Feeding Straw to the Insulin Resistant Horse May Be a Mistake

By Juliet M. Getty, Ph.D.

Your horse is a grazing animal; he needs access to grass or hay all the time, all day and all night. Left with an empty stomach, the horse may develop ulcers, be prone to colic, experience laminitis or its relapse, and exhibit sensitive, irritable behavior. If you have an overweight horse, the hormonal stress response to forage restriction will actually keep him from losing weight. The solution? In short, provide low starch/low sugar forage and get your horse moving.

Straw is often touted as a low NSC (non-structural carbohydrates) feed source for insulin resistant horses because, while not terribly nutritious, it can “keep them busy” in between hay feedings. After all, straw is just empty calories, right?  The answer may surprise you.

What is straw?

Straw is the dried stalks of cereal plants such as wheat or oats, but it generally contains no grain kernels (as we often see with oat hay, for example). After the grain is harvested, the stalks are left standing to dry. They are then cut and baled. Typically, straw is used for animal bedding or industrial usages. It is not a worthwhile food source mainly because it is very high in lignin, a fibrous substance that binds nutrients and cannot be digested by the microbial population in the horse’s hindgut. The NDF (neutral detergent fiber) value of straw tends to be high, meaning it is not digestible, and hence, provides few calories. But, before it reaches the horse’s hindgut, the carbohydrates, fats, and protein are extracted and digested inside the small intestine. Non-structural carbohydrates (NSC), which include sugars, fructans, and starch, are a concern when feeding the insulin resistant horse. So the questions become: “Is straw low enough in NSC?” and “How does it compare to other commonly fed forages?”

Every forage is unique; its nutritional content will vary depending on the soil, amount of rainfall, exposure to sunlight, and degree of stress. Consequently, testing is the only true way to know what is in your hay, or what is in straw. Some straw will test low enough in sugar and starch to best safe to feed to an insulin resistant horse, but oftentimes this is not the case. Most farms (unless they use it as bedding) do not have enough straw on hand to warrant testing it, so feeding it may not be worth the risk.

Ideal values for the insulin resistant horse

To determine whether a forage is safe to feed free-choice to an insulin resistant horse, pay attention to three key indicators:

  1. NSC: Ideally, the NSC value of your forage should be less than 13% on an dry matter basis (approximately 12% on a as-sampled basis).
  2. ESC + Starch: This represents the simple sugars plus starch. It should be less than 11% on a dry matter basis (approximately 10% on a as-sampled basis). Since NSC includes fructans (which do not significantly contribute to blood insulin levels), this second indicator is worth evaluating, especially if the NSC value of your forage is slightly above 13%.
  3. DE: For the overweight horse, it is important to reduce calories. Ideally, the DE (caloric) content should not exceed 0.94 Mcals/lb (2.06 Mcals/kg) on a dry matter basis (approximately .88 Mcals/lb or .94 Mcals/kg on an as-sampled basis).

Over the past 12 years, Equi-Analytical Labs has compiled normal ranges of key nutrients in forages. The chart below compares straw to various types of hay.


Normal Ranges of Key Nutritional Indicators of Straw Compared to Other Forages1
(on an as-sampled basis)


Alfalfa hay

Grass hay
(cool season)

Bermuda grass hay
(warm season)

Oat hay

DE Mcals/lb
(Digestible Energy)






(Neutral Detergent Fiber)






(Water Soluble Carbohydrates)






(Ethanol Soluble Carbohydrates)












(WSC + Starch)






ESC + Starch







The table above offers several significant points

 Evaluating NSC levels:

  • The NSC range of straw may be generally low, but it can be as high as 17.1%, which is unacceptable for the insulin resistant horse. 
  • Alfalfa, often touted as high in sugar, has an NSC range that is reasonable and predictable.
  • The NSC range of grass hays (both cool and warm season) is broad, highlighting the need for testing. 
  • Grain hays (from oats, as shown above, but which can also include barley, wheat, rye and millet) tend to be quite high in NSC.

ESC + Starch values parallel the NSC levels of each forage type. Forage safety cannot be assumed; testing is the only way to take the guesswork out of feeding.

DE variations exist. The DE of straw tends to be low. Alfalfa’s caloric content is higher due to its protein content. Many grass hays have a low enough DE to be suitable for the overweight horse, but this is not always the case.

The NDF percentage in straw is high, even at its lowest range level. If the NDF value is greater than 60%, the forage contains a large amount of indigestible fiber, making it lower in feed value for your horse. With straw, the concern is not feed value; the high NDF appears to be a good thing. But its coarseness makes it difficult to chew and swallow, and more significantly, can lead to impaction colic. 


Straw may seem like the ideal way to fill in the time between hay feedings for the insulin resistant horse, but it is not likely worth the risk. It can be as high or even higher in sugar/starch as grass hay. And because it is extremely dry and coarse, feeding it increases the risk of the horse developing colic. A better way is to test your grass hay to confirm that it is suitable to feed free-choice, thereby feeding your horse the way his predecessors remained healthy for millions of years. Respect his need to be what he is – a horse.

1Source: www.Equi-Analytical.com forage analyses ranges over last 12 years.

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For permission to reprint this article, in part or in its entirety, please contact Dr. Juliet Getty directly at Gettyequinenutrition@gmail.com.