Hold your horses – brumby fertility control isn’t that easy


A government plan to ‘dart’ wild horses with fertility control drugs ignores science and expert advice. Photo: Author provided
A government plan to ‘dart’ wild horses with fertility control drugs ignores science and expert advice. Photo: Author provided

A proposed “no kill” policy for brumbies in Australia’s Kosciuszko National Park appears more compassionate, but it may ultimately and unintentionally be crueller, suggest Andrea Harvey, of the University of Technology in Sydney; Carolynne Joone, of James Cook University, and Jordan Hampton, of Murdoch University.

A proposed Kosciuszko Wild Horse Heritage Bill that rules out shooting horses is based on a flawed understanding of fertility control. Unfortunately, by ignoring scientific evidence and expert advice horses will be condemned to slow starvation.

The bill, which also proposes relocating horses within the park, or removal and domestication, intends to use fertility control for longer-term population control. But this simply isn’t feasible, and is unlikely to become so in the near future.

Vaccine darts are not a panacea

Immunocontraceptive vaccines that have been used for fertility control in wild horses in North America include the gonadotrophin releasing hormone (GnRH) vaccine, GonaCon, and porcine zona pellucida (PZP) vaccines. Administration requires injection: there is no effective oral vaccine. Injection requires either trapping horses and injecting them by hand, or darting them.

Darting brumbies requires getting very close, which is impossible in many parts of the Kosciuszko National Park. Photo: Author provided
Darting brumbies requires getting very close, which is impossible in many parts of the Kosciuszko National Park. Photo: Author provided

Immunocontraception has been successfully used only in smaller and more isolated populations (such as islands). Population modelling has estimated that more than 50% of mares would need to be treated in Kosciuszko National Park (KNP) just to slow the rate of population increase within 2–5 years.

Although the precise number of horses in KNP is hotly debated, even at the lowest estimates almost 1,000 mares would need to be treated to have the desired impact on population growth – and it would still take 10–20 years before the population size was reduced substantially through natural mortality. And that is on the proviso that we could actually administer the vaccine to this number of mares.

Trapping enough horses across KNP (an area of about 700,000 hectares) would likely be impossible. Dart administration sounds intuitively appealing but is a complex process and will not be possible for large numbers of horses in difficult, mountainous terrain.

Staff must be extensively trained for licences before they can administer darts. More importantly, darting can only be safely performed within around 40 metres of a stationary horse, and with a clear line of vision. This must be done accurately and without causing ballistic injuries.

Injected animals must be marked (with dye, for example) so that they can be identified for booster shots as needed.

As demonstrated in a recent trial of fertility control darting for eastern grey kangaroos in the ACT, it is extremely challenging to manage all of these goals in the field. Helicopters can be used to dart animals, but this adds animal welfare impacts due to pursuit and lower levels of accuracy.

In other parts of the world where dart administration of immunocontraceptives has been successful, they have been applied to horses that are used to people, allowing staff to approach horses on foot. This is a very different situation to KNP.

Although it is possible to closely approach some horses in KNP, ongoing research has revealed that it is only possible to get within 200–500m of most horses in the larger populations.

Furthermore, it would be close to impossible to both identify and locate the same horses on multiple occasions, as required for booster vaccination injections. In more densely forested areas, it can be challenging to even see horses, let alone dart them.

There is no vehicle access to many parts of KNP where horses live, and long treks across challenging terrain would make attempts to locate all horses very labour-intensive. Furthermore, many areas of KNP are completely inaccessible in winter because of to snow, making darting before the spring breeding season even more problematic.

What would we be vaccinating horses with?

There’s also the question of what exactly the horses would be vaccinated with. GonaCon and PZP are not produced in commercial quantities, are not currently available in Australia and are not straightforward to import. Australian quarantine regulations may prevent the import of reagents derived from animals, such as conventional PZP which is derived from pig ovaries.

Producing PZP in Australia brings additional challenges, without guaranteeing the same efficacy. While work on a synthetic PZP formulation is ongoing, initial results in mares were disappointing.

There are two alternative GnRH vaccines available in Australia. One has shown less effectiveness than required in a pilot trial and while the other is registered for use in domestic mares, it lasts a relatively short time and is prohibitively expensive.

Most contraceptive vaccines require an initial injection followed by a second injection about one month later to achieve maximum efficacy, and then annual booster injections. GonaCon is promoted as having 3-year efficacy after a single injection, but that significantly reduces after the first 12 months. Long-acting PZP formulations have been investigated in North America; while results appeared promising initially, more recent work showed a contraceptive efficacy of under 60% beyond one year after treatment. Furthermore, the viscous nature of these longer-acting formulations make administration by dart more challenging.

Alternative fertility control options such as surgical sterilisation or intra-uterine devices have even more practical hurdles. For all of these reasons, a recent peer-reviewed study by two Australian reproductive experts concluded that current fertility control methods are not feasible for halting the population growth of wild horses in Australia.

Although some newer technologies are undergoing investigation, realistically it will be a long time before contraception for wild horses becomes an effective reality in Australia.

