The demands of pregnancy bring about physiological changes in animals and humans alike. One of those adaptations involves the metabolic process, and a team of researchers recently set out to determine how insulin sensitivity and glucose levels differ in pregnant mares from nonpregnant mares.

A team of researchers at the Virginia-Maryland Regional College of Veterinary Medicine examined 32 healthy pasture-fed Thoroughbred mares, 22 of which were in foal and 10 of which were not.

The researchers performed an intravenous glucose tolerance test to measure insulin sensitivity, acute insulin response to glucose, and glucose effectiveness when the pregnant mares were between 25 and 31 weeks of gestation (Period 1).

The mares were then divided into two groups–both of which included pregnant and nonpregnant mares. One group was fed a high-starch supplement (39% starch; starches are known to induce a high glycemic response) and the other a high-fat/fiber supplement (14% fat/70% fiber, which elicits a lower glycemic response). Further, the researchers collected hourly blood samples from a subset of 12 mares over a 24-hour period to measure insulin and glucose levels in response to ingesting the feed supplements. Insulin sensitivity and other measures of glucose and insulin dynamics were again assessed at 47 weeks of gestation (Period 2)