Making 'true' Equine IVF a Reproducible Success

By Katherine Unger Baillie 

Assisted reproduction has become an invaluable technique for horse owners hoping to pass on to another generation the characteristics of cherished and successful animals. But for decades, one of the most common methods used in assisted reproduction in humans and other animals—standard in vitro fertilization (IVF)—has been stubbornly difficult to achieve.

"It's a frustrating thing," says Katrin Hinrichs, professor of reproduction at the University of Pennsylvania School of Veterinary Medicine, who, alongside her other research programs, has tried for more than three decades to tackle conventional equine IVF, in essence, convincing a sperm to fertilize an egg in a Petri dish. "When we put horse sperm with eggs, they don't even try to penetrate them. They just swim happily about ignoring the egg, leaving us with a zero-fertilization rate."

Hinrichs and others have developed techniques to produce embryos using intracytoplasmic sperm injection (ICSI), a method of fertilization that requires the technically challenging injection of a single sperm into a single oocyte, or egg, aided by a high-power microscope and manipulation equipment. However, supporting sperm to achieve "true" IVF—in which sperm incubated in a Petri dish fertilize an oocyte without further manipulation, as they would naturally inside a mare—proved elusive.

Until now. Hinrichs and colleagues report in the journal Biology of Reproduction a major achievement in equine reproduction: a conventional IVF technique with a 90% fertilization rate, with 74% of the fertilized eggs giving rise to blastocysts, the rapidly dividing ball of cells that develops into the embryo and placenta. The three mares into which resultant embryos were transferred each carried healthy foals to term.

"The demand for assisted reproductive technologies like IVF is getting larger and larger in the horse breeding community," Hinrichs says. "The approach we've developed would allow more veterinary practices to offer IVF, as it doesn't require the expensive equipment and training needed to do it the way it's done now, by injecting each sperm into each egg. But for me the fun part is just nailing this down. I've been a horse person all my life, and for decades we have tried to figure out why this doesn't work in horses. And now we have a repeatable method that does work, so we can explore the 'why.'"