Researchers successfully make horse embryo with IVF, a first in Florida

The performance horse industry had a problem: Some of their most beloved and sought-after mares simply couldn’t have foals safely. To make matters more complicated, in-vitro fertilization (IVF) had not yet produced a healthy equine embryo, despite years of success in other species like cattle.  
 
But in a significant step forward for the industry, University of Florida Department of Animal Sciences researchers recently announced they were finally able to successfully fertilize an equine egg using IVF, the first time this feat has been accomplished in the state of Florida.  
 
The Florida horse industry is a significant economic driver, with breeding, training, show events, racing, rodeo and polo supporting an estimated 244,200 jobs and an annual economic impact of $6.8 billion, with indirect impacts like equine tourism contributing an additional $11.7 billion, according to the Florida Department of Agriculture and Consumer Services. 

This discovery has resounding implications for the performance horse industry, which prefers to choose talented and highly valued mares to have the next generation of foals but need those mares to do so safely and in a way that keeps them healthy. The study was published online in Reproductive Biology and scheduled for print publication in June. 
 
Some mares cannot successfully conceive or carry their own pregnancies. This can be due to foaling trauma, uterine diseases or other complications such as limping that would be an additional burden under the weight of a pregnancy, all of which can threaten the mare’s health.   

For those reasons, placing the embryo inside a surrogate may be a safer alternative for both the mare and the embryo. But first, researchers needed to figure out the crucial step of making an equine embryo possible with IVF, and it starts with figuring out the secrets of horse sperm.  

“There are lots of scenarios where it might be unsafe or unwise for a mare to carry her own foal, so IVF would be a useful tool,” said study author and UF Institute of Food and Agricultural Sciences (UF/IFAS) Department of Animal Sciences assistant professor Brad Daigneault. 

Equine sperm doesn’t behave like cattle or human sperm when it comes to IVF, Daigneault said. Stallion sperm need to undergo physical and biochemical changes first, called capacitation, which in the case of equine IVF, require a unique temperature within a specific timeframe before sperm are capable of breaking through into a mare’s egg.  

UF/IFAS researchers experimented with chilled sperm – which is the industry standard for artificial insemination – as well as fresh sperm and frozen-thawed sperm at various temperatures for different lengths of time. They found that while chilled sperm is the most-used method for many in the equine industry, frozen sperm that had been thawed worked much better. 

“Instead of using fresh or cooled sperm, which would intuitively seem more successful for IVF than frozen sperm, the data told us that frozen-thawed sperm might actually be more effective,” Daigneault said.  

Using frozen sperm has several advantages over chilled or cooled sperm because it can be stored indefinitely and then thawed when eggs from the mare are available. This approach is convenient for producing embryos and is more user-friendly than chilled sperm that requires shipment and typically survives for a day or two. By innovating the practice of IVF using frozen sperm, horse owners, veterinarians and technicians will be able to plan accordingly at a time that is right for them, he said. 

 Since the freezing and thawing process puts mild stress on the sperm, that biological pressure actually caused the changes necessary for capacitation, meaning frozen sperm could be used immediately after thawing and with fewer steps, Daigneault said. 

IVF involves exposing unfertilized eggs to sperm and allowing the sperm to penetrate the eggs unassisted. Intracytoplasmic sperm injection, or ICSI, is a separate technique in which a single sperm is injected directly into the cytoplasm of the egg, thereby bypassing requirements for sperm fusion and sperm penetration. ICSI is a common technique utilized commercially to produce live foals, while the implementation of repeatable and successful IVF remains in the infancy stages.

He said researchers have been working on the elusive goal of making equine IVF possible for more than 35 years, so being part of the first rung in the latter of successful outcomes is meaningful. 

The research was supported in part by a National Needs Fellowship from the U.S. Department of Agriculture National Institute of Food and Agriculture (USDA-NIFA) and in part by the multi-state research project, the Germ Cell and Embryo Development and Manipulation for the Improvement of Livestock.