Testing Ponies for Insulin Resistance: Fasted or Fed?

Because ponies tend to be easy keepers and overweight, they are usually among the most commonly affected by insulin resistance (IR). Experts recommend testing horses and ponies suspected of being resistant to the effects of insulin to avoid or minimize the occurrence of laminitis, a painful, life-threatening condition.

Several tests for IR exist, including the intravenous glucose tolerance test (IVGTT) and the oral sugar test. While the IVGTT is touted as being superior, the oral sugar test is more practical and economical. Briefly, the oral sugar test involves administering corn syrup orally and taking one or two blood samples within 90 minute of corn syrup consumption to measure insulin levels.

Unfortunately, the oral sugar test involves an overnight fast.

“In many areas of the world, ponies are maintained on pasture, which makes an overnight fast challenging,” explained Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research (KER). She added, “Approximately 35% of horses in the United Kingdom and a substantial number in Australia and the United States are maintained on pasture 24/7.”

Pulling a horse off pasture and away from herdmates to isolate it overnight for an oral sugar test can be both inconvenient for the owner and stressful to the horse. In turn, a high level of stress and release of stress-related hormones may impact the results of the oral sugar test, making them invalid.

To facilitate IR testing, one British research group* evaluated the oral sugar test to determine if an overnight fast was actually necessary. To do this, 10 adult native British ponies were subjected to the oral sugar test either after being fed (i.e., remained on their regular pasture) or after being fasted in a separate, bare paddock.

The key finding of the study was that significant differences in insulin levels were obtained depending on whether the ponies were fasted or fed; however, the test could still be performed and interpreted under both testing conditions. The study also revealed that repeatability of the oral sugar test is low.

“This means that using the oral sugar test to monitor a horse’s or pony’s level of insulin dysregulation is not particularly helpful,” explained Crandell.

Once diagnosed, institute appropriate management strategies such as weight loss and exercise. “Consider a product such as I.R. Pellet, a supplement that balances the micronutrients in the diet yet adds only a minimal amount of calories,” suggested Crandell.

Source:Equinews