Long-term efficacy of levonorgestrel implants for fertility control of eastern grey kangaroos (Macropus giganteus)
Graeme Coulson A C , Christopher D. Nave A B , Geoff Shaw A and Marilyn B. Renfree AA Department of Zoology, The University of Melbourne, Vic. 3010, Australia.
B Current address: Baker Heart Research Institute, Prahran, Vic. 3181, Australia.
C Corresponding author. Email: gcoulson@unimelb.edu.au
Wildlife Research 35(6) 520-524 https://doi.org/10.1071/WR07133
Submitted: 5 September 2007 Accepted: 23 July 2008 Published: 22 October 2008
Abstract
Overabundant populations of kangaroos pose substantial management problems in small parks on the fringe of urban areas in Australia. Translocation is impractical and culling is often not publicly acceptable, but fertility control offers an acceptable alternative. One potential contraceptive is levonorgestrel, which provides effective long-term contraception in women, and prevents births in some marsupials for up to five years. We evaluated the long-term efficacy of levonorgestrel in free-ranging eastern grey kangaroos (M. giganteus) at two sites in Victoria, Australia. We trapped 25 adult females at one site (Portland Aluminium), treating 18 with two subcutaneous 70-mg levonorgestrel implants and seven with control (inert) implants. We darted 25 adult females at the other site (Woodlands Historic Park), treating all with two 70-mg levonorgestrel implants. We monitored the reproductive status of the kangaroos, as indicated by the obvious presence of a pouch young, in spring each year for up to seven years. In the first three years at Portland, 81–86% of levonorgestrel-treated females were infertile, compared with 12–29% in the control group, but the effectiveness of fertility control declined over time. At this site, the proportions of treated females breeding in the fourth, fifth, sixth and seventh years of the trial were 36%, 50%, 67% and 100% respectively. Fecundity at Woodlands was similar. Although this protocol achieved fertility control for several years, it was likely that more than one treatment or a higher dose rate would be required for effective fertility control in this long-lived species.
Acknowledgements
We are grateful to many people who assisted us at Portland Aluminium: Ruth Coulson, John Hill, Sarah Holland, Ron Jeffries, Kirstin Long, Abbie MacFarlane, Grainne Maguire, Ken O’Connor, Aldo Poiani, Dylan Salamon and Kevin Saunders, as well as our many volunteers. We are also grateful to those who helped at Woodlands: Mike Cusack, Bron Davies, Will MacAulay, Roger Martin and Fiona Smith. We thank Professor Roger Short, who made the Norplant implants available for this study, and Portland Aluminium and Parks Victoria for access to the study sites. The original project was funded by the Australian Research Council Strategic Partnership with Industry − Research and Training Scheme.
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