Long-term effects of deslorelin implants on reproduction in the female tammar wallaby (Macropus eugenii)

Hormonal Suppression in Female Rhesus Macaques (Macaca mulatta) Implanted Subcutaneously with Deslorelin

Providing effective contraception for nonhuman primates (NHP) is challenging. Deslorelin acetate is a commercially available gonadotropin-releasing hormone (GnRH) agonist that may provide a relatively noninvasive, long-lasting, and potentially reversible alternative to standard NHP contraception methods. This study evaluated the duration of suppression of progesterone and estradiol in 6 adult female rhesus macaques (Macaca mulatta) that received a single subcutaneous 4.7 mg deslorelin implant. We hypothesized that deslorelin would suppress production of these hormones for 6 mo with a correspond- ing cessation of menses. Prior to implantation, blood was collected over 1 mo for baseline hormone analyses. Macaques were sedated at the onset of the next menstrual cycle and a 4.7 mg deslorelin implant was placed in the interscapular region. Blood was collected over the subsequent month at the same intervals used for the baseline collection schedule, and then every 7 d thereafter. Results showed that estradiol and progesterone transiently increased 1 to 3 d after implantation, then fell to basal levels within 6 d of implantation. The duration of hormone suppression (progesterone <0.5 ng/mL) varied among animals. Two macaques returned to cyclicity by 96 d and 113 d after implantation, while hormones remained suppressed in the other 4 macaques at 6 mo after implantation. Cessation of menses correlated with hormone suppression except in 1 animal that continued to have sporadic vaginal bleeding despite progesterone remaining below 0.5 ng/mL. This study indicates that deslorelin is a noninvasive and long-lasting contraceptive method in female rhesus macaques. However, individual variation should be considered when determining reimplantation intervals.

DESLORELIN (SUPRELORIN®) USE IN NORTH AMERICAN AND EUROPEAN ZOOS AND AQUARIUMS: TAXONOMIC SCOPE, DOSING, AND EFFICACY

The Association of Zoos and Aquariums Reproductive Management Center (RMC) in the US and the European Association of Zoos and Aquaria Reproductive Management Group (RMG) in Europe monitor efficacy of contraceptive products in participating institutions and use those results to inform contraceptive recommendations. This study used the joint RMC-RMG Contraception Database to analyze efficacy of deslorelin implants (Suprelorin^®), a contraceptive used in a wide range of mammalian taxa. More recently its use has increased in birds and in some reptiles and fish. Deslorelin, a gonadotropin-releasing hormone (GnRH) agonist, stimulates the reproductive system before downregulating receptors on pituitary cells that produce hormones that stimulate gonadal steroids in both males (testosterone) and females (estradiol and progesterone), interrupting sperm production and ovulation, respectively. Nevertheless, it has been used mostly in females. Efficacy has been high in mammals, with failures resulting in offspring in only 1.3% of treated individuals and 0.5% of treatment bouts. The failure rate has been higher in birds, with 14.7% of individuals in 7.2% of bouts producing eggs, perhaps reflecting differences in avian GnRH molecules. Too few reptiles and fish have been treated for meaningful analysis. Although deslorelin appears very safe, a possible exception exists in carnivores, because the stimulatory phase can result in ovulation and subsequent sustained progesterone secretion that may cause endometrial pathology. However, the stimulatory phase can be prevented by treatment with megestrol acetate for 7 d before and 7 d after implant insertion. The two current formulations of Suprelorin are effective for minimums of 6 (4.7 mg) or 12 mo (9.4 mg). The data indicate that Suprelorin is an effective and safe contraceptive option for female mammals, although it may not be effective in males of some mammalian species. Further research is needed to ascertain its usefulness in nonmammalian taxa.

