CSIRO PUBLISHING www.publish.csiro.au/journals/rfd Reproduction, Fertility and Development, 2007, 19, 335–340 Effects of levonorgestrel on ovulation and oestrous behaviour in the female tammar wallaby Emily F. Hynes A,C , Chris D. Nave A,B , Geoff Shaw A and Marilyn B. Renfree A A Department of Zoology, The University of Melbourne,Vic. 3010, Australia. B Present address: The Baker Heart Research Institute, Vic. 3181, Australia. C Corresponding author. Email: e.hynes@pgrad.unimelb.edu.au Abstract. Subcutaneous hormone implants are a useful method for managing overabundant marsupials in restricted enclosures in Australia. Levonorgestrel induces long-term infertility in the kangaroo, tammar wallaby and koala, although the contraceptive mechanism of levonorgestrel is unknown for any marsupial. In the present study, it was investigated if insertion of a single levonorgestrel or control implant at the time of reactivation of the diapausing blastocyst affected the subsequent post-partum oestrus or the preceding follicular development.Twenty levonorgestrel-treated and 16 control animals were autopsied the day before birth and the accompanying post-partum oestrus (Day 25), and 10 levonorgestrel- treated and five of the nine control animals were autopsied 3–4 days (Days 29–30) after the expected birth and oestrus. Peripartum behaviour was observed and birth and mating times were recorded. Levonorgestrel treatment did not prevent follicular growth because there was no significant difference between treatment and control animals in the size of the dominant follicle at Day 25. None of the levonorgestrel-treated females autopsied at Days 29–30 had ovulated (n = 10), in contrast to controls, where four of the five that were autopsied had ovulated. Mating occurred in eight of nine control animals but in only three of 10 levonorgestrel-treated females. Males showed a more sustained period of interest in the three that were mated than in the controls, and mating took place significantly later after birth (36 v. 10 h; P = 0.038). Follicular growth and development was not blocked in any female but only one-third of the animals mated and none ovulated after levonorgestrel treatment. These results suggest that levonorgestrel inhibits the preovulatory surge of luteinising hormone. Additional keywords: contraception, follicular development, gestagen, Macropus eugenii, marsupial. Introduction Levonorgestrel implants are effective contraceptives in mam- mals, including marsupials. The mechanism of action has not been previously studied in marsupials but may differ between species and it is important to determine whether the contracep- tive induces undesirable effects, such as constant oestrus, before wide application to wild species. In women, levonorgestrel inhibits follicular maturation and ovulation by decreasing the release of follicle stimulating hor- mone (FSH) and blocking the preovulatory surge of luteinising hormone (LH) (Alvarez et al. 1986; Segal et al. 1991). The dis- ruption of the endocrine profile causes a variety of dysfunctions that range from anovulation to an insufficient luteal phase (Segal et al. 1991). Ovulation sometimes occurs but is associated with an abnormal endocrine profile (Alvarez et al. 1986). The per- turbation of the periovulatory endocrine profile has secondary contraceptive effects, including the reduction of cervical mucus secretions and increased viscosity, thus preventing the migration of spermatozoa through the cervical canal (Brache et al. 1985; Segal et al. 1991). In two primate species, the white-faced saki and the chim- panzee, levonorgestrel causes infertility in essentially the same way as in women (Bettinger et al. 1997; Savage et al. 2002). Domestic cats are induced ovulators and when treated with lev- onorgestrel, follicular recruitment and oestrus is suppressed and progesterone concentrations remain basal, indicating anovula- tion or defective luteal function (Baldwin et al. 1994). Levonorgestrel implants also cause infertility in marsupials that lasts for 3–5 years in tammar wallabies and eastern grey kangaroos and at least 6 years in koalas (Nave et al. 2000, 2002; Middleton et al. 2003). However, the contraceptive mechanism by which levonorgestrel prevents pregnancy in these marsupials is unknown. The tammar is monovular, and polyoestrus, with ovulation occurring in alternate ovaries in each cycle (Tyndale-Biscoe and Renfree 1987). Females have an immediate post-partum oestrus and ovulate 40–50 h later (Sutherland et al. 1980; Harder et al. 1985; Rudd 1994; Renfree and Lewis 1996). The resulting con- ceptus grows to a 100-cell unilaminar blastocyst before entering lactational diapause (Tyndale-Biscoe and Renfree 1987). Loss or removal of the pouch young (RPY) during this period removes the prolactin inhibition of the corpus luteum (CL), resulting in resumed progesterone synthesis and blastocyst reactivation (Hinds and Tyndale Biscoe 1982; Shaw and Renfree 1984). Birth occurs around 26 to 27 days later and undisturbed females mate 1.3 ± 0.8h post-partum (Rudd 1994). However, handling © CSIRO 2007 10.1071/RD06063 1031-3613/07/020335