Long-term fertility control in the kangaroo and the wallaby using levonorgestrel implants

Non-lethal management techniques are needed for overabundant captive and wild populations of macropodid marsupials for which lethal techniques are considered inappropriate and may be hazardous. The tammar wallaby, Macropus eugenii, was used as a model species to investigate the effect of s.c. levonorgestrel implants on reproduction during breeding and non-breeding seasons. Implants were tested on captive and wild populations of eastern grey kangaroos, Macropus giganteus. In both species, levonorgestrel successfully stopped reproduction by inhibiting oestrus. However, levonorgestrel did not affect the reactivation and subsequent development of blastocysts in diapause that had been conceived before treatment and it did not impair lactation, as young were reared to weaning in both species. The contraceptive effects of the implant were reversible, as removal of the implants from tammar wallabies was followed by a rapid return of fertility. Levonorgestrel implants had no apparent adverse effects on body condition in either species, although in the wild kangaroos a small increase in body condition did occur. Levonorgestrel implants are long-acting and so far have provided 48 months of contraception in the tammar wallaby and 27 months of contraception in the kangaroo, although the implants should provide contraception for more than 5 years in the kangaroo. Thus, levonorgestrel implants provide a safe, highly effective and long-term method of fertility control for macropodid marsupials and should be applicable for the management of overabundant captive and selected wild populations.