A pioneering project to put Dartmoor's wild ponies on the pill is to begin in Devon later this year.

Concerns has been growing for several years about overbreeding among the semi-feral animals, high numbers of which have ended up in horse sanctuaries or slaughtered and the meat sold overseas as their market value has plummeted.

The recession has further affected sales of the ponies, with fewer people prepared to take on and train up a half-wild animal, despite their temperaments and intelligence making them ideal as children's riding ponies.

Now vets working for World Horse Welfare have been given the go-ahead to bring in injection from Australia to control the numbers of foals being born on the moor.

WHW veterinary consultant Keith Meldrum has been working closely with the Dartmoor Hill Pony Association (DHPA) and the pharmaceutical company Pfizer on proposed plans to provide a group of 20 mares with a contraceptive injection.

"A project of this kind has never been carried out before in the UK and I am delighted to be a part of it," he said. "We are hoping that, if successful, this could become a long-term solution to the issue of overbreeding within Britain's semi-feral horse and pony populations."

Meldrum said the treatment was not as invasive as sterilising the mares.

"We feel that this method of control is advantageous as the mares can come back into foal after the treatment; its simply means there is simply a reduction in foal production for the duration of the project. We are close to starting the initial injections now that we have the [drug] in our possession and after the Veterinary Medicines Directorate gave us the go ahead for batches to be imported from Australia into the UK."

There are thought to be fewer than 1,000 of the ponies left on the moor, down from an estimated 25,000 in the 1930s. In late spring a team led by Meldrum plan to round up ponies into a holding area where they will be micro-chipped and marked in a way in which they are identifiable at a distance. They will then be given an injection, and four weeks later given a second dose.

After a six-month period the mares will be blood-tested to see if their oestrus levels have been suppressed owing to the injection. If the mares respond positively after the initial six months, then they will receive a further does which will last until spring 2013.

The secretary of the DHPA, Charlotte Faulkner said: 'The adult pony numbers on the moor need to be maintained at its present number for the benefit of Dartmoor, but the number of foals need to be reduced as there is no market for them at the moment.

"Controlling the production of unwanted foals will ensure the ponies' welfare. We are optimistic that this project will help us to ensure the future of ponies on Dartmoor, grazing to keep it as we know and love it for generations to come, creating the habitat for its wonderful birds, plants and animals to be conserved."

The project is being sponsored by Friends of the Dartmoor Hill Pony.