Researchers Examining Weight Gain
Obese horses and ponies should have limited access to pasture while on a weight loss plan. | Christ M. West

Many horses in the U.S. are obese or overweight, and some horse owners view this condition as acceptable or even desirable, making it difficult for veterinarians to discuss the topic honestly with their clients. As a result, obese horses are now at risk of “obesity-related laminitis,” synonymous with hyperinsulinemia-associated laminitis (HAL), which currently poses one of the greatest threats to equine welfare and, yet, is largely preventable, said David Rendle, BVSc, MVM, CertEM (IntMed), Dipl. ECEIM, FRCVS, during his presentation at the 2023 Saratoga Vet & Farrier Conference, held Sept. 27-30 in New York.

“Among the many reasons that veterinarians fail to discuss obesity is fear of offending the client,” said Rendle. “Thus, instead of discussing the horse’s condition directly, demonstrating hyperinsulinemia can be a powerful stimulus for management change. This type of conversation might be more comfortable and could ultimately have the same endpoint: dietary change and weight loss.”

Recent studies performed in the U.K. have shown the risk of laminitis in ponies doubles if Insulin concentrations exceed 20 U/L when fed a pasture/forage diet. “These insulin levels are much lower than we worried about previously, so we really have to do much, much more to control hyperinsulinemia,” said Rendle. This information can be used to help clients understand the dangers of obesity in their horses. 

Rendle recommended veterinarians work with their clients to employ a three-pronged approach to controlling obesity and hyperinsulinemia involving diet, exercise, and, in some cases, medication.

Restricting Obese Horse and Pony Diets

Dietary restriction includes removing cereal feeds and treats from the horse’s diet, said Rendle, but to lose weight most horses will need to consume only 1.5% of their body weight in dry matter per day. “For most owners this seems like a shockingly small amount of forage,” he added.

In addition to limiting feed intake, owners should limit their horse’s time on pasture—even short periods of turnout can undermine weight-loss programs, said Rendle. “Under certain conditions, the nonstructural carbohydrates in grass can exceed 30%, which is comparable to many cereal-based feeds.”

Restricting a horse’s hay to 1.75% of body weight (17.5 lb for an average 1,000-lb horse) per day of soaked hay (to remove some of the water-soluble carbohydrates) is a good starting point, but additional restriction might be needed depending on the individual horse’s response. If the animal appears resistant to weight loss, Rendle said restricting feed further or adding in medication will likely be warranted.

In many cases when soaking and restricting horses’ hay you’ll need to add a low-calorie protein and mineral balancer to meet their nutritional needs.

How to Exercise Obese Horses:

Nonlaminitic Horses with insulin dysregulation (ID):

  • Minimum recommendation: Exercise at a low to moderate intensity.
  • Work horses at a canter to fast canter, ridden or unridden, or to a target heart rate of 130 to 170 beats per minute.
  • Work horses at least 30 minutes, five or more times per week.

Previously laminitic horses with recovered and stable hoof lamellae:

  • Minimum recommendation: Exercise at a low intensity on a soft surface (such as arena footing).
  • Work horses in a fast trot to canter, unridden, to achieve a target heart rate of 110 to 150 beats per minute.
  • Work horses more than 30 minutes three or more times per week.
  • Carefully monitor for signs of lameness.

General Tips:

  • Buddy up—this increases compliance/success by 45%
  • Make it fun and interesting—find new places to ride or join group rides. 
  • Set goals—use an online GPS activity monitor to track your progress.

Exercise Regimens for Obese Horses and Ponies

Exercise improves insulin sensitivity independent of the additional benefits of weight loss. You should continue to exercise horses with insulin dysregulation (an abnormal insulin response to sugar intake) even after achieving the desired body weight/body condition score.

“Exercise without dietary restriction won’t effectively improve an animals’ body weight, and exercise should only be recommended to horses and ponies not currently affected by laminitis,” added Rendle.

Medication for Horses With Obesity

Diet and exercise will always be the first two steps for achieving an appropriate body condition and insulin levels, but a horse might need medication when more rapid weight loss is necessary. For example, when veterinarians perceive the risk of laminitis or other obesity-related health issues to be high, or if the horse is actively suffering with laminitis, medication is likely necessary.

Medications that veterinarians might choose for these horses include levothyroxine or metformin; however, Rendle said, the sodium-glucose co-transport-2 inhibitors (SGLT2i) are increasingly popular and appear highly effective for improving hyperinsulinemia and promoting significant weight loss.

“Use the SLGT2is for as short a time as necessary to reduce insulin levels and body weight before being withdrawing the medication gradually over a few weeks,” said Rendle. “There are potential side effects such as hyperlipidemia (an excess of lipids in the bloodstream), and horses need to be monitored carefully as some can lose weight too rapidly.”

Take-Home Message

“Because conversations surrounding obesity can be challenging, demonstrating hyperinsulinemia may be more comfortable for a lot of veterinarians and can be a more powerful motivator for owners to embrace diet and management changes to decrease the risk of laminitis,”said Rendle. Veterinarians should help horse owners develop a dietary and exercise management plan for obese or overweight animals and continually monitor them to determine if medical management is necessary.