Delayed return to estrus following treatment with the gonadotrophin-releasing hormone agonist, Lucrin® Depot, in the tammar wallaby

Gonadotrophin-releasing hormone agonists that induce a reversible contraceptive state in several marsupials have the potential to be used to synchronize estrus. We used a model macropod, the tammar wallaby (Notamacropus eugenii), to investigate whether Lucrin Depot (AbbVie), a GnRH agonist microsphere preparation, could (1) inhibit follicular development and estrus in a cycle reactivated by removal of pouch young (RPY) and (2) facilitate a synchronous return to estrus. Our results show that females reactivated with bromocriptine and RPY in early seasonal quiescence (July 2015) were inhibited by Lucrin Depot (0.125-0.5 mg kg −1, n = 9) and unlike control females (n = 3), did not copulate before Day 32 RPY. During the next breeding season (February 2016), the return to estrus after RPY was not delayed in animals treated with Lucrin Depot (≤0.20 mg kg −1; n = 12), and copulation occurred in treated and control females within the expected natural period after RPY (Day 26-33 RPY). In the following breeding season (March 2017), estrus was delayed in animals treated with Lucrin Depot (1.25 mg kg −1) on either Day 0 (Group A, n = 6) or Day 10 (Group B, n = 6) after RPY compared to control females (n = 6). Estrus was detected in Group A between 39 and 66 days (55 ± 4.8d) and in Group B between 43 and 71 days (55.2 ± 3.9d) after RPY. In contrast, all control females underwent estrus and copulated as expected by Day 30 RPY. We conclude Lucrin Depot can inhibit ovarian follicular activity after RPY but as a standalone treatment does not result in a highly synchronous return to estrus in the tammar wallaby.