A low-nonstructural-carbohydrate (NSC, which includes starch and water-soluble carbohydrates like simple sugars and fructans) diet is only one part of the menu when you’re planning how to feed a horse with insulin dysregulation (ID). What you must remember is animals are all individuals.

“Probably my biggest take-home message is horses and ponies are very individual in their insulin response to any particular diet. And if you are really concerned, you need to check the response of that individual horse on their diet,” said P.A. Harris MA, VetMB, PhD, Dipl. ECVCN, MRCVS, RCVS Specialist Clinical Nutrition (equine), Head of WALTHAM Equine Studies Group at the Waltham Petcare Science Institute, and Director of Science for Mars Horsecare. She reviewed considerations when feeding ID horses at the 2022 American Association of Equine Practitioners Convention held Nov. 18-22 in San Antonio, Texas.

As for the actual diet, “the first thing to do is fairly obvious: We need to remove all cereal and cereal-based feeds,” Harris said.

The goal is to produce a low insulin response to any feed or forage being eaten, Harris said. And yes, that means feeding low-NSC feeds and forages (be that fresh grass or hay/haylage). “The key question we are now asking is how low should the NSC be?” she said.

In a 2022 study, Harris and researchers from the University of Kentucky found horses with more severe ID had “very exaggerated insulin responses, even when they were being fed only around 500 grams to a 500-kilogram animal of feeds ranging from as low as 15% NSC on a dry matter basis,” Harris said. “However, they did not respond when we fed a very low NSC diet, which suggests it wasn’t eating itself that caused the response.”

Harris said in the more severe ID animals, therefore, feeding only extremely low amounts (down to less than 0.1g/kg body weight/meal) of NSC might be required, and small, frequent meals might be an important key. This is still being studied, she added, and not all animals will need to be fed such low levels.

What Are Your Goals?

When putting your low NSC ration together, said Harris, consider your weight goals for the animal. Are you trying to maintain weight, or do they need to gain or lose weight/condition? If you’re trying to help the horse gain weight, “we need to consider supplementing with feedstuffs that are very low in NSC but include ingredients such as vegetable oil (nonrancid, suitable for feeding horses, and don’t forget to think about vitamin E intake),” Harris said. “Or various highly digestible fiber feedstuffs that are also very low in NSC, such as soya hulls and un-molassed sugar beet pulp. Remember to continue to provide plenty of low-NSC forage.”

Often, however, with the ID horse your goal will be weight loss. In that case, “we need to feed restricted amounts of energy,” Harris said. “But when we’re doing that, we still must provide a balanced diet with sufficient low-NSC forage. Exactly what diet needs to be fed will depend on the individual animal, but if basing the diet on restricted amounts of forage, this often means using some way of increasing the time spent chewing, and you must think about adding a balancer.”

Consider, for example, feeding small amounts of low-NSC, low-energy chaff to extend feeding times when dealing with a weight management or weight loss case, she said.

Forage Types

Pasture, during certain times of the year, can have the same impact on blood insulin levels as grain. Remember that grass types differ. Harris explained that cool-season grasses tend to have higher levels of water-soluble carbohydrates (WSC), and warm-season grasses tend to have lower levels. However, wide variations can occur. Some warm-season grasses will have more WSC than some cool-season grasses, as can the hays made from them. You might need to test the WSCs in what you’re feeding, she said.

“Currently, we recommend that grass hay should be less than 12% NSC on a dry matter basis, and some animals might need less than 10%,” Harris said. “Again, if concerned, it is important to test your animal’s response to their own forage.”

It is often worth getting specialist advice on what forage is best for your horse, because there are other factors to consider with respect to pasture and hay. Certain teff hays, for example, might make your horse flunk a dope test if competing at the FEI level, Harris noted.

While more mature grass hays tend to have lower energy and WSC content, they can increase certain horses’ colic risk, especially if not introduced gradually. Remember that maturity does not automatically mean the same thing as “cut,” said Harris. In the U.S., later cuts tend to be more immature, but in Europe it is often the other way around. Getting appropriate advice about your hay can be very helpful, she said.

While soaking hay can reduce its WSC content, the impact of soaking hay is hard to predict, Harris noted. Therefore, she recommends trying to start with as low a WSC hay as possible. If concerned, get the wet hay analyzed or test the horse’s insulin response to the soaked hay, she said.

If feeding soaked hay, “under most circumstances you must use a balancer, especially if the diet is forage-based,” Harris said. Soaking risks losing dry matter (which must be considered when putting together a weight loss diet), as well as protein and certain minerals and vitamins.

Turnout Considerations

When to turn your horses out on pasture varies regionally (consult with a local nutritionist), but the advice is generally to turn out early morning and remove from pasture by mid-morning, said Harris. However, at certain times of the year (such as in spring when pasture is green and growing rapidly), laminitis-prone animals should get no or very limited turnout.

Pasture management also matters, as stressed pastures can have more WSCs. It might be worth talking to an appropriate specialist to learn about your grass type and how your management might be impacting the WSC concentrations, said Harris.

Grazing muzzles can be helpful as one part of a weight management program but must fit correctly, and the horse must be confident in using them. Additionally, if you take the muzzle off and leave the horse on grass, “this can result in compensatory intake and potentially an increased risk of weight gain and laminitis,” Harris warned.

Take-Home Message

Harris concluded by emphasizing the importance of seeking nutritional advice that is tailored to your individual animal, especially in complex cases, from a veterinarian and a nutritionist working together as a team. Monitoring these horses is essential, especially those at high risk of developing laminitis, and it is important to consider the insulin response to all aspects of the ration (e.g., all complementary feeds, any supplements as well as the preserved and fresh forage).