Contraceptive efficacy and dose-response effects of the gonadotrophin-releasing hormone (GnRH) agonist deslorelin in Tasmanian devils (Sarcophilus harrisii)

Contraception is increasingly used to manage breeding opportunities in conservation-dependent species. This study aimed to determine the efficacy, duration of effect, optimal dose and potential side effects of Suprelorin contraceptive implants in Tasmanian devils, for use in the conservation breeding program. In our pilot study, Suprelorin was found to effectively suppress oestrous cycles in female devils, yet caused a paradoxical increase in testosterone in males. Therefore, we focussed on females in further trials. Females received one (n=5), two (n=5) or no (n=5) Suprelorin implants, with quarterly gonadotrophin-releasing hormone (GnRH) challenges used to test pituitary responsiveness over two breeding seasons. Both Suprelorin doses suppressed pituitary responsiveness for at least one breeding season, with a reduced effect in the second. There was a dose-response effect on duration rather than magnitude of effect, with high-dose devils remaining suppressed for longer than low-dose animals. There were no apparent negative effects on general health, yet captivity and contraception together may cause weight gain. Suprelorin contraceptive implants are now routinely used in the Save the Tasmanian Devil Program insurance metapopulation to meet the aims of maintaining genetic and behavioural integrity by controlling individual reproductive contributions in group housing situations.

Marsupials: Progress and Prospects

The chapter provides a review of the application of reproductive science to technologies for marsupial conservation and population management and discusses prospects for the future. This includes the status of technologies such as sperm freezing, artificial insemination, and exogenous hormone treatments to stimulate ovarian activity and cycling in the female. Fertility-based population management for introduced pest species and over-abundant native marsupials remain an elusive goal. Immune-contraceptive approaches, despite demonstration of basic effectiveness, have not progressed to field deliverable agents. Emerging genetic technologies such as gene drives offer great promise, but gene modifications face major challenges to be broadly accepted both socially and politically. A main theme is the potential advantages, both genetic and economic, of integrating frozen stored genomic material, such as sperm, into the captive breeding component of threatened species strategies. However, the sperm of many marsupial species display no or very poor recovery of motility on thawing. For this reason, it is proposed that the traditional assisted breeding paradigm for conservation-cervical artificial insemination with thawed frozen sperm, based on cattle breeding-is not a viable default strategy. Rather, techniques such as sperm injection and emerging stem cell technologies that utilize stored frozen cells, and in the case of sperm, immotile cells, are better candidates for the development of a more generic approach. In addition, this change in focus encourages wide scale proactive genome storage when genetic diversity is greatest, without the need to demonstrate success in traditional sperm cryopreservation and thawing. However, the promise of the potential of reproductive science to conservation and non-lethal population management is problematic without far greater recognition of, and investment in, the needs of wildlife by society.

Fertility Control in Wildlife: Review of Current Status, Including Novel and Future Technologies

Wildlife conservation requires varying degrees of management of endangered species as well as management of their potential predators and competitors. Conservation also depends on ameliorating human-wildlife conflict, especially where there is a threat to the safety of people and of their pets and livestock. In addition, sustainability of wildlife populations can be affected by feral domestic animals or invasive species, that require removal or control. With the increasing concern for animal welfare, non-lethal methods of limiting population size and distribution, such as fertility control, are gaining favor. Breeding programs in zoos depend on highly effective and selective contraception to manage sustainable insurance populations. This review covers fertility control methods currently in use, those that have not lived up to past promises, and others that are under development and present hope for addressing remaining challenges.

Breeding in the fat-tailed dunnart following ovarian suppression with the gonadotrophin-releasing hormone agonist Lucrin® Depot

Lucrin Depot (AbbVie), a 1-month microsphere gonadotrophin-releasing hormone (GnRH) agonist preparation, was investigated as a potential agent to synchronise cycling in the fat-tailed dunnart (Sminthopsis crassicaudata). Forty-eight randomly selected females were treated with 5 or 10mgkg-1 Lucrin Depot (n=24 per dose). Eighteen females per treatment had their reproductive activity scored at 4, 8, 12 and 16 weeks using two ovarian (Graafian follicle and corpus luteum status) and two reproductive tract (uterine and vaginal muscularity and vascularity) parameters that formed a reproductive activity score. Six females per treatment were paired with a male at 4 weeks. Fertility was assessed between 8 and 16 weeks by pouch check, and thereafter by dissection. The effects of the 5 and 10mgkg-1 doses were statistically equivalent. Females showed suppression at 4-8 weeks, an increase in reproductive activity at 8-12 weeks and all were cycling normally at 16 weeks. Six pouch young were born at 12 weeks to two females treated with the 5mgkg-1 dose. Nine embryos were recovered at 16 weeks from two females treated with the 10mgkg-1 dose. In conclusion, Lucrin Depot can suppress breeding, and fertile mating can occur in subsequent cycles in the dunnart. There is potential for Lucrin Depot to be used as an assisted breeding tool, but it may need to be combined with ovarian stimulation treatment to achieve practical levels of synchronisation in the fat-tailed dunnart.

