More than a decade after they were collected, samples of equine embryonic losses from early studies are proving useful to researchers today. The value of long-term studies is well understood by researcher Dr. Keith Betteridge, who has been involved with Ontario Veterinary College equine reproduction studies since 1986. Betteridge has seen reproduction technology evolve. “Pregnancy was always looked at as though the embryo was just a passenger in the uterus,” he said. “In 1960s emerged that the embryo is a very active participant in pregnancy. If the embryo is not communicating with the mare, the pregnancy won’t develop. “Understanding the two sides of the conversation (embryo-mare) is absolutely vital to understanding how pregnancy will develop normally and how, when an embryo is lost, the pregnancy will fail.” He described how the equine embryo is truly unique with its unusual coating (called a capsule). With ultrasound, an embryo can be detected as early as nine days in. Betteridge said about 17% of equine pregnancies fail and 70% of those losses will occur in the first six weeks of pregnancy. RNA sequencing has provided new methods of finding out which genes are active in the lining of the uterus at a particular time. The ‘dialogue’ from the mare’s side has been examined and future studies will hopefully reveal the ‘conversation’ from the embryonic side. With continued research, information is gradually building up that will help the horse breeder reduce the number of pregnancies that are lost.