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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