Q. What recommendations do you have for feeding a horse with equine metabolic syndrome (EMS) a low-carb diet, and is low-carb and sugar-free the same thing?

A. This is a great question and gets at one of my biggest concerns as a nutritionist, which is the belief that all horses with EMS need “low-carb” or even “no-carb” diets.

“What?!” I hear you say, “But I thought EMS horses couldn’t have starch and sugar.” That is a truer statement, although not completely accurate either. Now, I know you are probably completely confused! Let me explain.

Understanding Different Carbohydrates

The horse’s body uses types of carbohydrate, and the key is to understand the difference. There’s starch, or sugars such as glucose, and other sugars that break down into glucose in the small intestine; but there are also complex carbohydrates such as hemicellulose, cellulose, pectins, and lignin. These complex carbohydrates are digested in the hindgut by bacteria and don’t result in elevated insulin levels. For horses relying mainly on forage as a large proportion of their diet, these complex carbohydrates provide the majority of their daily calorie intake.

So to say that a horse needs a “low-carb” or “no-carb” diet is false: All horses need carbs, but EMS horses require a diet lower in starch and simple sugars, often referred to as non-structural carbohydrates (NSC).

You might be asking, “Is this sugar-free then?” and the answer is probably not. Most hays, even with low NSC, still contain a small percentage of simple sugars, and many have some level of more complex sugars, called fructans, as well. The goal is to reduce the total intake of starch and simple sugars to below about 10-12%. Research shows keeping NSC at or below these low levels helps maintain more stable insulin levels, which is a key component of managing insulin-resistant EMS horses.

How much each horse can handle is an individual thing. Horses with EMS that are in good weight, currently sound, and able to work might better handle slightly more NSC in their diet than laminitic and/or obese horses.

Finding the Right Forage

Because the foundation of any horse’s diet should consist of forage (i.e., hay, legumes, beet pulp, etc.), it’s important for the EMS horse to consume forage that has a low NSC level. The only way to know for sure is to test the hay at a lab, which is a relatively inexpensive (about $30 depending on the lab). Tests performed need to at least determine the forage’s carbohydrate profile; but it’s also worth having the forage’s mineral and protein levels checked as well. Testing requires taking a proper sample ideally using a hay corer to sample at least 15 bales. If hay changes frequently then testing might not be worthwhile as each batch will be different.

If feeding untested hay to a horse requiring a low-carb diet, you should soak the hay to wash out some of its water-soluble sugars (soak they for 30-60 minutes if using cold water—any longer than that and other nutrients might be lost). Note, however, that while soaking hay will lower its sugar content, it might not lower it to the ideal NSC range of 10-12% NSCs.

Typically, nutritionists and veterinarians recommend grass hays for horses with EMS, even though alfalfa (a legume) has a low glycemic index, which means it doesn’t tend to cause blood-glucose and insulin spikes. Alfalfa is, however, higher in calories than grass hay, meaning easy-keeping EMS horses would require less alfalfa than other forages. Less daily forage intake can have a negative effect on gastrointestinal health and cause well as boredom, so I typically do not recommend alfalfa to horses with EMS.

Instead, mature grass hay is a good option. As grasses mature they develop a greater proportion of complex structural carbohydrates relative to NSC. They’re also lower calorie than less mature grass hays, which means you can feed more before you reach the horse’s maximum calorie intake. For easy keepers who are often having their intakes whittled down to the bare minimum this can be a very good thing.

Make Sure EMS Horses Get the Nutrients They Need

Often, my clients with EMS horses reduce the amount of forage they provide to avoid obesity in their animals. Unfortunately, this can result in diets deficient in trace mineral and vitamins. It’s important, therefore, to supplement for these missing pieces. For horses that can tolerate extra calories, a high-protein ration balancer is a nice addition. These feeds have a small 1- to 2-pound serving per day and insure good quality protein in the diet and provide necessary trace minerals and vitamins. For horses that shouldn’t consume extra calories, equine nutrition companies have formulated heavily fortified supplements fed in 3- to 4-ounce servings. These supplements don’t offer much protein but typically have added essential amino acids.

Omega-3, Magnesium, and Psyllium Supplementation

Horses with EMS might also benefit from omega-3 fatty acids and magnesium supplementation. Some research suggesting that, at least in the short term, omega-3 fatty acids could help improve insulin sensitivity. Similarly, daily psyllium supplementation might also help; however if you feed psyllium daily, it might lose its sand-clearing effectiveness.

Whether magnesium will EMS horses depends on whether the diet you’re feeding is already providing enough magnesium or not. If it is, then supplementing more will probably have little effect. Some magnesium supplements have added chromium, which might or might not be beneficial but is unlikely to be detrimental. However, too much magnesium can result in loose manure, so don’t get carried away.

Take-Home Message

Feeding EMS horses a balanced, low-NSC diet is key to their successful management. Insuring that all nutrient needs are met and means all the horse’s metabolic pathways have what they need to efficiently and optimally function. This will give your horse the best chance of staying healthy, in good weight, and will hopefully help avoid laminitic episodes.