Recent advances in tools and technologies for monitoring and controlling ovarian activity in marsupials

Components of assisted reproduction technologies (ART), such as sperm cryopreservation, artificial insemination, superovulation and pouch young surrogacy, have been developed for a range of Australian and American marsupials. However, methods to effectively control ovarian function, arguably the key limiting factors in applying and integrating ART as a practical tool in conservation management, remain poorly developed. This is largely due to unique characteristics of the marsupial corpus luteum and its failure to respond to agents used to synchronize ovarian function in eutherian mammals. This paper presents an overview of relevant aspects of marsupial reproductive biology across marsupial taxonomic groups including information on the long-established technique of removal of suckling young to activate ovarian cycles. Ovarian monitoring tools for marsupials are reviewed and their usefulness for ART assessed (laparotomy, hormone cycling, vaginal cytology, laparoscopy and ultrasonography). We also discuss promising recent work examining the potential of manipulating hypothalamic-pituitary function using GnRH agonists and antagonists as the basis of ovarian control (female synchronization) strategies.

Effects of deslorelin implants on reproduction and feeding behavior in Tasmanian devils (Sarcophilus harrisii) housed in free-range enclosures

In captive breeding programs, it is becoming increasingly important to maximize the retention of genetic diversity by managing the reproductive contribution of each individual, which can be facilitated through the use of selective contraception. This becomes critical when captive populations are held for several generations, and managers must prevent the confines of housing space and financial support from compromising genetic integrity. For example, the Tasmanian devil insurance population, established in 2006, is strategically managed to equalize founder representation. This becomes difficult when devils are housed in large groups in free-range enclosures (FREs). This study examined the efficacy, duration and potential side effects of Suprelorin^® contraceptive implants (containing 4.7 mg of deslorelin) on Tasmanian devils housed in FREs. Females were monitored to assess post-treatment reproductive rates, feeding behavior and weight changes. Suprelorin^® successfully prevented reproduction in all treated females (P < 0.001) for at least one breeding season. For one year after contraception, there was no difference in proportion of time spent feeding between contraception and control groups (P > 0.05) and there was no effect of contraception on order of arrival at food (P = 0.632), suggesting no alterations to social structure. Devils with pouch young spent more time feeding than those without (P < 0.001). Treatment and month had an interactive effect on weight (P < 0.001), yet contracepted females were only heavier than controls in one season, indicating no overall excessive weight gain. Suprelorin^® implants inhibit reproduction for at least one breeding season, with no apparent negative effects on feeding behavior or social dynamic. Selective contraception has the potential to become an important tool for conservation managers, to meet multiple reproductive, genetic and behavioral goals for this species.

Ovarian suppression in a marsupial following single treatment with a gonadotrophin-releasing hormone agonist in microspheres

The effect of treatment with Lucrin Depot (1 month), a microsphere gonadotrophin-releasing hormone agonist preparation, was investigated in the fat-tailed dunnart (Sminthopsis crassicaudata) as a potential strategy to synchronise cycling. The status of the ovaries (ovarian size, number and size of Graafian follicles and corpora lutea) and reproductive tract (weight, vascularity and muscularity) in twelve untreated females were assessed to establish the activity parameters for randomly selected cycling animals. Thirty-six females were treated with 1 mg kg–1 (n = 12), 10 mg kg–1 (n = 12) or 20 mg kg–1 (n = 12) Lucrin Depot. At 4, 6 and 8 weeks the reproductive tracts were assessed using the criteria developed in the untreated females. All of the females treated with 10 mg kg–1 showed suppression at 4 weeks and 25% showed return of reproductive activity at 8 weeks. A dose of 1 mg kg–1 did not appear to suppress reproductive activity and 20 mg kg–1 gave equivocal results, with evidence of both suppression and activity. The results indicate that Lucrin Depot appears to be a promising agent to regulate and potentially synchronise breeding activity in the fat-tailed dunnart.

