Surrogate Mares' Impact on Embryo Transfer Foals Evaluated

Surrogate Mares' Impact on Embryo Transfer Foals Evaluated

At birth, pony foals from draft mare surrogates were 57% heavier than pony foals from pony mare surrogates.

Photo: Courtesy Pauline Peugnet, PhD

As embryo transfer becomes more common in equine reproduction, researchers are discovering the importance of surrogate mare selection for optimum foal growth and metabolic health.

Recently, French scientists implanted embryos from ponies, light saddle horses, and draft horses into surrogate mares of different sizes and observed significant differences in weight, height, barrel circumference, and metabolic markers among the resulting genetic half-siblings, said Pauline Peugnet, PhD, of the French Agricultural Research Institute in Jouy-en-Josas. Peugnet presented her study at the 2014 French Equine Research Day, held March 18 in Paris.

These effects not only influence the animal’s growth potential, but also its metabolism, which can play a role in insulin resistance and perhaps even osteochondrosis (a developmental orthopedic disorder) development, she said.

In the study conducted over two breeding seasons, Peugnet and her colleagues worked with 22 Welsh pony mares, 28 light saddle horse (mostly Selle Français and Anglo-Arab) mares, and 22 draft horse (Comtois and Breton) mares as surrogate embryo-recipient mares. To keep data as comparable as possible, they employed the same pony stallion for all pony foals and two saddle horse stallions for all saddle horse foals. The researchers did not use a draft stallion, as they only produced pony and saddle horse foals.

At the end of the study, the researchers had observed:

  • Six pony foals gestated in draft mares;
  • Eight saddle horse foals gestated in draft mares; 
  • Six saddle horse foals gestated in pony mares;
  • 21 pony foals gestated in pony mares (a control group, used for comparing to the test foals); and
  • 28 saddle horse foals in saddle horse mares (another control group).

At birth, pony foals from draft mare surrogates were 57% heavier than pony foals from pony mare surrogates, Peugnet said. But despite the former foals being so much bigger, they were actually born about a week earlier than the latter foals.

Saddle horse foals from pony surrogates stayed in utero about two weeks longer than those from the larger mares, but were about 37% lighter than the saddle foals born to draft and saddle mares.

Photo: Courtesy Pauline Peugnet, PhD

Saddle horse foals from draft horse surrogates were no heavier at birth than those born to saddle horse mares, Peugnet said, and gestation time was about the same for both groups.

Saddle horse foals from pony surrogates, on the other hand, stayed in utero about two weeks longer than those from the larger mares, she said. That extra time didn’t make them any bigger than their half-siblings, though. At birth, they were about 37% lighter than the saddle foals born to draft and saddle mares.

At 1 year old, ponies from draft mares were still 37% heavier—and significantly taller and more broad-chested—than ponies from pony mares, Peugnet said.

Saddle foals born to pony surrogates caught up in weight with the other groups temporarily, but by a year of age, they were nearly 30% behind the other groups. They were almost as tall; however, the pony-born saddle horses had shorter front legs than those born to draft and saddle mares and were significantly thinner around the barrel.

Metabolic rates varied significantly from one group to the other as well, Peugnet said. Although the data is still being analyzed, faster fetal growth appeared to have an unfavorable effect on insulin sensitivity. For example, pony foals in draft mares showed signs of increased insulin resistance (IR) from birth, whereas the pony-in-pony foals did not show signs of IR until weaning. The researchers have not yet confirmed a relationship between osteochondrosis risks and surrogate mare choice, but further analyses are still in progress.

“The concept of long-term fetal programming of a horse’s health has now been verified,” Peugnet said. “All environmental factors susceptible of interacting with the intra-uterine environment should therefore be considered in the management of the gestating mare.

“In breeding practices involving embryo transfer, particular care must be taken when selecting the surrogate mare,” she said. “This is especially true for conformation, but also with regard metabolism, as each breed has its own morphological and physiological characteristics.”

Peugnet’s research is ongoing.

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More

Free Newsletters

Sign up for the latest in:

From our partners