The Latest in Breeding

What It’s All About

The impact of this new technology could be huge. Cryopreservation of oocytes—deep-freezing eggs to preserve them for future use—will give mare owners more options and give mares nearly the same reproductive flexibility as a stallion.

“[It] provides a method to preserve valuable female genetics for future generations,” says Elaine Carnevale, DVM, an assistant professor of physiology at Colorado State University (CSU) who has been working on the school’s frozen egg project, which produced those two foals in 2001. “With further development, this will allow mare owners to preserve a limited number of eggs (and potential foals) when a valuable mare dies or ages.”

And there are other benefits. Oocyte freezing also allows a performance mare to continue in competition while simultaneously launching her broodmare career years earlier than usual. However, embryo transfer provides the same opportunity, and has advantages over frozen oocytes in many cases, notes Carnevale. But, frozen oocyte breeding has the advantage when it comes to breeding mares that are poor embryo donors, she says.

In addition, oocyte freezing allows the mare owner to collect eggs from a young, fertile mare, then save them until the mare has proven herself as a performer. Even if the mare is aged and less fertile at that point—or if she dies prematurely—her eggs can still be used.

Furthermore, unlike frozen embryos, frozen oocytes aren’t fertilized until they’re placed in the recipient mare. Since only the female line is cryopreserved, you don’t pay a stud fee for the semen only to have it (or, to be precise, the embryo) sit in cold storage for an indeterminate time. And, it means that you can take your time waiting for just the right stallion to come along.

Eventually, the technology could also help preserve not only rare equine genes, but also endangered species around the globe.

How It Works

Although not yet perfected, frozen oocyte technology is definitely on its way to private breeding barns in the near future. Here’s what the process looks like:

1. Choose the donor mare. As with embryo transfer, this is the foal’s actual dam, although she likely will not carry the foal herself. Ideally, says Carnevale, the donor mare will be young—between three and 10 years of age—and healthy. “As mares get older,” she explains, “they have more problems associated with health of the eggs.” If your aim is to preserve valuable genetic material from aged mares, though, those guidelines may be ignored when the process enters the “real world” of breeding.

2. Collect the egg. Using an ultrasound probe, the veterinarian or breeding tech will gather the contents of the mare’s ovarian follicle. “We prefer to collect eggs from follicles within 12 to 16 hours before ovulation, because the success of the collection procedure is higher,” says Carnevale. “In the freezing experiment, we remove as many [eggs] as the mare has for that cycle that would be ready to ovulate.”