The maternal recognition of pregnancy (MRP), one of the earliest communications that occurs during pregnancy between the embryo and the mother, is the signal produced by the embryo alerting the mother’s body of the pregnancy.
Although the MRP signal is clearly understood in other domestic species, it remains a mystery in horses—a mystery that veterinary researchers at the University of Saskatchewan (USask) are hoping to solve.
“As a clinical doctor, I encounter mares regularly who fail to recognize that the pregnancy is there and the embryo is lost,” said Dr. Claire Card (DVM, PhD), a professor of theriogenology (animal reproduction) at the Western College of Veterinary Medicine (WCVM).
These pregnancy failures cause the equine industry to lose money as well as valuable genetics “because we don’t have a lot of the answers to these questions,” said Card.
“We would like to solve that so we could figure out treatments or ways to prevent that from happening. It’s a big problem for us.”
Card is collaborating with WCVM graduate student Dr. Mariana Diel de Amorim (DVM) and resident Dr. Maria Lopez (DVM) to investigate the MRP process in mares—a communication that they both consider key to a successful pregnancy.
Early pregnancy in horses is unique from other domestic species in several ways. First, the embryo must be fertilized and needs to secrete a molecule called prostaglandin E to descend into the uterus from the uterine tubes. Once inside, the equine embryo migrates throughout the uterus. It’s during this migration that the MRP signal most likely takes place.
“I would describe it as the time interval in which the embryo secretes a communication to the endometrium (lining of the uterus) and from the endometrium to the ovary in which the embryo is telling the mare, ‘I’m here—I’m here and please don’t destroy me,’” said Lopez.
The researchers are investigating the role of these prostaglandins, a family of compounds that are involved in many of the body’s processes and likely play a role in the MRP signal. Considerations such as when these prostaglandins turn on and off, how much of them are secreted, how the secretion is directed—all of these factors play a role in regulating biological processes.
Other scientists suggest that small quantities of two compounds—prostaglandin E and prostaglandin F—are combining and causing the mobility of the embryo through the whole uterus. But so far, that theory hasn’t been proven.
Since Card and Lopez suspect that the MRP signal relies on a change in the balance between prostaglandin E and prostaglandin F2 alpha, they are administering prostglandin E into the uterus of research mares—a process that alters the balance between the two compounds.
By observing the impact of that change on the MRP signal, they hope to gain a greater insight into the MRP process.
“The horse is probably quite distinct in the way that they recognize pregnancy, and it’s probably got its own special things that it does,” said Card. “We have some insight into what those are, but … it takes a big team to do this kind of work and it’s expensive.”
Card and her team’s research work is supported by a five-year, $140,000 research grant from Natural Sciences and Engineering Research Council of Canada.
Ashlyn Ketterer is a WCVM veterinary student who was part of the college’s Interprovincial Undergraduate Student Summer Research Program in 2019.