For the past few years, the population of Przewalski’s horses in North American zoos and breeding facilities has been at risk of losing the ability to sustain itself, because many of the horses are old and past their breeding years. This means that there are not enough animals reproducing to maintain a genetically healthy population. To reinvigorate the population, National Zoo scientists have implemented an intensive captive breeding program that will increase reproduction rates through natural breeding as well as artificial reproduction techniques.
In 2007, the Zoo’s Conservation Biology Institute imported two mares from Europe to breed with one of their stallions—the most genetically valuable male in the North American population who had never sired offspring. In spring 2008, two mares imported from Europe gave birth to foals fathered by Frog.
Through research, scientists are gathering baseline knowledge about the fertility of mares and stallions within the North American herds, studying the reproductive hormone patterns of mares, and developing safe and effective methods for semen collection and cryopreservation (freezing) for artificial inseminations.
Assisted reproductive technology, such as freezing sperm and artificial insemination have great potential for increasing breeding capacity in small populations. Creating genome resource banks—frozen sperm repositories—can serve as insurance policies against unforeseen catastrophes, such as a pandemic disease. Combining the use of genome resource banks and artificial insemination could be particularly valuable in Przewalski’s horses. It could ensure reproduction between genetically valuable but behaviorally incompatible pairs, eliminating the risks associated with animal transport, and providing an avenue for infusing genes between wild (reintroduced) stocks and captive populations. Ongoing research in collaboration with The Wilds in Cumberland, Ohio focuses on improving sperm survival after thawing, understanding how well hormone therapy works on mares, and developing a standard artificial insemination protocol that consistently produces foals.
In 2008, veterinarians at the Zoo in collaboration with Sherman Silber, MD, a world-renowned urologist, performed the first successful reverse vasectomy on a Przewalski’s horse. This is the first time a procedure of its kind has been performed successfully on an endangered equid species.
The genes of Minnesota—the horse that underwent the surgery—are extremely valuable to the captive population of the species, which scientists manage through carefully planned pairings to ensure the most genetically diverse population possible. The horse was vasectomized in 1999 at a previous institution so that he could be kept with female horses without reproducing. He came to the Zoo in 2006.