Finding the Balance: Fertility Control for the Management of Fragmented Populations of a Threatened Rock-Wallaby Species

Simple Summary

Black-flanked rock-wallabies (Petrogale lateralis lateralis) can reach high numbers in fragmented populations in the West Australian wheat-belt, where they can damage crops and cause habitat degradation. As they are threatened, we wanted a non-permanent control method that did not adversely affect the body condition of treated females compared to untreated females, using body condition as an indicator of general health and fitness. We gave adult female rock-wallabies deslorelin contraceptive implants to suppress their fertility and monitored the impact for three years. Treated females did not conceive new young for over two years. We did not detect any negative effects on body condition, suggesting that deslorelin may be an effective tool for managing overabundant populations of marsupials.

Abstract

Populations of Australian marsupials can become overabundant, resulting in detrimental impacts on the environment. For example, the threatened black-flanked rock-wallaby (Petrogale lateralis lateralis) has previously been perceived as overabundant and thus ‘unwanted’ when they graze crops and cause habitat degradation. Hormonally-induced fertility control has been increasingly used to manage population size in other marsupials where alternative management options are not viable. We tested whether deslorelin, a superagonist of gonadotropin-releasing hormone (GnRH), would suppress reproduction in free-living adult female rock-wallabies without adversely impacting body condition. We trapped, synchronised reproduction and allocated female rock-wallabies to a placebo implant (control, n = 22), one (n = 22) or two (n = 20) subcutaneous implants of deslorelin. Females were then recaptured over the following 36 months to monitor reproduction, including Luteinising Hormone levels, and body condition. Following treatment, diapaused blastocysts reactivated in five females and the resulting young were carried through to weaning. No wallabies treated with deslorelin, conceivede a new young for at least 27 months. We did not observe adverse effects on body condition on treated females. We conclude that deslorelin implants are effective for the medium-term suppression of reproduction in female black-flanked rock-wallabies and for managing overabundant populations of some marsupials.

Is Wildlife Fertility Control Always Humane?

Investigation of fertility control techniques to reduce reproductive rates in wildlife populations has been the source of much research. Techniques targeting wildlife fertility have been diverse. Most research into fertility control methods has focused upon efficacy, with few studies rigorously assessing animal welfare beyond opportunistic anecdote. However, fertility control techniques represent several very different mechanisms of action (modalities), each with their own different animal welfare risks. We provide a review of the mechanisms of action for fertility control methods, and consider the role of manipulation of reproductive hormones ("endocrine suppression") for the long-term ability of animals to behave normally. We consider the potential welfare costs of animal manipulation techniques that are required to administer fertility treatments, including capture, restraint, surgery and drug delivery, and the requirement for repeated administration within the lifetime of an animal. We challenge the assumption that fertility control modalities generate similar and desirable animal welfare outcomes, and we argue that knowledge of reproductive physiology and behaviour should be more adeptly applied to wild animal management decisions. We encourage wildlife managers to carefully assess long-term behavioural risks, associated animal handling techniques, and the importance of positive welfare states when selecting fertility control methods as a means of population control.

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

The present study examined the effectiveness of the gonadotrophin-releasing hormone (GnRH) antagonist azaline B to suppress plasma LH and 17β-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 = 4) did not suppress the LH response, 1 mg azaline B (n = 6) suppressed the LH response for 24 h (P < 0.05), 3.3 mg azaline B (n = 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 = 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 = 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 17β-oestradiol concentrations and ultimately synchronise timed return to oestrus during the breeding season. Although azaline B treatment did not suppress basal LH or 17β-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.