‘No kill’ means slow starvation

Without a feasible method for sterilising horses, the newly proposed bill will mean population control is mainly through food limitation.

While “no kill” is seemingly more compassionate, it may ultimately and unintentionally be crueller.

As horse populations reach the carrying capacity of their habitats, they become malnourished and their fertility declines. Horses in very poor condition will not produce foals. When malnutrition persists, many horses will die young and many will die slowly.

This was dramatically demonstrated four years ago, when researchers discovered emaciated brumbies in the Snowy Mountains cannibalising their fellows and more emerging research is further confirming that extreme malnutrition is ongoing in parts of KNP.

The ConversationIn time, the number of horses suffering chronic malnutrition and dying of starvation is likely to increase. Is this truly humane population control?

Andrea Harvey, Veterinary Specialist, PhD scholar (wild horse ecology & welfare), University of Technology Sydney; Carolynne Joone, James Cook University, and Jordan Hampton, Adjunct Lecturer, Murdoch University.

Read more:
NSW’s no-cull brumby bill will consign feral horses to an even crueller fate
This article was originally published on The Conversation. Read the original article.

It is published under a Creative Commons License.

One thought on “Hold your horses – brumby fertility control isn’t that easy

  • June 3, 2018 at 4:24 am

    While I appreciate the valuable professional information which this article provides, I believe that it commits a serious error in jumping to conclusions concerning the arbitrary assertion that naturally living horses will inevitably overpopulate, ruin their habitat, and then consequently starve to death. The authors assume that the horses will merely continue to reproduce and that no limiting factors other than starvation will come into play. The article shows a few pictures of thin brumbies that are expected, I suppose, to sway readers into a reactionary mode and get them on board for the brumby shooting option that has been proposed. This lopsided approach is very tendentious and overlooks the brumbies’ greater history as well as role in the natural world.

    Back in October 2014 I travelled to Australia and visited several brumby-containing ecosystems throughout this marvellous country and continent, including the Snowy River and Kosciuszko National Park region, where I was guided both by brumby defenders and by park biologists. The vast majority of the brumbies I saw — and I saw 100’s all totaled — were in excellent condition and I did not notice any extreme degradation of the ecosystems in question. There were some disturbances around certain areas where the horses came into drink, but not excessive. And there were Corroboree frogs nesting here that did not seem to be overly affected.

    I presented a poster at the annual conference of the Ecological Society of Australia when I was here and highlighted the many ecological services that naturally living horses contribute, one of the chief of which is catastrophic wildfire prevention. And this is something that Australia should be particularly keen about given its increasing wildfires that are being exacerbated by Global Warming. And the same observation applies here in the western U.S. as well as in many other places.

    Before closing, I would like to remind the reader that I am in favor of preserving the unique species of animals and plants that have evolved over many millions of years in relative isolation upon the unique and amazing Australian continent. Measures should be taken to preserve these wherever possible. But since 1788 when the first European colonization began, there have been immense changes introduced into this ecosystem, many concern the promotion of cattle and sheep raising and other agricultural interventions. As in so many other parts of the world, horses were one of the mainstays of this colonization. But with the advent of tractors and automobiles, the horses found themselves displaced. Some escaped to freedom and following their age-old instincts sought to survive and to perpetuate their kind, as do we humans as well, by the way.

    Somehow it strikes me as uncharitable in the extreme to treat these highly evolved, sensitive and intelligent, basically generous and good-willed beings in horse form, who have done so much for us, as mere objects to be discarded. We humans have a natural affinity with these highly evolved presences, and they deserve our just respect and consideration. They should not become mere targets, blamed for all kinds of things simply because they are large and attention-attracting animals. They should not be set up for a cruel and heartless elimination program that is intellectually biased because it fails to consider the horses as well as Life’s greater past history, interrelated community, and evolving future.

    I would be glad to allow for the publication of my poster on the brumbies, which, in addition to illustrations, contains a written list of positive points about these animals that apply in many places, including in Australia. One of the chief of these concerns the fact that horses are not Ruminant-digesting herbivores like most of the herbivores promoted by modern society such as cattle, sheep and deer, but rather equids are Post-gastric-digesting herbivores. This is a major consideration and substantiates the horses’ greater contribution to the greatly enriching humus content of soils, and to their dispersing of more intact seeds and of a greater variety of species in intact condition and capable of germinating. This can greatly help many of Australia’s native plants and animals as adjustments between all these species evolve naturally, not just according to some narrow-minded and hard-hearted preconception of what species belong and what don’t. It is my hypothesis that the brumbies have much more that is positive to contribute to Australia than negative, that they are restorers of balance in many of the vast areas such as the Outback that have been overwhelmed by Ruminant herbivores brought in by modern man. And by the way, they do have natural predators here, such as the Dingos as well as such animals along the coasts and river inlets as Salt Water Crocodiles. I believe that we should let Nature show us what the New Harmony in the Life Community can become. We humans should pull in our horns and learn to appreciate the Whole of Life from a Higher Plane of Understanding, one that is much more spiritual in its recognition of that great transcendent Essence that all conscious beings not only Share, but ARE!


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