Development of Kangaroo Fertility Control

Why Research Fertility Control?

Since 1998, the ACT Government has been providing financial and in-kind support for research into methods to control kangaroo fertility. No other state or territory government has made an equal investment. Fertility control may have potential applications in certain circumstances, such as where kangaroo populations are increasing toward a damaging level but shooting would be unsafe. Fertility control is sometimes advocated by community groups opposed to lethal methods of controlling kangaroo populations.

Section 4.6.2 of the ACT Kangaroo Management Plan provides more detail about kangaroo fertility control.

Methods of Fertility Control

Fertility of eastern grey kangaroos can be successfully controlled already by methods suited to small captive populations, such as surgery, or hormone implants lasting 1–3 years. In these cases, almost every kangaroo of one sex must be handled – meaning these methods are inapplicable to most wild populations. To cause sufficient infertility to change the abundance of large free-ranging populations, it is necessary to find ways to deliver the fertility control agent in food. Population modelling suggests it is also desirable to find methods that will be effective for several years.

One promising method to cause infertility for a few years with substances deliverable in food is by vaccination (immunocontraception). Research in deer species in the USA caused infertility for at least one year by vaccinations based on either Zona Pellucida (ZP, egg coat) proteins, or the hormonal control of reproduction in the brain involving Gonadotrophin Releasing Hormone (GnRH). Both vaccine groups have been the subject of research in eastern grey kangaroos in the ACT. Both groups of vaccines (ZP and GnRH) have been tested initially in smaller marsupials more convenient to work with such as tammar wallabies (Macropus eugenii). Colonies of this small wallaby species are kept by many institutions for a wide variety of research. The primary research agencies to which ACT Parks, Conservation and Lands (PCL) has been providing support are the Marsupial Research Laboratory at the University of Newcastle, and the Invasive Animals Co-operative Research Centre (IACRC), through its partner CSIRO Entomology.

Research Approval Processes

All research involving animals must be approved in advance by legally constituted Animal Experimentation Ethics Committees, which all work to a common national Code of Practice, intended to achieve high standards of animal welfare. The committees must include members from community wildlife groups. Every year the research must be reported in detail to the committee, and every three years a new application is required. Over all the years of fertility control research, more than one ethics committee, in different research organisations, have assessed the project and been satisfied. The effectiveness of the care that is applied to kangaroos at the capture and treatment stage has been part of the assessment leading to the approvals.

Research Methods

Eastern grey kangaroos are larger than tammar wallabies (males up to 90 kg, females up to 37 kg) and have the instincts of wild animals. They are also known to be a relatively nervous, flighty species (Jackson 2003), especially prone to a range of bone fractures, and a fatal muscle condition called ‘capture myopathy’.

Elsewhere in Australia, groups of eastern grey kangaroos have been known to suffer high mortality rates even during simple capture and translocation operations (e.g. 40% mortality in the first 24 hours), which emphasises the care required by fertility control researchers., because their animals may be capture-darted multiple times over years of work.

First, dart impact force is carefully controlled, as well as accuracy. As soon as possible, the darted kangaroo is fitted with a lycra blindfold to protect its eyes and deepen the level of sedation. The blindfold is removed later by the kangaroo. Next a pad (a rolled sack) is placed beneath the shoulders to reduce the risk that the kangaroo will inhale saliva or food particles (except large-shouldered males). To help maintain the kangaroo’s body temperature in the optimum range, insulating mats, hessian bags, hot water bottles or cold water are applied as needed. In recent practice, a drug mixture is used for darting which results in more prolonged, but smoother recovery. One component of the mix can be counteracted with a ‘reversal’ drug, and this option is used if necessary to lower body temperature or speed recovery. Monitoring of the unconscious kangaroo includes temperature, heart rate, breathing rate, blood oxygen level, and capillary refill time.

More than two hundred eastern grey kangaroos have been capture-darted in this and related research, some repeatedly. A low rate of loss and injury suggests they are being handled properly. For example, 83 research kangaroos individually identified with coloured eartags or collars had been through the muster-yard-dart process carried out by Defence contractors to reduce the kangaroo population at the Belconnen Naval Transmission Station in June 2008, as well as additional research procedures. All survived the critical first month after capture, and indeed all were present six months later. During the next 12 months, three were lost due to escapes and an untreatable foot injury, leaving 80 remaining after 1.5 years. Even counting escapes as deaths, 97% survival over this time is comparatively high.

To properly understand how the experimental vaccines have worked (or not), a few of the kangaroos have to be humanely killed by lethal injection, using the same substance as used by veterinarians for pet cats and dogs, so that reproductive organs can be removed as part of the post mortem process. In addition, pouch young (mostly at an early stage - blind and hairless) have to be gently removed from the pouch at the time of vaccination, and these too are euthanased by lethal injection. Researchers acknowledge the fact that the need to humanely kill some animals makes their work unacceptable to some community groups. However other community groups support the attempts to develop non-lethal alternatives to shooting.

The latest results are awaiting completion of PhD studies before they will be released in full, but in short, none of the females treated with one of the vaccines have produced young, while every one of the control-vaccinated females has had a pouch young. This is the strongest result yet reported for fertility control medication in this species. Meanwhile, in feeding trials, a new, more attractive bait has been identified for eastern grey kangaroos.

The kangaroo fertility control research will complement other local research on kangaroo abundance, population dynamics, kangaroo home range and movements, and effects of heavy grazing on grassland biodiversity.

• Fertility Control Research - Photo Gallery

For more information about this research call Canberra Connect on 13 22 81. Also refer to other Kangaroo Research Projects being conducted in the ACT.