URUMQI - Summer is the best season for those living on the grassland in a semidesert area in Urumqi, Xinjiang Uygur autonomous region, but for 25 mares it has been tough for the past three years.

They are Przewalski's horses, native to the steppes of Central Asia and considered the only true wild horse in existence today.

Once extinct in China, they were successfully reintroduced to the country in the 1980s from Europe, yet are still on the brink of extinction as mating has become a big challenge in their conservation.

Summer is their mating season, but the 25 female Przewalski's horses have failed to find a mate over the past three years.

"The 25 mares share too close a genetic relationship with the stallions at our center and therefore they cannot copulate," said Zhang Hefan, a senior engineer at the Xinjiang Wild Horse Breeding and Research Center, the largest wild horse breeding base in Asia.

"Increasing their number is not enough to protect these wild horses, we must avoid inbreeding and enrich their genetic diversity through gene exchange," Zhang said.

Since 1986, a total of 24 Przewalski's horses have come from Britain, Germany and the United States to mate with their local partners. Many of their offspring have returned to nature, which significantly helped the conservation of the rare horses.

As the number of Przewalski's horses has registered a steady increase in Xinjiang in recent years, Xinjiang also transported four stallions to Mongolia in 2012 as part of international cooperation on conservation of the species.

To help the 25 wild horses find suitable male partners, the center has been contacting zoos across the globe.

But an international marriage has never been easy. Two years ago, a zoo in Prague intended to send six stallions to Xinjiang, but it ended in vain as China and the Czech Republic had no protocol on the quarantine and transportation of horses.

"Many governments and people from nonprofit organizations are trying hard to search for suitable mates for these female horses," Zhang said. "We hope they can find their partners in the near future."

Xinhua