Insulin resistance, insulin dysfunction and equine metabolic syndrome are among a collection of rapidly increasing endocrine conditions affecting the horse population in the United States today.

Insulin resistance (IR) occurs when cells become resistant to the action of the insulin secreted by the horse’s pancreas, leading to higher blood glucose levels. The glucose secretion is the body’s attempt to lower blood glucose, thereby causing increased blood insulin levels. Some of the excess blood glucose is stored as glycogen in muscle and liver or converted to adipose tissue. Excess blood glucose is also excreted by the kidneys into the urine.

Insulin dysregulation occurs in horses that cannot regulate blood insulin levels. Equine metabolic syndrome often results from insulin-related dysfunction in horses and is characterized by three components: insulin dysregulation, observable obesity or localized fat deposits, and a high risk of or a documented instance of laminitis.

Farrier Takeaways

  • Insulin-resistant horses are overweight or obese with a body condition score greater than six. They can have abnormal fat deposits along the neck crest, tail head, sheath and mammary gland.
  • The ideal diet for an insulin-resistant horse should be forage-based and low in sugar.
  • One in five horse owners has never heard of insulin resistance or equine metabolic syndrome.

With an estimated 50% of the United States horse population overweight,1 managing insulin-related pathologies is a growing concern among horse owners and equine professionals alike. Fortunately, recognizing key indicators of IR, educating horse owners and implementing effective management techniques can decrease the risk of laminitis in affected horses, Mike Barker of Life Data Labs told attendees during a How-To Hoof-Care Clinic at the 20th annual International Hoof-Care Summit in Cincinnati, Ohio.

Identifying Insulin Resistance

Although grossly underdiagnosed, IR horses often share physical characteristics that make them readily identifiable.

“Most, but not all, insulin-resistant horses are going to be overweight or obese, with a body condition score greater than six,” Barker explains. “They may have abnormal fat deposits along the neck crest, tail head, sheath and mammary gland, and may have also internal fat stores.”

In addition to a high body condition score, Barker says IR horses are often described as easy keepers that have difficulty losing weight.

“These horses may be anywhere from 5-15 years old,” he says, “and often present with increased water consumption and urination, a loss of stamina and muscle tone, abdominal bloating, excessive hunger, and a tendency toward bouts of laminitis.”

IR can occur in any breed of horse, but is more likely in Andalusians, Arabians, mules, mustangs, Paso Finos, ponies, Quarter Horses, Saddlebreds and Tennessee Walking Horses, Barker says. Once risk has been identified, he advises consulting a veterinarian for testing options and a confirmed diagnosis.

Inside the IR Horse

Anytime a horse consumes pasture, hay, or commercial feed, the intestines absorb glucose — also known as blood sugar — into the bloodstream. In response to the increased blood glucose, Barker says the pancreas secretes insulin.

Insulin-Resistant-Horses

Most insulin-resistant horses are overweight or obese, with a body condition score greater than six. They can have abnormal fat deposits along the neck crest, tail head, sheath and mammary gland. Photo: Life Data Labs

“Insulin serves as a key,” Barker says. “It opens the gate within the cell or tissue and allows glucose to pass out of the bloodstream and into the tissue. If a horse is consuming excessive amounts of carbohydrates and sugar, that results in an excessive amount of insulin production and eventually, insulin resistance. In other words, the same amount of insulin doesn’t work as well as it did at one time.

“So, we have a rise in glucose, and the more glucose we have, the more insulin we have,” he continues. “The diet has created an overproduction of insulin within the horse.”

High levels of glucose and the resulting increase in insulin cause several problems for horses.

“First, they create an obesity problem,” Barker says. “This contributes to the regional fat pockets, like those found along the crest of the neck and the tail head. In obese horses, excess fat tissue contains high levels of [the cell-signaling molecules] adipokines, which contribute to inflammation and can ultimately increase the risk of laminitis. Two things are happening — the initial insulin resistance problem and the compounding problem of the adipokines.”

