Do Recipient Mares Pass Traits to Foals?

One researcher describes what we know about the receiving mare’s effect on the foal in embryo transfer scenarios.
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Do Recipient Mares Pass Traits on to Foals
Much of the available data describes the effect of recipient mare vs. donor mare size, and how it affects foal growth. | Photo: iStock
Q.I have two registered Warmblood mares. I plan to ride both in competition but I also would like to get offspring from them. On the other hand, I have two unregistered mares big enough for receiving the embryos, but they aren’t Warmbloods. One is a ­Haflinger-Schwarzwälder cross, and the other a Standardbred cross. A friend of mine suggested that both receiving mares would influence the foals—especially regarding future performance ­records—in a negative way. Is there any proof or research available about the receiving mare’s effect on the foal?

Jessica Wieland, Germany

A. There is data available indicating that the recipient mare does influence a foal’s traits. Most of this describes the effect of recipient mare size in comparison to that of the donor mare. In a study on transfer of pony embryos to either pony or draft mares, a ­research group in Poland found that at maturity (4 ½ years) the pony-in-draft foals were 1.5 to 2.5 inches higher at the withers than those in pony mares, and they also had proportionately longer front legs, especially the cannons, which were almost 10% longer in proportion to body size.

These findings were supported by a study in England in which foals resulting from pony embryos transferred to Thoroughbreds were compared to foals ­resulting from Thoroughbred embryos transferred to ponies, and both were compared to their same-size recipient controls. The foals from embryos transferred to the “wrong” size mares were different from their control siblings not only in weight and height at birth but also in their growth patterns. At 3 years, the foals’ body weight, length from head to tail, girth, cannon bone circumference, and forearm and cannon bone lengths differed from those of the control foals. In another study by the same group, foals from identical twin embryos that had been transferred to different-size recipient mares differed three inches in height at the withers at ­adulthood

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Written by:

Katrin Hinrichs, DVM, PhD, Dipl. ACT, is a professor and the Patsy Link Chair in Mare Reproductive Studies in the Department of Physiology and Pharmacology at Texas A&M’s College of Veterinary Medicine and Biomedical Sciences.

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