Your horse has been diagnosed as insulin resistant. Your vet advises you to
➡ feed low sugar/starch hay,
➡ restrict turnout to a dry lot, withhold grazing,
➡ eliminate all buckets and treats, except for soaked
beet pulp.
If the insulin numbers don’t come down, the next step will be to soak the hay to leach out some of the sugars.
If that doesn’t work, then try metformin or SGLT2 inhibitors.
You enter panic mode. You read up on the internet. Sure enough, those are common recommendations. You take a deep breath.
Background
Insulin rises after a meal
It’s been shown that insulin rises after eating a meal, with the highest insulin numbers occurring between 60 and 90 minutes.
Horses that do not have insulin resistance. Normal insulin values are roughly under 10 uUI/mL. In horses that are NOT insulin resistant, their insulin numbers may rise to about 20 or even 30 uUI/mL after a carbohydrate meal.
Horses with insulin resistance. Although normal baseline insulin values are under 10 uUI/mL, horses with insulin resistance may have their baseline numbers elevated to 30-40 uUI/mL, or even higher. We know that horses may experience foot soreness if the insulin numbers reach about 60 at baseline.
What’s also different with insulin resistant horses is that they have a larger insulin response to the foods they eat. It’s not unusual for an insulin resistant horse to have a baseline of 30 and rise to about 60 after a meal. To get the most accurate blood results, it’s important to draw blood on a horse that has had hay, but not a grain meal.
The goal with insulin resistant horses is to keep the insulin numbers down.
Supplements
In a previous newsletter, we discussed the use of resveratrol to potentially reduce the size of the insulin rise after a meal. Available here. In that article, we talked about the insulin curve in the horses that were responders to resveratrol supplementation, compared to the horses that were not responders.
The big question
Is the insulin curve related to the % of sugar and starch in the feed?
Or, is it related to the amount of sugar and starch (by weight) of the total meal?
New research shows that it’s related to the total amount of sugar and starch in that meal in grams, not by percentage.
What does this potentially mean in the real world?
If this new research is valid, to lower the insulin levels after a meal, you could:
» Feed a low sugar/starch meal. An example of this would be. Feed 3 kg (6.6 lbs) of 10% hay = 300 grams of sugar/starch.
» Feed a moderate sugar/starch meal, but make the meal size
smaller. Feed 2 kg (4.4 lbs) of 14% hay = 280 grams of sugar/starch.
Additional research is needed to verify that this would hold true.
◆︎ What we don’t know:
From this new research, there are many unanswered questions.
☛ Can you reduce the insulin increases by feeding multiple small meals per day?
☛ How does a small holed hay net affect the insulin peak?
☛ Can you add a small amount of wheat bran, carrot pieces, or berries to a horse’s bucket to make it tastier – as long as the total grams of sugar and starch are low?
☛ The research was completed utilizing a pelleted feed. Is the insulin response the same if the feed was straight hay?
This also causes one to question the methodology of other research that has been done. For instance, an article published in a peer reviewed journal, reported that high protein levels caused an exaggerated insulin response in insulin resistant horses. Was it the high protein by percentage?
Or was this a similar case in which the insulin response was based on the total amount in grams of sugar/starch, or even protein, instead of the percentage?
The current research sheds new light on post-meal insulin rises. But it leaves as many questions as it answers. It will be fascinating to see the developments based on future research.
We do the best that we can do for our horses. Understanding how meal feeding affects our horses is a part of that.
Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay 2025