Science Friday with Dr .Gustafson -- Choosing hay safe for metabolic equines.
10/02/2026
I love science and understanding how things work. I love knowing stuff but love not knowing stuff even more because it provides an opportunity to learn, maybe dig a little deeper and find out what else you don’t know.
As President and Research Advisor, I often write posts for the ECIR Group social media pages in the hopes that people may learn something useful. Sometimes I get comments that it’s too technical or too detailed. Sometimes people express gratitude for understanding something that they were struggling with.
My role here is not to make things more complicated and unwieldy. Therefore, I plan to confine my musings to Fridays, so that we may have a “Science Friday” (sometimes) when I have the time. Don’t hesitate to ask about topics you are interested in. Maybe there is a published paper or some controversy (What?! In the equine world?) for which you would like a better understanding.
For today’s topic I want to discuss something I heard on a recent podcast between two experts discussing what index to use as a threshold for dietary carbohydrate safety in horses with high insulin. The question was whether to use NSC or ESC. I had to rewind it several times to be sure I was hearing the question correctly. Remember, NSC = WSC + starch; i.e., fructans, simple sugars, and starch. ESC is primarily a measure of simple sugars (glucose, fructose, sucrose). The answer came back as, “Use NSC because it includes starch.” I was surprised by this response, because I cannot imagine that any nutritionist or expert in EMS would only use ESC and exclude starch. Starch is a string of glucose molecules and when broken down (hydrolyzed) is absorbed as glucose. If you follow the ECIR Group, you know that we’ve been promoting the use of hydrolyzable carbohydrates (HC) as the index for safety. HC = sum of ESC + starch.
As we’ve said so many times, fructans found in cool-season grasses do not influence glucose and insulin and there was some dodgy agreement from the experts on that topic. However, the recommendation of the Equine Endocrinology Group is still less than 10% NSC. Results will vary by region, but using the data in my forage database, that would rule out all but 13% of the samples, or put another way, you would need to soak 87% of the sampled hays to reduce the NSC. Of these same hays, only 3% have HC >10%. As if managing horses with metabolic disorders isn’t challenging enough, this unnecessary threshold of less than 10% NSC increases the difficulty of finding safe forage. Furthermore, soaking is a waste of water resources, increases the overall burden, and can be challenging in the winter.
Kathleen Gustafson, PhD
President and Research Advisor, ECIR Group Inc.
