Managing Metabolic Horses: Latest Research and Guidelines

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Updated:

October 10, 2025

Feed & Nutrition, Autumn, Winter, Diseases, Prevention

By Madeline Boast, MSc, PAS

Our knowledge of optimal equine management is continually expanding. The science relied upon to make informed management decisions for our horses is changing as more research becomes available. One of the primary nutrition concerns across North America is the management of horses with metabolic health issues. This article will discuss the goals of nutritional management for these horses, how science has evolved, and updated guidelines based on the newest science for horse owners to follow.

Insulin Dysregulation

Insulin dysregulation (ID) is a term that encompasses both tissue insulin resistance, and/or resting/postprandial hyperinsulinemia. Postprandial hyperinsulinemia refers to elevated blood insulin after a meal. Horses with elevated blood insulin are at a higher risk of developing endocrinopathic laminitis (EL). EL is the most common form of laminitis.

Within the hoof are tissues called laminae, which hold the coffin bone within the hoof capsule. Inflammation of these tissues is referred to as laminitis. Not only is this condition extremely painful for the horse, but in severe cases the laminae tissue will separate and the coffin bone will rotate and sink within the hoof capsule; this is referred to as founder.

Across the industry, the prevalence of ID is increasing. It is hypothesized that this could be related to the increase in equine obesity, as horses with ID are often overweight. However, it is important to note that not all obese horses have ID, and lean horses can be diagnosed too.

Horses may also have health issues that predispose them to the development of ID. Pituitary pars intermedia dysfunction (PPID), also referred to as Cushing’s disease, impacts the hormone production in the horse, and ID is a common symptom of PPID. In these horses, the insulin levels are elevated due to the tissues not responding adequately to insulin. If your horse is diagnosed with PPID, close medical and nutritional management is warranted.

Nutritional Management

The goal of nutritional management is to maintain a healthy body condition score while preventing elevated blood insulin.

For optimal nutritional management, it is critical to understand how the equine digestive tract works. There are two main sectors — the foregut, and the hindgut. The foregut (stomach and small intestine) is where concentrate feeds are primarily digested and absorbed, whereas forages are primarily digested in the hindgut (cecum and colon).

Most of the enzymatic digestion for the horse occurs in the small intestine. This is where non-structural carbohydrates (NSCs) will be broken down and absorbed along with other nutrients such as protein and fats.

The foregut of the horse is the only part of the gastrointestinal (GI) tract that elicits a postprandial insulinemic response.¹

When a healthy horse consumes a meal that contains NSCs, this results in enzymatic breakdown and glucose being absorbed into the bloodstream. When glucose enters the bloodstream, the pancreas will release insulin in response to the elevated blood glucose. Insulin is the hormone that stimulates the cells to uptake the glucose so the horse is able to use it for energy.

diagram of the equine digestive system

When the insulin facilitates the uptake of glucose by the cells, the glucose content in the blood stream will then decrease. As the level of glucose decreases, the pancreas will reduce insulin secretion and all levels return to baseline.

However, in metabolic horses, the cells do not react properly to insulin, which results in an inadequate uptake of glucose from the cells. This means the blood glucose content remains elevated, which triggers the pancreas to continue secreting insulin. As insulin continues to be secreted, the level in the blood rises, which is referred to as hyperinsulinemia. For the health of horses with ID, it is critical to avoid large insulin spikes to, in turn, prevent hyperinsulinemia.

The fibrous feedstuffs, rich in structural carbohydrates, will pass through the small intestine with minimal digestion as they require fermentation. The fermentation takes place in the hindgut and results in the production of volatile fatty acids (VFAs), which serve as a major source of energy for the horse. This process does not result in the same blood insulin spike that can occur with the digestion and absorption of NSCs.

As the horse’s GI tract is designed to process forages, it is recommended to focus on that being the base of the program when formulating an equine diet.

Guidelines Previously Relied Upon

When searching the internet for guidelines to optimally support a horse with ID, the recommendations vary widely. Most commonly, the guideline of providing feed and forage with less than 12 percent NSC is recommended.

