Summary. Pouch young of wallabies presumed to be carrying diapausing blastocysts were removed from the teat for times varying between 24 and 96 h and then returned to the same teat. The mothers were monitored for termination of diapause and checked for births or oestrus. In this way we were able to determine the critical time required to reactivate the quiescent corpus luteum and diapausing blastocyst after withdrawal of the sucking stimulus. When pouch young were removed from the teat for 76–96 h the corpus luteum and blastocyst were reactivated, with birth and/or oestrus occurring in 10/11 animals. When pouch young were removed for 72 h or less (n = 22) reactivation did not take place.
We conclude that it takes longer than 72 h for the maternal endocrine system to become committed to reactivation. The precise sequence of endocrine events which precede blastocyst reactivation still remains to be determined.
Keywords: corpus luteum; sucking; tammar; diapause; blastocyst
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