Adipokines are proteins produced by fatty tissue that can increase inflammation and further promote insulin resistance.

Managing IR

Managing an IR horse begins with diet.

“The first thing we need to do is reduce the horse’s weight,” Barker says. “The body condition score should be five or six at most. We need to focus on removing excess fat from the horse because that will also help reduce inflammation.”

The ideal diet for an insulin-resistant horse should be forage-based and low in sugar. Grazing muzzles may be used to reduce grass intake for horses on pasture while soaking hay for 30-60 minutes will help lower sugar content. Dry lots and slow feeders are also great tools. Above all, careful management is key, he says.


“One in five horse owners have never heard of insulin resistance…”


“Hay and feed should be analyzed to ensure horses are fed less than 10% non-structural carbohydrates,” he says. “We want to be continually monitoring the horse and limiting grazing and calorie intake.”

Veterinarian-prescribed medications and supplementation can also play vital roles in management. Barker recommends Farrier’s Formula Double Strength and its companion product IR Formula, both of which are manufactured by Life Data Labs.

“Farrier’s Formula Double Strength supports the overall quality of the foot,” he explains. “It’s been fed safely to hundreds of horses that have had laminitis or have foundered. The IR Formula is designed to be fed alongside our Farrier’s Formula — it helps improve the overall metabolism of the horse, thereby improving glucose metabolism and encouraging proper insulin action.”

Lowering Laminitis Risk

Endocrinopathic laminitis — laminitis that occurs in animals with an underlying endocrine disease such as insulin dysregulation or equine metabolic syndrome — is the most commonly occurring form of laminitis. Even so, Barker admits the correlation between the two is not well understood.

“There is a lot we don’t understand, but one thing is clear — we have more cases of this type of laminitis than any other type today,” Barker says.

There are several theories surrounding the link between underlying endocrine disease and laminitis.

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“One theory is that abnormal insulin levels may alter the function of the epidermal laminar cells of the hooves,” he explains. “We know there is excess inflammation, and it can result in vasoconstriction. Inflammation can also damage the endothelial cells. So, there are several possibilities, and we don’t know why the two occur together — we just know without a doubt that it happens.”

The importance of maintaining an appropriate body condition score through exercise to reduce the risk of endocrine-related laminitis is vital.

Educating Clients

Of all the steps farriers can take to help manage horses with IR, insulin dysfunction, or equine metabolic syndrome, Barker argues that educating clients may be the most important.

“A survey of horse owners pointed out the lack of knowledge,” Barker says. “One in five had never heard of insulin resistance or equine metabolic syndrome; one in three had never even researched the topic.2 These were people who defined themselves as experienced horse owners, not newcomers in the industry.

“As a farrier, you see these horses every 4-8 weeks,” he continues. “You’re dealing with them directly. Many owners don’t recognize [a horse with equine metabolic syndrome]. If you can help them identify a problem, you can help them prevent a future case of laminitis.”

Barker encourages farriers to be diligent about educating clients, assessing risk and monitoring progress.

“Many owners don’t understand the health conditions a horse may face if they don’t turn things around,” he says. “There are many undiagnosed, untreated horses — the guess is that somewhere between 20-25% of horses either have this issue or are on their way to developing it. If we can be proactive, we can help prevent the worst-case scenario in these horses.” 


References:

1. Thatcher CD, Pleasant RS, Geor RJ, et al. (2012) Prevalence of overconditioning in mature horses in Southwest Virginia during the summer. J Vet Intern Med 26, 1413-1418.

2. Golding E, Neavyn Neita A, Walshe N, Hanlon A, Mulcahy G, Duggan V. Survey of the knowledge and perceptions of horse owners in Ireland of common clinical conditions and their impact. Equine Vet J. 2023; 55(2): 270– 281. doi.org/10.1111/evj.13589.