This guideline is based on a study that evaluated insulin responses to forages with varying NSC concentrations in horses with polysaccharide storage myopathy (PSSM).²The authors illustrated that forage with high NSC content produced higher insulin responses, which could in turn exacerbate PSSM symptoms.

The 12 percent NSC guideline is now widely used across the industry; however, the research was not completed on horses with metabolic disorders. When there is a lack of research, sometimes extrapolating data, such as in this case, can be helpful. But as more research is completed, it is critical that the industry follow those scientific advancements as we learn more about optimal management.

Commercial Concentrates

As previously noted, our understanding of optimal management for metabolic horses is expanding, supported by recent scientific publications.

Dr. Erica Macon, Assistant Professor of Equine Science at Texas A&M University, and her research team have proposed new feeding guidelines based on recent publications.

In aiming to identify the threshold of NSC components, eight different feeds were fed with an increasing amount of pure sugar and starch.³The NSC content ranged from 5.1 percent to 17.1 percent. With the feeds being fed at a rate of 1 g per kg body weight (BW), the NSC concentration ranged from 0.05 g NSC/kg BW to 0.19 g NSC/kg BW.

Both healthy horses and horses with ID were used in the study. As expected, horses with ID had higher insulin responses to all feeds compared with the healthy horses. However, the study found that when NSC content was below 0.1 g/kg BW, there was no exacerbated insulin response in the metabolic horses. Based on this research, the authors suggested that ID horses appear to have a threshold of 0.1 g NSC/kg BW per meal — beyond this level, they will have an exacerbated insulin response. This threshold is 17 times lower than the threshold of healthy horses.⁴

This is an important scientific advancement, as relying on the blanket statement that “less than 12 percent NSC is safe for a feed” is now outdated. If you manage or own a horse with metabolic health issues, it is recommended to complete the following calculation on their feed to ensure it is in line with the most up-to-date scientific guidelines.

Related: Caring for the Senior Horse

Prior to getting started, you will need an estimate of your horse’s weight, the weight of the feed, and the NSC content of the product. Keep a simple kitchen scale in the barn to be able to easily quantify the amount of product being fed to your horse.

Example Calculation

Information Required:

1) Horse’s ideal BW: 500 kg

2) NSC percent of commercial concentrate: 13 percent NSC (as fed basis)

3) Feeding rate for horse’s ideal BW based on manufacturer’s instructions or equine nutritionist’s recommendation: 570 g

Calculation Steps:

1) Convert the NSC percentage from an as-fed basis to a dry matter basis (DMB). Note that pelleted concentrates are 95 percent dry matter (DM). Textured concentrates are 90 percent DM.

(13% NSC as fed)/(95% DM) = NSC on DMB/100% DM = 13.7% NSC on a DM basis

2) Multiply the NSC on a DMB and the feeding rate.

(0.137 NSC DMB) x (570 g) = 78.09 g NSC in concentrate meal

3) Divide the grams of NSC in the concentrate by the horse’s BW in kilograms.

78.09 g NSC/500 kg BW = 0.157 or 0.16 g NSC/kg BW

4) This amount can then be compared to the research.

The 0.16 g NSC/kg BW is too high based on the most up-to-date research. Therefore, the amount should be divided into two meals daily to meet the recommended guidelines of below 0.1 g NSC/kg BW per meal.

5) When split into two meals, it is 39.04 g NSC/meal.

39.04 g NSC/500 kg BW = 0.07 g NSC/kg BW /meal
This brings the level into the recommended safe range.

Working with a qualified equine nutritionist to build a program that follows the most up-to-date scientific guidelines for the nutritional management of a horse with ID is recommended.

Hay

There is currently limited research on optimal hay feeding guidelines for ID horses. However, feeding preserved forages (such as pellets and cubes) to these horses is a common practice, whether on their own or mixed with a commercial concentrate.

A 2024 study investigated the insulinemic responses to three different forage pellets — timothy, alfalfa, and timothy-alfalfa — when fed at a rate of 1 g/kg BW. The NSC content of the pellets ranged from 9.8-10 percent on a DMB.

Based on the data, the authors concluded that the ID horses lacked an augmented insulinemic response to low NSC forage pellets (fed in small amounts), which indicates that they could be a safe feed product for ID horses.⁵

More research is required to fully understand safe guidelines for the NSC content of hay.

