Effect of deslorelin implants on follicular development, parturition and post-partum oestrus in the tammar wallaby (Macropus eugenii)

Abstract

The effect of treatment with slow release implants containing the GnRH agonist, deslorelin, was investigated in female tammar wallabies. Pouch young were removed from 16 wallabies presumed to be carrying quiescent blastocysts. Eight received a 5 mg deslorelin implant and eight received a placebo implant. Animals were caught daily from day 25 to day 30 and their pouches inspected for newborn young and their urogenital sinus checked for a copulatory plug. Treatment with deslorelin did not affect reactivation of a dormant blastocyst and subsequent birth in 4/8 animals, but post-partum mating was inhibited in these animals. Five control and five treated animals were killed within 0-48 h post partum and their reproductive tracts analysed. At autopsy, all five control animals had large preovulatory follicles but only one deslorelin-treated animal showed signs of follicular development. These differences were also reflected in the weights of the lateral vaginae, with treated animals showing no evidence of oestrogenic stimulation. The remaining three control and three treated animals were monitored for approximately 2 years. The long-term contraceptive effects of a single 5 mg deslorelin implant lasted for just under one year. These results indicate that slow release deslorelin implants inhibit follicular development in the female tammar wallaby for extended periods of time and may have potential application in reproductive management of captive marsupials in the kangaroo family.

Long-term effects of deslorelin implants on reproduction in the female tammar wallaby (Macropus eugenii)

“…This is supported by previous observations that treatment with deslorelin inhibited follicular development and oestrus in the female tammar (Herbert et al 2004a). During deslorelin treatment progesterone concentrations were only slightly higher than those measured in two ovariectomised animals.…”

“…In six out of seven animals there was no evidence of successful reproduction for at least 344 days after implant administration. This minimum duration of contraception was very similar to the duration of 340 and 359 days previously recorded for two animals in a smaller trial (Herbert et al 2004a). Inhibition of reproductive activity in the current study was associated with a reduction in peripheral plasma LH and progesterone concentrations.…”

“…The in vivo release rate in tammar wallabies has not been determined. This dose was previously found to be effective at suppressing post-partum mating and follicular development in tammar wallabies (Herbert et al 2004a). Implants were placed s.c. between the shoulder blades using a single-use commercial implanting device sterilised by e-beam radiation.…”

“…The iconic status of these animals often places sociopolitical constraints on management options, with lethal methods facing increasing opposition (Adderton Herbert 2004). This has resulted in research and development of new techniques to manage populations by reducing their fertility (fertility control), such as the use of synthetic progestins (Nave et al 2000, Middleton et al 2003 and gonadotrophin-releasing hormone (GnRH) agonists (Herbert et al 2004a).…”

“…Despite the variable effects on basal LH, the preovulatory LH surge appears to be universally inhibited, as is ovulation. Preliminary trials on a model macropodid species, the tammar wallaby (Macropus eugenii), have demonstrated that implants containing the GnRH agonist deslorelin inhibit follicular development and post-partum oestrus (Herbert et al 2004a). The next phase of the investigation is to study the long-term effects on reproductive success and endocrine parameters.…”