New insights into the reproductive physiology and management of the female koala (Phascolarctos cinereus): factors affecting the control of the oestrous cycle

Abstract

The objective of this thesis was to investigate the factors controlling the reproductive cycle of the female koala and develop an oestrous synchronization technique to facilitate the further refinement and efficacy of artificial insemination (AI) in the koala. A component of this development was the establishment of less invasive strategies to accurately monitor the reproductive status of the female koala, without the need for physical restraint or serial venipuncture. Chapter 2 of this thesis evaluated the efficacy of faecal oestrogen analysis, combined with the detection of oestrous behaviour as a control, to monitor ovarian cycles. Whilst faecal oestrogens did not correlate well with plasma oestradiol-17β to allow for an accurate estimate of cycle length or indicate or predict the precise timing of oestrus, the individual mean faecal oestrogen concentrations did, however, show a strong relationship to the individual mean plasma oestradiol-17β concentrations for each koala; in addition total faecal oestrogens were significantly higher in cycling females (P = 0.007).Chapters 3 and 4 of this thesis examined factors controlling reproductive cyclicity in the female koala. The pattern of prolactin (Prl) secretion and its relationship to oestrous behaviour and pouch young (PY) development throughout lactation in the koala was investigated in C]hapter 3.Oestrous behaviour was suppressed throughout the majority of lactation despite basal levels of Prl during early lactation. Koalas returned to oestrus some 102 days before PY had reached independence. The koala anterior pituitary also remained responsive in terms of luteinizing hormone (LH) secretion to injections of mammalian gonadotrophin-releasing hormone (mGnRH) during periods of high and low Prl secretion. Chapter 4 investigated the seasonality of oestrous behaviour (oestrous cycle activity) in a captive koala population in Southeast Queensland (SEQ).Although some individual koalas in the population showed signs of oestrous behaviour throughout the year, an obvious seasonality was apparent with significantly less females displaying oestrous iii behaviour in late autumn and winter (May -August), than September to April (P < 0.0001). While average monthly photoperiod (P < 0.0001) and average monthly temperature (P < 0.0001) were associated with oestrous behaviour, rainfall was not (P = 0.097).Chapters 5 and 6 report studies which investigated techniques, designed to allow for the manipulation and planning of timed insemination of female koalas. The impact of the gonadotrophin-releasing hormone (GnRH) antagonist, azaline B on LH and ovarian steroid hormone secretion in response to stimulation with mGnRH and its potential application in an oestrous synchronization protocol in cycling koalas was examined in chapter 5. In experiment 1, single sub-cutaneous (SC) injections of azaline B successfully blocked the ability of the anterior pituitary (AP) to respond to exogenous mGnRH in a dose dependant manner: 0 mg (n = 4) did not suppress LH response, 1 mg (n = 6) su...