The use of a synthetic progesterone, levonorgestrel (LNG), to control the oestrous cycle in the koala.
This study investigated the efficacy of a synthetic progestogen, levonorgestrel (LNG), to control koala ovarian activity for the purposes of oestrous synchronisation. Captive koalas were administered either saline control or a 70-mg LNG implant on Day 2 of oestrus. Urogenital cytology, oestrous behaviour and plasma oestradiol-17ß and LH concentrations were monitored over a 6-week period. After LNG implant removal females were monitored to determine if the return to oestrus was synchronised. LNG-treated koalas immediately ceased displaying oestrous behaviour, showed no evidence of cornified epithelial cells in smears of urogenital cytology and exhibited low plasma oestradiol-17ß concentrations throughout the implantation period. In contrast, oestradiol-17ß levels in control koalas showed evidence of continued cyclic activity associated with behavioural oestrus and increased cornified epithelial cells in urogenital smears on Days 33 to 35 after saline injection. After implant removal, LNG-treated koalas exhibited oestrus at 13, 14, 17 and 30 days after implant removal. Plasma LH concentrations varied throughout the study period with no significant time (P = 0.49) or treatment (P = 0.13) effect. Overall results from this study suggest that LNG implants in koalas can inhibit oestrous behaviour and reduce circulating oestradiol-17ß levels before oestrus, most likely by preventing development of the pre-ovulatory follicle. However, there was no evidence of LH suppression by the LNG implants. Removal of LNG implants resulted in the synchronous return to oestrus in three of the four treated koalas. Further studies on a larger population are required to validate these findings.
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.|Corresponding author. Email: kate_068@msn.com.
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Ballantyne
School of Biomedical Sciences, University of Queensland, St Lucia, Qld 4072, Australia.
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Anderson
Currumbin Wildlife Sanctuary, Currumbin, Qld 4223, Australia.
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Pyne
Dreamworld, Dreamworld Parkway, Coomera, Qld 4209, Australia.
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Nicolson
Dreamworld, Dreamworld Parkway, Coomera, Qld 4209, Australia.
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Mucci
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.
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Lisle
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.
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Johnston
marsupial; oestrous synchronisation; phascolarctos cinereus; reproductive management