Inhibition of the reproductive system by deslorelin in male and female pigeons (Columba livia)

Veterinary practitioners frequently encounter disorders of the reproductive system in avian patients. Management of these disorders relies on manipulating reproduction by modifying the environment, diet, and social interactions, and by the use of pharmacologic agents and surgery, with varying levels of success and side effects. An alternative is to use the gonadotropin-releasing hormone (GnRH) agonist deslorelin to suppress the pituitary-gonadal axis. To determine the efficacy of deslorelin in domestic pigeons (Columba livia), male (n = 10) and female (n = 10) birds each were implanted intramuscularly with a single long-acting implant containing 4.7 mg deslorelin. Untreated males (n = 11) and females (n = 10) were used as controls. The baseline serum concentration of luteinizing hormone (LH) was assayed at 7, 28, 56, and 84 days after treatment, and egg production was recorded weekly. In females, deslorelin administration significantly reduced serum LH concentrations compared to pretreatment levels at 7, 28, 56, and 84 days (P < .05). In males, deslorelin significantly reduced LH concentrations at 7, 28, and 56 days (P < .05). Female birds treated with deslorelin laid significantly fewer eggs over the course of the study (mean = 1.46, SEM = 0.84) compared with controls (mean = 5.54, SEM = 0.88). Deslorelin treatment had no discernible effect on body weight. Deslorelin is effective for controlling egg laying in female pigeons for at least 49 days, but further research is required to determine the effects on male fertility and the duration of action in both sexes.

Fertility control in wildlife: review of current status, including novel and future technologies

Overpopulation of selected groups of animals is widely recognised as an issue that can have adverse effects on several current global problems, such as animal and human health, conservation and environmental changes. This review will, therefore, focus on recent novel contraception together with future technologies that may provide additional contraceptive methods.

Fertility control to mitigate human–wildlife conflicts: a review

As human populations grow, conflicts with wildlife increase. Concurrently, concerns about the welfare, safety and environmental impacts of conventional lethal methods of wildlife management restrict the options available for conflict mitigation. In parallel, there is increasing interest in using fertility control to manage wildlife. The present review aimed at analysing trends in research on fertility control for wildlife, illustrating developments in fertility-control technologies and delivery methods of fertility-control agents, summarising the conclusions of empirical and theoretical studies of fertility control applied at the population level and offering criteria to guide decisions regarding the suitability of fertility control to mitigate human–wildlife conflicts. The review highlighted a growing interest in fertility control for wildlife, underpinned by increasing numbers of scientific studies. Most current practical applications of fertility control for wild mammals use injectable single-dose immunocontraceptive vaccines mainly aimed at sterilising females, although many of these vaccines are not yet commercially available. One oral avian contraceptive, nicarbazin, is commercially available in some countries. Potential new methods of remote contraceptive delivery include bacterial ghosts, virus-like particles and genetically modified transmissible and non-transmissible organisms, although none of these have yet progressed to field testing. In parallel, new species-specific delivery systems have been developed. The results of population-level studies of fertility control indicated that this approach may increase survival and affect social and spatial behaviour of treated animals, although the effects are species- and context-specific. The present studies suggested that a substantial initial effort is generally required to reduce population growth if fertility control is the sole wildlife management method. However, several empirical and field studies have demonstrated that fertility control, particularly of isolated populations, can be successfully used to limit population growth and reduce human–wildlife conflicts. In parallel, there is growing recognition of the possible synergy between fertility control and disease vaccination to optimise the maintenance of herd immunity in the management of wildlife diseases. The review provides a decision tree that can be used to determine whether fertility control should be employed to resolve specific human–wildlife conflicts. These criteria encompass public consultation, considerations about animal welfare and feasibility, evaluation of population responses, costs and sustainability.

Chronic treatment of female tammar wallabies with deslorelin implants during pouch life: effects on reproductive maturation

The present study reports on attempts to delay puberty in a model marsupial species using the gonadotrophin-releasing hormone (GnRH) agonist deslorelin. Female tammar wallaby pouch young received deslorelin (5 mg) or placebo implants (n = 8/group) when they were 193 ± 2 days old. Sexual maturity was significantly delayed in deslorelin-treated animals, with the first successful production of offspring in treated and control animals occurring at 813 ± 62 and 430 ± 42 days of age, respectively. This delay was associated with a period of retarded pouch and teat development. Progesterone concentrations remained at basal levels throughout the first breeding season, indicating the absence of luteal cycles in treated females. Recovery and maturation of the hypothalamic–pituitary axis was a gradual process. Treated animals failed to respond to GnRH challenge at 12 months of age and had a reduced LH response at 18 months of age, before attaining full responsiveness by 24 months of age. Despite this apparent pituitary recovery by 24 months of age, as evidenced by complete teat eversion and LH responsiveness to GnRH, the time to first parturition was significantly delayed beyond this time in three females. This suggests that there may be longer-lasting effects at the level of the ovary and/or on FSH secretion. The significant delay in the onset of sexual maturation in response to chronic GnRH agonist treatment in this model marsupial species may be of practical significance to the management of fertility in captive and semi-free range marsupial populations.

