Mare to foal: Let's talk.

The struggle to discover reasons for early embryo loss continues.

An article by Clare Illingworth, SPARK writer, University of Guelph.


Early pregnancy loss in horses is all too common. It’s believed that more than 90 per cent of breeding attempts result in an initial pregnancy, but up to 30 per cent of these are lost in the first month. Besides the anguish, early pregnancy loss costs the industry millions each year in extra veterinary visits and multiple inseminations. In addition, the delayed pregnancy can push foaling outside of the desired season. University of Guelph researchers are taking another step towards finding out why this happens, by better understanding exactly how development occurs in early pregnancy, so they can predict which mares are likely to have problems.

By determining the factors leading to this pregnancy loss, Prof. Keith Bet-teridge, Department of Biomedical Sciences, hopes to eventually create a test for mare fertility that could weed out horses likely to be poor candidates for full-term pregnancy.

“Successful reproduction is imperative to the survival of many sectors in the equine industry,” says Betteridge, a pioneer in inves-tigating how the conceptus (the embryo and its surrounding membranes) attaches to the uterus lining. “By identifying the molecular background to embryo loss, we could test potential broodmares, recognizing early the less fertile mares.”

The equine conceptus reaches the uterus five to six days after fertilization as a compact ball of cells inside a soft “shell” that, at first, moves around in the uterus. Soon, its interior hollows out and fills with fluid as it expands. At 16 to 17 days after fertilization, the conceptus comes to rest at the site of its future attachment to the uterine wall, where it can exchange nutrients and waste products with the mother, as well as grow.

Researchers don’t know how the attachment site is chosen in nature, but Betteridge believes the conceptus and the mare give chemical signals to each other. If they’re not in unison, the pregnancy can be lost. “We’ll be trying to iden-tify those signals,” he says. His research team is conducting biochem-ical and molecular studies of horse embryos to identify an array of hormones and other molecules involved in the attachment pro-cess. By continuing research into the conceptus, Betteridge hopes to improve equine pregnancy statistics. But he knows there’s still much work to be done.

“Research into something like embryo development is like a giant puzzle. I’ve been putting small pieces into this puzzle for 30 years.”

Also involved in this study are Prof. Tony Hayes, Department of Patho-biology; Prof. Rudolf Waelchli, Department of Biomedical Sciences; and student Laura Crews. This research is sponsored by the E.P. Taylor Research Trust and the Ontario Ministry of Agriculture and Food.