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

Abstract

The contraceptive and endocrine effects of long-term treatment with implants containing the GnRH agonist deslorelin were investigated in female tammar wallabies (Macropus eugenii). Fertility was successfully inhibited for 515 6 87 days after treatment with a 5 mg deslorelin implant (n 5 7), while control animals gave birth to their first young 159 6 47 days after placebo implant administration (n 5 8). The duration of contraception was highly variable, ranging from 344 to 761 days. The strict reproductive seasonality in the tammar wallaby was maintained once the implant had expired. This inhibition of reproduction was associated with a significant reduction in basal LH concentrations and a cessation of oestrous cycles, as evidenced by low progesterone concentrations. There was evidence to suggest that some aspect of either blastocyst survival, luteal reactivation, pregnancy or birth may be affected by deslorelin treatment in some animals. These results show that long-term inhibition of fertility in the female tammar wallaby is possible using slow-release deslorelin implants. The effects of deslorelin treatment were fully reversible and there was no evidence of negative side effects. Slow-release GnRH agonist implants may represent a practicable method for reproductive management of captive and semi-wild populations of marsupials.

New insights into the reproductive physiology and management of the female koala (Phascolarctos cinereus): factors affecting the control of the oestrous cycle

“…As in eutherian species, hypothalamic secretion of GnRH from the marsupial AP regulates LH and FSH secretion (TyndaleBiscoe, 2005). Administration of GnRH antagonists has the ability to suppress LH and FSH secretion in eutherian mammals due to the competitive blockage of GnRH receptors (Herbert and Trigg, 2005) and preliminary studies in the male koala, appear to suggest a similar occurrence in marsupial species (Allen et al, 2008a). Hypothetically, administration of GnRH antagonists could be used to manipulate the female koala oestrous cycle through the temporary suppression of gonadotrophin secretion and follicular development.…”

“…The use of GnRH agonists to control reproductive function in marsupials has been largely limited to studies of contraception with positive results (Herbert et al, 2007, Herbert et al, 2004, Herbert and Trigg, 2005, Herbert et al, 2006. In light of growing interest and increased success in the use of long acting GnRH agonists and steroid implants to suppress ovarian activity in marsupials [tammar wallaby, brushtail possum (Herbert et al, 2005, Nave et al, 2000], these synthetic molecules have also recently been applied to the induction of ovulation for koala AI.…”

“…In light of growing interest and increased success in the use of long acting GnRH agonists and steroid implants to suppress ovarian activity in marsupials [tammar wallaby, brushtail possum (Herbert et al, 2005, Nave et al, 2000], these synthetic molecules have also recently been applied to the induction of ovulation for koala AI.…”

“…GnRH antagonists bind to GnRH receptors on the gonadotrophic cell membrane but don't induce stimulatory activity (Herbert and Trigg, 2005). Receptor occupancy by GnRH antagonists blocks binding of endogenous GnRH, causing an immediate suppression of gonadotropin release Crowley, 1994, Schalley, 1999).…”

“…Whilst this mechanism of action has been successfully shown to inhibit ovarian activity in marsupial species (Herbert et al, 2004a, Herbert et al, 2006, Herbert et al, 2005, the duration of agonist action is variable and reports have indicated that some individuals undergo several unsuccessful cycles before they are capable of breeding successfully after deslorelin treatment (Herbert et al, 2005). Such observations suggest that desorelin is likely to be unsuitable for the purpose of oestrous synchronization of marsupials.…”