Brushtail possums (Trichosurus vulpecula) in metropolitan Sydney: population biology and response to Suprelorin contraceptive implants

The cohabitation of the common brushtail possum (Trichosurus vulpecula) with people in urban areas often causes conflict. Basic biological parameters are needed to evaluate potential new management options such as fertility control. This study investigated the biology of an urban brushtail possum population and the effects of Suprelorin contraceptive implants on individual females within that population. Trapping success remained constant over time, with 2.8 ± 0.2 individuals trapped per residential property. Recapture rates for males declined rapidly over time, with only 30% of males recaptured on the same property 12 months after initial capture (n = 30) and no males recaptured after 18 months (compared with female recapture rates of 58% after 18 months, n = 33). These data, combined with the preponderance of males observed within the lower age classes, suggests that male possum turnover is high within urban areas. This may be partially compensated for by the male-bias (1.8 : 1) observed in pouch young. Breeding was seasonal with the main peak of births in autumn, and a secondary smaller peak in spring. Suprelorin contraceptive treatment effectively inhibited reproduction in adult females for a minimum duration of 519 ± 7 (n = 5) and ≥700 ± 20 (n = 5) days after administration of one or two 4.7-mg implants, respectively, with no negative side-effects obvious. The concurrent collection of data on contraceptive efficacy and population-specific life-history parameters provides a unique opportunity to highlight the importance of understanding local population dynamics when evaluating the likely efficacy and implementation of fertility control programs to manage problem wildlife.

Does contraceptive treatment in wildlife result in side effects? A review of quantitative and anecdotal evidence

The efficacy of contraceptive treatments has been extensively tested, and several formulations are effective at reducing fertility in a range of species. However, these formulations should minimally impact the behavior of individuals and populations before a contraceptive is used for population manipulation, but these effects have received less attention. Potential side effects have been identified theoretically and we reviewed published studies that have investigated side effects on behavior and physiology of individuals or population-level effects, which provided mixed results. Physiological side effects were most prevalent. Most studies reported a lack of secondary effects, but were usually based on qualitative data or anecdotes. A meta-analysis on quantitative studies of side effects showed that secondary effects consistently occur across all categories and all contraceptive types. This contrasts with the qualitative studies, suggesting that anecdotal reports are insufficient to investigate secondary impacts of contraceptive treatment. We conclude that more research is needed to address fundamental questions about secondary effects of contraceptive treatment and experiments are fundamental to conclusions. In addition, researchers are missing a vital opportunity to use contraceptives as an experimental tool to test the influence of reproduction, sex and fertility on the behavior of wildlife species.

Deslorelin implants control fertility in urban brushtail possums (Trichosurus vulpecula) without negatively influencing their body-condition index

Wild brushtail possums (Trichosurus vulpecula) occur in large numbers in the grounds of Perth Zoo, Western Australia. These possums are a problem because they consume feed the zoo buys for its captive animals, damage seedlings and trees and many need to be treated for injuries sustained during fights with conspecifics. A contraceptive implant, which contains the gonadotrophin releasing hormone (GnRH) agonist deslorelin, could be a potential method of managing this population. We tested the efficacy of the implant and its impact on the body-condition index of treated possums with Kaplan–Meier analysis and a mixed model with residual maximum likelihood. We implanted 60 female possums with deslorelin and monitored reproductive success of treated and untreated possums for the following 18 months. At the conclusion of the study, 80% of 20 treated females recaptured had shown no evidence of breeding activity, giving an average minimum duration of effective contraception of 381 days. The implant did not have a negative impact on the body-condition index of treated possums during the course of the study. Our results suggest that deslorelin implants could be an effective management tool for brushtail possums at Perth Zoo and in other urban environments.

