Feral horse populations can be difficult to manage, but a new intrauterine device (IUD) that puts itself together with magnets inside the uterus could help sterilise mares and solve overpopulation issues.
Current feral horse sterilisation techniques are impractical because they require darting each mare with contraceptive chemicals every year after an initial injection and five-week booster. “When you’re talking about hundreds of thousands of animals across a vast territory, keeping track of each individual mare’s schedule is just impossible,” says Carolynne Joonè at James Cook University in Australia.
Joonè and her colleagues tested an IUD made of three polymer-covered magnetised parts that “find each other” and connect into a ring shape. Each part is 4 centimetres long and 1.6 centimetres wide, so they can be inserted without dilating the horse’s cervix, but the final ring shape is large enough that the IUD won’t fall out.
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That means they could prevent pregnancies in a horse for years, she says. To place them in feral horses, the mares would need to be captured and secured for the few minutes necessary to insert the parts through the cervix. But that’s still better than darting year after year, especially since horses are such “quick learners”, she says. “Their avoidance behaviour gets worse with time.”
To see if this method could prevent pregnancies in feral horses, Joonè and her collaborators tested it in 14 university-owned female horses of a racing breed. They placed the IUD parts in seven of the mares, and artificially inseminated all 14 with sperm from the same fertile stallion. The IUD correctly assembled itself in all seven treated mares, and none of those horses became pregnant, while all seven of the mares without the IUD did. The horses had no major side effects from the IUD.
“If it works like this in the brumbies [Australian feral horses], that would be great,” Joonè says. “It’s an option, and we need options at this stage.”
Native to neither Australia nor the US, free-roaming horses in both countries descended from imported domesticated horses hundreds of years ago and have since created significant population management challenges. Mares usually produce one foal per year, leading to an estimated annual population growth of 20 per cent. In large numbers, they can deplete natural resources and create road hazards. Government-led management techniques like sniper-shooting from helicopters in Australia and chasing the horses by helicopter into holding pens in the US have incited strong public criticism.
The IUD might provide a better answer, says Joonè. “It’s not going to be the answer for everything, but it might be part of the solution,” she says.
Australian Veterinary Journal
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