Weaning and Beyond: Impact of Embryo Transfer on Foals

Removing an embryo from a pony and transferring it to a larger mare, or vice versa, results in altered fetal growth and glucose metabolism. More specifically, one study showed that pony foals from draft mares were larger at birth and at weaning, whereas American Saddlebred foals from pony mares were smaller at birth until weaning. In addition, both groups of foals had altered blood sugar values that were perceived as adaptive responses to their plane of nutrition.

In a subsequent study*, those same researchers assessed weight and glucose metabolism on “enhanced” pregnancy (i.e., pony and Saddlebred foals transferred to draft mares) and “restricted” pregnancies (i.e., Saddlebred foals transferred to pony mares) after weaning. Key findings included:

• Pony-in-draft foals remained heavier than the pony-in-pony controls at 180 (time of weaning), 360, and 540 days after gestation;
• Saddlebred-in-pony foals were lighter than Saddlebred-in-draft foals on day 180 but caught up by day 540; and
• Insulin sensitivity was similar among the different pony groups, whereas insulin sensitivity was higher in the Saddlebred-in-pony group than Saddlebred-in-draft group on day 200.

“This study is important because changes in glucose metabolism and insulin sensitivity are associated with laminitis, obesity, metabolic syndrome, and osteochondrosis,” explained Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research. “Thus, understanding factors that contribute to glucose dysregulation will improve the lives and health of horses.”

These results confirm that environment, as well as glucose and insulin dynamics, affects fetal growth even after weaning and that specific selection of recipient mares in embryo-transfer programs is important. The researchers concluded that “the choice of broodmares is an essential component of a foal’s future health.”

*Peugnet, P., L. Wimel, G. Duchamp, et al. Enhanced or reduced fetal growth induced by embryo transfer into smaller or larger breeds alters postnatal growth and metabolism in weaned horses. Journal of Equine Veterinary Science. In press.