected or in control-injected animals. The time from rpy to oestrus was similar in all groups. Not all animals gave birth earlier than expected, and at higher and lower dose levels the response was similarly heterogeneous. Two animals gave birth later than expected when treated with 20 mg/day for 3 days before rpy.

When pouch young were removed later than Day 4, birth occurred as early as 12 days after rpy.

Five of eleven animals gave birth after injection of oestradiol benzoate on Days 1 to 3 before rpy, and in three of the five the interval between rpy and birth was shorter than in non-injected animals.

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MEREDITH J. CLARK and G. B. SHARMAN

Summary.

Eight females were hysterectomized, three at 5 days, three at 10 days and two at 15 days after oestrus. Seven returned to oestrus at the expected times, 24 to 32 days after the preceding oestrus, and four of these had a subsequent oestrous cycle of normal length. The corpus luteum of hysterectomized animals killed at various stages of the first and second post-operative cycles was compared with that of control non-operated animals killed at similar stages of the cycle and no differences were found. It is concluded that hysterectomy was without effect on the ovarian cycle of the brush possum.

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G. B. SHARMAN and MEREDITH J. CLARK

Summary.

When plant growth occurred following rainfall after a period of drought in western New South Wales, Australia, 35% of a sample of sixty-five female red kangaroos were about to come into oestrus, were in oestrus or had recently been in oestrus. Only 19% of a sample taken in a comparable locality were at oestrous stages during a season of normal rainfall. After rainfall kangaroos which had failed to exhibit post-partum oestrus during the preceding drought came into oestrus and ovulated while suckling pouch young up to 163 days old. Ovulation after rainfall did not occur in kangaroos with a functional corpus luteum or a resting corpus luteum of lactation in one or other ovary. This suggests that the corpus luteum of the red kangaroo exerts an ovulation-inhibiting effect and that ovulation in this species, unlike in some other marsupials, is not inhibited by suckling. Removal of corpora lutea of lactation in suckling animals and of functional corpora lutea in non-suckling animals was followed by precocious return to oestrus. There was, however, evidence that non-suckling animals returned to oestrus following ablation of the corpus luteum sooner than did suckling animals.