Pasture

There are numerous studies that have examined insulinemic responses of ID equines to pasture forage.

When grazing pasture grass with 6 and 10.9 percent NSC, both the moderately ID and severely ID ponies had significantly higher insulin responses compared to the healthy ponies.⁶

Another study that measured metabolic responses in ID horses directly off pasture forage with NSC levels ranging from 7.3-12.4 percent showed they were higher in all seasons compared to healthy horses.⁷Based on these studies, it is recommended to limit fresh forage availability for ID horses.

Other management tactics to reduce the risk of EL developing in ID horses on pasture are to restrict grazing times to when NSC content is lower (such as early morning hours) and implement a grazing muzzle to reduce intake.⁸Research in healthy horses has shown that implementing a grazing muzzle can reduce pasture intake by about 30 percent.⁹

Slow Feeding

Although we are continually learning more with scientific advancements, there is still much we do not yet know about optimal management for metabolic horses. A challenge for many horse owners is that they do not have control over the forage their horse receives. In these cases, tools such as slow feeders are beneficial.

When feeding hay to horses, slow feeding tools are often recommended.

Research has shown that horses consume hay faster when it is fed loose on the ground rather than in a hay net.¹⁰Additionally, in a follow-up study, the authors showed that horses fed from the hay net had lower peak insulin concentrations compared to those fed loose hay on the ground.¹¹Currently, there is a lack of research on how horses with ID respond to various forage management strategies.

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When horses eat from a hay net, their hay consumption is slower and their peak insulin concentrations are lower than if fed hay on the ground. Photo: Doswell Creative

Benefits of slow feeding have also been demonstrated regarding concentrate feeds. In a study with metabolically healthy horses, a 26 percent NSC concentrate was fed in one of four ways: in a bucket, in a dish with a waffle base, in a bucket with balls inside, or with water. The dish with the waffle base and the bucket with balls inside extended the eating period. The authors found that the total postprandial insulin response was lower in both the slow feeding groups.¹²Although this study was done in healthy horses, it is hypothesized that ID horses might benefit from altered feed setups to reduce postprandial insulin responses.

In addition to slow feeding devices such as hay nets and waffle dishes, grazing muzzles can be used. Based on the current research, it is hypothesized that slow feeding devices are beneficial to ID horses and should be implemented as part of their management plan.

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A grazing muzzle can reduce a horse’s pasture intake by about 30 percent. Photo: Doswell Creative

New Guidelines Summary

Based on the most recent research, it is recommended to ensure that when feeding concentrates to ID horses, they do not exceed 0.1 g NSC/kg BW/meal. Many ID horses are overweight and only require a ration balancer to meet their nutritional requirements outside of the hay they consume. Also note that the NSC content of ration balancers can vary significantly. Therefore, it is recommended to ensure that the grams of NSC per kg BW per meal calculation is followed. Consult a qualified equine nutritionist if you need assistance with this calculation.

For ID horses that need to gain weight or do not maintain a healthy body condition on forage and a ration balancer, fat should be added for supplemental calories and the same NSC feed guideline should be followed. Oils are a great source of calories that do not cause an increase in blood insulin when fed.

Although there is less research on forage for ID horses, it is recommended that ID equids be fed hay that is less than 10 percent NSC on a DMB. If pasture access is given, these horses should be restricted with a grazing muzzle and/or shorter duration of turnout.

Remember, in order to know the NSC content of hay a laboratory analysis must be done.

Take Home Message

It is well known that when healthy horses and those with ID consume the same diet, the ID horses have elevated insulin responses, putting them at a higher risk of developing EL. The marketing of various feed products for metabolic horses varies significantly, and although products might be marketed for these horses, it does not mean that they are safe to feed or follow the most up-to-date scientific guidelines.

Taking the time to evaluate your horse’s feed and forage is critical to ensuring it is within the recommended safe guidelines. Remember, new research is continually becoming available, and our management tactics must change as we learn more to promote optimal health and well-being for our beloved horses.

Related: What Is Teff Hay for Horses?

More by Madeline Boast

Footnotes