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

Abstract

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.