To prevent equine metabolic syndrome (EMS) in aging horses—or at least severe disease associated with it— veterinarians must keep up to date on the condition and its risk factors and management tactics.
Doing so, they can better identify horses likely to develop EMS and test to confirm their suspicions or less outwardly obvious cases, said an equine endocrine specialist.
“Our understanding of and recommendations about equine metabolic syndrome and PPID (pituitary pars intermedia dysfunction) certainly are continuing to progress and develop,” said Katherine E. Wilson, DVM, MS, Dipl. ACVIM, a clinical associate professor of large animal internal medicine in the Virginia-Maryland College of Veterinary Medicine’s Department of Large Animal Clinical Sciences, in Blacksburg, Virginia, who described what vets need to know about EMS and PPID during the 2022 American Association of Equine Practitioners Convention, held Nov. 18 to 22 in San Antonio, Texas. “And so staying on top of all these endocrine diseases can be really important in practice.”
Recognizing the Equid At Risk for Metabolic Problems
Equine metabolic syndrome is perhaps best known for its link with the development of laminitis due to related insulin dysregulation (ID) and obesity. But Wilson said the syndrome can also lead to:
- Hyperlipemia (elevated fat concentrations in the bloodstream)
- Hyperglycemia (elevated blood glucose levels)
- Hypertriglyceridemia (elevated levels of triglycerides, which are a component of fat)
- Sheath and mammary edema (fluid swelling)
- Lipomas (fatty tumors)
- Inappropriate lactation
- Fertility issues
Prompt recognition is key to circumventing advanced disease processes that can be particularly challenging to treat, she said. “Our goal should really be to identify individuals that have early disease, subclinical disease in order to be able to prevent severe disease and the development of laminitis,” Wilson noted.
Typically, both genetic predisposition and environmental and management factors lead to the development of EMS.
Pony breeds, Arabians, Paso Finos, Andalusians, Tennessee Walking Horses, Morgans, Miniature Horses, and donkeys are the breeds that tend to develop EMS, said Wilson. They might have “thrifty” genes that make them easy keepers, capable of thriving on fewer calories than other equids of similar stature. While researchers are homing in on genes associated with hyperinsulinemia and laminitis, more studies are needed, she said.
But not all genetically predisposed equids develop EMS and, likewise, not all EMS cases appear to be based in genetics.
For example, an obese animal in this high-prevalence breed group is relatively easy for practitioners to identify as being at risk, Wilson said. “But animals at moderate risk can be a little bit trickier,” she explained. “These are animals that might have few genetic risk factors, but maybe not of a predisposed breed, that are allowed excessive caloric intake and limited exercise and other environmental risk factors.
“And the opposite is true, too,” she continued. “An animal that is at an increased genetic risk, like a donkey, (which gets) controlled caloric intake and regular exercise—although I don’t know a ton of donkeys that get a lot of controlled exercise—certainly might (still) be at increased risk as well.”
Age seems to play an important role—particularly relating to fat pockets, or adiposity, which is an important risk factor, Wilson said. Because adiposity increases naturally with age—because metabolism drops while appetite stays the same—older horses become clear candidates for EMS development. Plus, older horses and ponies are more likely to have higher insulin concentrations and lower leptin and adiponectin concentrations than younger ones, placing them at even greater risk of EMS and laminitis, she said.
Diagnosis involves testing basal and after-meal insulin levels as well as investigating hormone levels associated with PPID—a condition that frequently occurs along with EMS, especially in older horses.
While study results suggest the gut microbiota differs between EMS and non-EMS horses, it’s still too early to know what aspects to look for in the microbiota to diagnose EMS, she said.
Managing EMS Cases to Prevent Severe Disease
Metabolic horses need a controlled diet low in cereal grains and treats—including fruits and vegetables—and other nonstructural carbohydrates. The aim, Wilson said, is to maintain a lean to average body condition score while controlling ID.
To manage these horses optimally, owners must comply with veterinary recommendations, she added, which often doesn’t happen.
“A lot of the time, until the animal has laminitis, owners don’t get very proactive about trying to institute some of these management changes because they don’t understand the severity of the disease,” Wilson said. “So having us come in regularly to check these animals to make sure that they are on track can be something that we can utilize in practice.”
Overweight EMS horses need restricted diets, consuming 1.5% of their body weight in dry matter intake (DMI), unless they are among those equids experiencing weight-loss resistance that might need a DMI of around 25% less than that. The goal is to reduce weight by 0.5% to 1.25% of the initial body weight per week, Wilson said. Laboratory analyses of forage provide information critical to understanding the calories and nutrients these animals are receiving.
Senior horses might struggle with their weight and insulin due to changing metabolism, gastrointestinal malabsorption of nutrients, PPID, and dental disease, she added. These horses should get their energy primarily from fats, such as vegetable oil, instead of starches.
While exercise appears to improve insulin regulation in humans, it’s still unclear whether it helps in horses, said Wilson. The current recommendation is to ensure sound at-risk horses get at least 30 minutes of moderate exercise per day, five days a week. Laminitic horses might be capable of working on soft ground with veterinary monitoring.
Even so, such exercise isn’t always feasible in these horses, she added.
“Moderate intensity exercise actually means a canter to a fast canter for 30 minutes,” Wilson said. “That’s a lot more exercise than many horses probably get five times a week … and low-intensity exercise actually means a fast trot to a canter. Again, that’s a lot of exercise, especially for some of these predisposed breeds and older horses who might have concurrent problems like osteoarthritis or some musculoskeletal injury that precludes them from being able to exercise, besides laminitis.”
Medications can complement changes in management when needed, said Wilson. Levothyroxine sodium can reduce body weight and improve insulin sensitivity in horses, and sodium-glucose cotransporter 2 (SGLT2) inhibitors can reduce insulin levels by inhibiting the reuptake of glucose in the kidneys.
The efficacy of drugs such as pioglitazone and metformin hydrochloride is still debated, but study results suggest they show promise in helping control EMS, she said.
No management program is complete without good monitoring using reliable, objective measurements such as body condition scoring, weight scales or tapes, and diagnostic testing, said Wilson.
“It’s very helpful to have baseline assessment of insulin dysregulation, so we have something to compare to while we’re initiating these management changes,” she said.