The development of a testosterone stimulation test in the Virginia opossum (Didelphis virginiana) and its use in evaluating deslorelin contraception

The aims of the present study were to examine the variability of testosterone secretion in the Virginia Opossum over a 24 h period and to develop a testosterone stimulation test that would provide an index of the prevailing testosterone biosynthetic capacity of the testes; the latter was used to clinically evaluate the efficacy of a gonadotrophin-releasing hormone agonist contraceptive. Sexually-mature captive opossums (n = 12) located in Africam Safari (Mexico) sampled every 12 h over 24 h consistently showed basal (<0.21 ng mL(-1)) blood testosterone concentrations. Intra-muscular injection of buserelin (2 microg mL(-1)) and human chorionic gonadotrophin (hCG; 1000 IU) resulted in an increase (P < 0.05) of plasma testosterone concentrations with maximal concentrations (3.9 ng mL(-1) and 5.8 ng mL(-1) respectively) occurring 120 min after injection. Plasma testosterone declined relatively rapidly to basal concentrations after 240 min with hCG but remained elevated after the same period of time with buserelin. Male opossums treated with (n = 6) and without (n = 6) a controlled-release deslorelin implant (Suprelorin; 4.7 mg deslorelin) were evaluated over a 10-week period for changes in testosterone secretion (hCG stimulation test) and sperm production (spermatorrhea). At the end of this period, the animals were hemi-castrated and their relative testicular quantitative histology compared. Testosterone concentration decreased over the course of the study in both treated and control animals (P < 0.0001) but there was no apparent effect of deslorelin on testosterone secretion, testicular histology (relative proportions of testicular cell types and seminiferous tubule diameter), or sperm production (presence of sperm in the cauda epididymis or urine).

Control of the koala (Phascolarctos cinereus) anterior pituitary-gonadal axis with analogues of GnRH

The aim of the present study was to determine whether analogues of gonadotrophin-releasing hormone (GnRH) could be used to both induce an acute testosterone response and suppress anterior pituitary function in male koalas, and induce a luteal phase in female koalas. Experiment 1 characterised the steroidogenic response of male koalas to administration of 30 μg (4.3 μg kg–1) natural-sequence GnRH. Intra-muscular injection of natural-sequence GnRH induced the release of LH and testosterone with peak concentrations at 30 min (3.7 ± 1.9 ng mL–1) and 2 h (5.4 ± 0.5 ng mL–1), respectively. In Experiment 2, a single injection of the GnRH antagonist acyline (100 μg (14.3 μg kg–1) or 500 μg (71.4 μg kg–1)) did not influence the testosterone response to subsequent injections of natural-sequence GnRH. In Experiment 3, 4 μg (~0.67 μg kg–1) of the GnRH agonist buserelin induced a luteal phase in five female koalas based on a LH surge, secretion of progestogen, and a normal-length oestrous cycle. The findings have shown that (1) natural-sequence GnRH can be used to test gonadotroph cell function and determine the testosterone-secreting capacity of male koalas, (2) the GnRH antagonist, acyline, at the dose rates used, does not suppress the pituitary-testis axis in male koalas, and (3) the GnRH agonist, buserelin, induces a normal luteal phase in female koalas.

Chronic Treatment of Male Tammar Wallabies with Deslorelin Implants During Pouch Life: Effects on Development, Puberty, and Reproduction in Adulthood1

The present study evaluated the effects of chronic GnRH agonist (deslorelin) treatment on sexual maturation in the male tammar wallaby. Slow-release deslorelin or placebo implants were administered to male pouch young (n = 10/group) when they were between 180 and 200 days old, to determine if disruption of the pituitary-testicular axis during development altered the timing of sexual maturation or had long-term effects on adult reproductive function. Deslorelin treatment caused retardation of testicular growth and reduced the serum FSH and testosterone concentrations between 12 and 24 mo of age. Maturation of the hypothalamic-pituitary-testicular axis was also delayed in treated animals at 13 and 19 mo of age. Despite these alterations in the pattern and timing of neuroendocrine development, sexual maturation was not permanently blocked in these animals and deslorelin-treated animals reached sexual maturity at the same age as treated animals, as evidenced by a fully functional pituitary-testicular axis and proven fertility at 25 mo of age. The ability of the treated animals to reach puberty at the same time as control animals, despite delayed maturation of the hypothalamic-pituitary-testicular axis, suggests that puberty in the male tammar wallaby is additionally regulated by other, gonadotropin-independent factors.

