Molly mules can’t reproduce naturally. But researchers found they can make excellent surrogate dams for embryo transfer. | Photo: Courtesy Dr. Eduardo L. Gastal, Southern Illinois University

“Mules can host the embryo of a mare, gestate normally, produce a good amount of milk, and have an incredible maternal instinct and ability,” said Eduardo L. Gastal, DVM, MS, PhD, Professor in the Department of Animal Science, Food and Nutrition at Southern Illinois University, in Carbondale.

“It’s curious for a hybrid that doesn’t usually have offspring to be such a good mother like this,” Gastal said. “It’s an amazing thing to see.”

In their study, Gastal and his fellow researchers transferred 8-day-old horse embryos into two groups of recipients: seven cyclic horse mares and seven acyclic mules. For the horse recipients, the scientists synthetically synchronized the reproductive cycle of the recipient with the donor mare. For mules, however, the research team prepared them with hormonal treatments (estrogen and progestogen). They then followed the pregnancies with ultrasound and blood sampling