A pilot project in Alberta is using birth control vaccinations to help control the wild horse population.

So far, 73 mares have been injected with Zona Stat-H, also known as PZP, a vaccine that helps to prevent fertilization with up to 90 per cent effectiveness.

The effects of the contraceptive are reversible, can be delivered remotely using small darts and will not harm the fetus if a pregnant animal is vaccinated.

Only use on an individual for five or more consecutive years will risk sterility.

The project is part of a five-year agreement signed between the Alberta government and the Wild Horses of Alberta Society in November 2014.

The PZP vaccine is administered to feral horses like these by remote darting. (WHOAS/Facebook)

'Most humane' solution

"It's the most humane and a very effective method of controlling the numbers," said Bob Henderson, president of WHOAS.

Henderson said his organization was motivated to find a better solution after being able to save just nine of more than 200 wild horses that were captured in 2012. Most of the remaining feral horses were destroyed, he said.

The PZP vaccine is "used extensively" in the United States, particularly in Nevada and Wyoming, Henderson said.

The province's most recent estimates count 851 wild horses in the Foothills area, compared to 880 in April 2014.

The birth control project is being piloted in a 490-square-kilometre area of Sundre to test its effectiveness on slowing population growth.

Depending on the study's success, contraceptives could be considered for other equine zones.