Frozen eggs yield first foals at CSU lab

Aug 01, 2001
By staff

Fort Collins, Colo.-The first-ever foals produced from eggs harvested from a mare, frozen and then thawed, were born in mid-July at Colorado State University's Animal Reproduction and Biotechnology Laboratory.

Scientists say they will now be able to preserve reproductive material from the female and the male. The technology may help to preserve endangered species worldwide, which has been a goal of CSU's Preservation of Equine Genetics program since its inception in 1996.

"This is a tremendous breakthrough," says Dr. Ed Squires, faculty member and coordinator of the Preservation of Equine Genetics program. "Essentially, with this process, we can now do for the female mammal what we've been able to do for the male: provide flexibility in reproduction."

In comparison to the stallion, which can produce millions of sperm for many years, mares have a limited number of eggs, or oocytes, and fewer years for reproduction. Typically, mares are bred for the first time at around 3 years of age and deliver between eight and 10 foals in a lifetime.

Because the oocyte cell is so much more complex than a sperm cell, the process of cryopreservation is much more tedious.

"The cryopreservation process we used in this case is called vitrification," says Lisa Maclellan, coordinator of the project. "We first gathered the contents of an ovarian follicle using an ultrasound probe. From the contents, we separated out the single-cell oocyte under a microscope. The oocyte was placed onto a cryoloop-which is about the size of a sewing needle--and quickly dipped into liquid nitrogen to be flash frozen."

The oocytes were thawed after several months and implanted in two mares that had already been inseminated with material from a donor stallion. The mares carried for the full term and delivered healthy, normal foals.