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The May 2022 Kaimanawa Wild Horse Muster marked the start of a new era in the management of the Kaimanawa wild horse population following the introduction of immunocontraception as a method of controlling population growth into the future.

After being researched thoroughly over the last decade, technological advancements in immuno-contraception drug efficiencies and successful overseas trials, KHH have been the driving force towards seeing this option implemented in the wild Kaimanawa herd as a complementary option to rehoming.

With musters being held annually or biannually for two decades the need to see an alternative option to help reduce rehoming requirements has long been required and the introduction of a controlled immuno-contraception strategy alongside rehoming will start to bring that change.

One of the founding aims of the Kaimanawa Heritage Horses Welfare Trust was to preserve a wild horse population with minimal intervention. However, the population growth rate of Kaimanawa Horses has meant that re-homing musters have become an annual event. This creates an enormous workload for the volunteers of Kaimanawa Heritage Horses, Department of Conservation (DOC) staff and the NZ Defence Force. Essentially up till now, horses have been allowed to breed only to be mustered and re-homed. This has always been an unsustainable method of herd management.

Since 2009 much effort has gone into looking at more sustainable and long term options to slow the rate of population growth, and eventually reduce the number of horses requiring re-homing, in addition to reducing the frequency of the musters.

Finally, in 2021, Kaimanawa Heritage Horses was able to present a strong enough case to fellow members of the Kaimanawa Wild Horse Advisory Group to see an agreement reached on the use of the immuno-contraception drug GonaCon Equine. Following the approval of the Animal Ethics Committee and installation of the necessary equipment, the first group of around 60 mares received their vaccination at the May 2022 re-homing and subsequent vaccination muster.

One of the most heart-breaking aspects of any re-homing muster is seeing family bands being broken apart to be re-homed. But finally, this year for the first time around 150 horses, comprising vaccinated mares, foals and stallions were released from the muster yards to re-form their bands and return to their home territories back in the ranges. All present agreed it was a magnificent sight and KHH Immuno-contraception Representative, Suzanne Millard, says “From my own perspective it made my 25-year involvement with Kaimanawa horses and the 13 year commitment to promoting contraception as a viable management tool worthwhile.”

Going forward rehoming musters will still be required while contraception is applied to a greater number of mares and the effects of the immuno-contraception programme become known. Monitoring of the wild herd will remain in place through aerial surveys, extensive photography programmes and ongoing data collection to ensure the correct approach can be applied in the future.

There is no intention to see a reduction in the overall herd size below the figure agreed in the management plan. All parties remain committed to seeing a healthy herd remain in the ranges while acknowledging the need for changes to future management practices so a more practicable long-term and environmentally conscience management plan can be implemented.

To see the addition of contraception as a combined tool toward maintaining a healthy and sustainable wild herd was an exciting achievement and the partnerships between KHH, DOC and the Kaimanawa Wild Horse Advisory Group will remain focused on seeing it applied throughout future years. 

GonaCon Equine – Kaimanawa Wild Horse Contraception Programme Facts

Why is contraception necessary? 

Finding suitable homes for mustered wild horses is challenging and not sustainable for long term management of the Kaimanawa wild horses.  A population management programme was developed in 1993 to keep the horse herds to a practicable level, that programme now includes the use of GonaCon Equine, a contraception drug helping reduce the wild horse population.  This initiative has been driven by the Kaimanawa Heritage Horse Welfare Society (KHH).

Is rehoming still necessary?

  • Yes.  Contraception is only one of the tools to manage population growth.  
  • Suppression of Reproduction is not permanent in treated mares.
  • The benefits of contraception will not be seen for several years.  
  • The horse population will continue to increase so rehoming is still important.  
  • Horses will still be rehomed through Kaimanawa Heritage Horse Welfare Society.

Who’s decision was it to go ahead with contraception?

The decision to implement contraception was made by the KWHAG Advisory group.  This group consists of Department of Conservation (DOC), Kaimanawa Heritage Horses (KHH), SPCA, NZ Defence Force (NZDF), Forest and Bird, equine vets and Ngati Rangi.  

What is being used?

The vaccine being used is called GonaCon Equine which administered by an intramuscular injection, suppressing reproduction in adult mares. 

Is it safe for the horses? 

GonaCon has been used as population management tool in other countries that have wild horse populations.  Findings from studies conducted have found GonaCon as a safe effective tool.  

  • Animal Ethics approval was required to undertake this work.  
  • Animal Ethics and SPCA are present during contraception programme.
  • The drug is administered by veterinarians.

How will we know if its effective in reducing population growth? 

  • The efficacy of the vaccine will be measured by the foaling rate
  • Annual aerial counts
  • Photos of each band of horses, capturing branding and makeup of band (compared year on year)
  • GonaCon Equine has been thoroughly tested over many years, and proven to be successful, in wild horses and other populations of wild mammals. 

What's next for contraception?

The challenge we now face is to ensure our future plans for seeing contraception applied as an ongoing management tool are not hindered by lack of facilities or funding.

Our extensive research on the introduction of an immuno-contraception programme also included a full analysis of the impacts to the horses. This analysis examined the various zones where the horses are located, the genetic differences throughout these areas, and the distance each group of horses would have to travel to existing facilities to be able to participate in a vaccination programme. 

With the welfare of the horses paramount in all decisions, and the need to reduce numbers in all areas while ensuring genetic variation can continue, the logical long term option is the construction of a new set of yard or yards.

When examining the distances the horses would be required to travel, we concluded that the welfare of the horses would be at risk if we attempted to take them to the existing facilities and then try to return them back to their area of the ranges.  We also looked at the environmental impact and costs associated with conducting a muster and the flying time required when mustering horses long distances. 

From a long term logistical approach it makes better sense to see the construction of new yards as the beginning of our way forward.
There is currently one set of yards constructed in the area that is available for use for any Kaimanawa wild horse-related activity. These set of yards are centrally located in what is a very vast area which means some horses are traveling up to 25 kilometers before reaching them. 

These kinds of distances usually result in many stone bruises being reported in horses mustered from these areas so the option to return them to their area cannot be considered from a welfare perspective alone. Horses being mustered from this area to the current yards will only ever have a one-way trip so the construction of another set of yards in the southern zone would help to eliminate the distance these horses would have to travel for future re-homing musters and help us ensure positive alternative management options can be extended to include these horses.

Having yards in the southern zone would allow us to continue the application of contraception to a greater number of horses which will help to reduce re-homing musters for this area more long term. Another set of yards built further north-west of the existing yards would also limit the long distances these horses also travel and further expand possibilities for the continuation of contraception in these zones.

By investing in better facilities we hope to future proof the continuation of the immuno-contraception programme as well as greatly reduce the frequency of re-homing musters for the future. It is important we apply a balanced approach to the application of contraception by ensuring mares targeted are spread throughout all areas so we can help ensure that the genetic diversity of Kaimanawa heritage horses is preserved. We know the contraception vaccination doesn’t have a lifelong effect so the need to muster horses will always remain  making better facilities an even higher priority.

Our aim now is to begin planning and fundraising for the construction of these yards that will include the facilities required to safely administer the immuno-contraception vaccination to further mares and help us reduce welfare impacts and the costs and environmental impacts associated with annual re-homing musters at such long distances.


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