Fetal Growth and Nutrition in Embryo Transfer Programs

Embryo transfer (ET) is an important part of  many breeding programs, especially if mares are actively competing or have difficulty staying in foal after breeding. But recipient mares add a layer of complexity in their effect on the resulting foal.  

Breeding managers consider the genetics of the donor mare and the stallion, but both nutrition and a “newer” field of genetics—called epigenetics—also greatly influence the growth and development of the foal.

The nutrients delivered to the foal depend somewhat on the size of the recipient mare’s uterus. In many species, it is already known that any reduction in growth rate in utero has long-term repercussions. For example, people who were in utero during the Dutch Famine of World War II were later prone to developing obesity, glucose intolerance, high blood pressure, or cardiovascular diseases later in life.

The long-term impact of a poor state of nutrition in utero has not been previously demonstrated in horses. Researchers* enhanced or restricted fetal growth by transferring pony or Saddlebred fetuses into draft mares (i.e., enhanced growth) or Saddlebred fetuses into pony mares (i.e., restricted growth). The foals were followed from birth until weaning.

Key findings of the study included:

• Pony foals from draft mares were larger at birth and remained larger until the end of the study at weaning;
• Saddlebred foals from pony mares were smaller at birth and remained smaller until the end of the study at weaning, and;
• Both groups of foals had altered glucose (blood sugar) values that were perceived as adaptive responses to their plane of nutrition. Specifically, insulin resistance occurred in “pony-in-draft” foals but insulin sensitivity occurred in “saddlebred-in-pony” foals.

The researchers concluded that altered fetal growth affected glucose metabolism, which may affect future capacity to perform in equestrian sports. In addition, altered fetal growth induces an increased susceptibility to metabolic diseases later in life, which may be of importance in the presence of an increasing prevalence of equine metabolic syndrome.

*Peugnet, P., L. Wimel, G. Duchamp, et al. 2014. Enhanced or reduced fetal growth induced by embryo transfer into smaller or larger breeds alters post-natal growth and metabolism in pre-weaning horses. PLoS ONE 9(7):e102044.