Effects of deslorelin implants on reproduction in the common brushtail possum (Trichosurus vulpecula)

The present study investigated the effects of slow-release implants containing the gonadotrophin-releasing hormone (GnRH) agonist deslorelin on reproduction in the common brushtail possum (Trichosurus vulpecula). Captive female brushtail possums were assigned to control (placebo implant), low dose (4.7 mg deslorelin) or high dose (9.4 mg deslorelin) groups; males were assigned to control or high dose (9.4 mg deslorelin) groups. The acute effects of deslorelin treatment at the level of the pituitary gland were similar between the two sexes, where a transient rise in luteinising hormone concentration was induced over the first 24 h. In females, this was associated with the disruption of the normal oestrous cycle and mating within 2–10 days in some treated individuals, but no young were subsequently detected. By 3 weeks after treatment, treated females became anoestrus and remained infertile for at least one breeding season. The effects of treatment were reversible in a subset of females that had their implants removed, although the time taken to produce offspring was variable. Paradoxically, male brushtail possums remained fertile during chronic deslorelin exposure. Despite significant declines in basal follicle-stimulating hormone and testosterone concentrations, as well as an inability to respond to a GnRH challenge, treated males sired as many offspring as control males and there was no evidence of testicular regression. In conclusion, there is potential to control reproduction in female brushtail possums by using chronic GnRH agonist treatment.

Applications of emerging technologies to the study and conservation of threatened and endangered species

Sustaining viable populations of all wildlife species requires the maintenance of habitat, as well as an understanding of the behaviour and physiology of individual species. Despite substantial efforts, there are thousands of species threatened by extinction, often because of complex factors related to politics, social and environmental conditions and economic needs. When species become critically endangered, ex situ recovery programmes that include reproductive scientists are the usual first line of defence. Despite the potential of reproductive technologies for rapidly increasing numbers in such small populations, there are few examples of success. This is not the result of a failure on the part of the technologies per se, but rather is due to a lack of knowledge about the fundamental biology of the species in question, information essential for allowing reproductive technologies to be effective in the production of offspring. In addition, modern conservation concepts correctly emphasise the importance of maintaining heterozygosity to sustain genetic vigour, thereby limiting the practical usefulness of some procedures (such as nuclear transfer). However, because of the goal of maintaining all extant gene diversity and because, inevitably, many species are (or will become) 'critically endangered', it is necessary to explore every avenue for a potential contributory role. There are many 'emerging technologies' emanating from the study of livestock and laboratory animals. We predict that a subset of these may have application to the rescue of valuable genes from individual endangered species and eventually to the genetic management of entire populations or species. The present paper reviews the potential candidate techniques and their potential value (and limitations) to the study and conservation of rare wildlife species.

Fertility control in female eastern grey kangaroos using the GnRH agonist deslorelin. 1. Effects on reproduction

Eastern grey kangaroos are widespread on the east coast of Australia and frequently reach high densities in reserves and parkland near urban areas. Management of these populations is highly contentious and non-lethal fertility-control technologies are sought as an alternative option to manage population size. This study evaluated the potential of slow-release gonadotrophin-releasing hormone agonist (deslorelin) implants to inhibit reproduction in female kangaroos. Deslorelin treatment effectively inhibited reproduction in adult females for periods of 559 ± 111 days (n = 6) and 651 ± 21 days (n = 5) after administration of one or two 10-mg implants respectively. Animals treated with the lower dosage tended to resume breeding earlier than those that received a total of 20 mg of deslorelin (minimum duration of 18 months). Deslorelin treatment had no effect on blastocyst reactivation in a single treated female and repeat treatment had no negative side-effects. This study has demonstrated that slow-release deslorelin implants can successfully inhibit reproduction for extended periods in the female eastern grey kangaroos. This approach may have potential application in reproductive management of problem kangaroo populations.