Use of the gonadotrophin-releasing hormone antagonist azaline B to control the oestrous cycle in the koala (Phascolarctos cinereus)

K. BallantyneA,E, S. T. AndersonB, M. PyneC, V. NicolsonD, A. MucciD, A. LisleA and S. D. JohnstonA

ASchool of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.
BSchool of Biomedical Sciences, University of Queensland, St Lucia, Qld 4072, Australia.
CCurrumbin Wildlife Sanctuary, 28 Tomewin Street, Currumbin, Qld 4223, Australia.
DDreamworld, Dreamworld Parkway, Coomera, Qld 4209, Australia.
ECorresponding author. Email:

The present study examined the effectiveness of the gonadotrophin-releasing hormone (GnRH) antagonist azaline B to suppress plasma LH and 17b-oestradiol concentrations in koalas and its potential application for oestrous
synchronisation. In Experiment 1, single subcutaneous injections of azaline B successfully blocked the LH response to exogenous mammalian (m) GnRH in a dose-dependent manner; specifically, 0 mg (n ¼ 4) did not suppress the LH response, 1 mg azaline B (n ¼ 6) suppressed the LH response for 24 h (P , 0.05), 3.3 mg azaline B (n ¼ 8) suppressed the LH response significantly in all animals only for 3 h (P , 0.05), although in half the animals LH remained suppressed for up to 3 days, and 10 mg azaline B (n ¼ 4) suppressed the LH response for 7 days (P , 0.05). In Experiment 2, daily 1 mg, s.c., injections of azaline B over a 10-day period during seasonal anoestrus (June–July; n ¼ 6) suppressed (P , 0.01) the LH response to mGnRH consecutively over the 10-day treatment period and, 4 days after cessation of treatment, the LH response had not recovered. Experiment 3 was designed to test the efficacy of daily 1 mg, s.c., azaline B over 10 days to suppress plasma LH and 17b-oestradiol concentrations and ultimately synchronise timed return to oestrus during the breeding season. Although azaline B treatment did not suppress basal LH or 17b-oestradiol, oestrus was delayed in all treated females by 24.2 days, but with high variability (range 9–39 days). Overall, the present study demonstrates that the GnRH antagonist azaline B is able to inhibit the LH response in koalas to exogenous mGnRH and successfully delay the return to oestrus. However, although azaline B clearly disrupts folliculogenesis, it has not been able to effectively synchronise return to oestrus in the koala.