Equine Metabolic Syndrome
(Insulin dysregulation syndrome, Equine syndrome X, Peripheral Cushing disease)

This is a condition commonly found in middle-aged horses (8-16 years) and ponies.

It is characterized by obesity, laminitis and insulin resistance. Increased fat deposition is commonly found around the neck and tail region.

Insulin resistance occurs when body tissues don’t respond to insulin released from the pancreas into the bloodstream. Insulin stimulates body cells to take-up glucose for energy production. This consequently causes an increase in blood insulin levels, a condition known as hyperinsulinemia.

Obesity has been identified as a major predisposing factor. Hyperinsulemia and high blood glucose levels cause constriction of blood vessels in the hoof leading to poor tissue blood perfusion, inflammation and consequently laminitis.

Affected horses are noted to have a ravenous appetite and don’t lose body condition even with a reduction in daily feed intake.

Not much is known about the cause of this syndrome but anecdotal research suggests it’s a genetic disorder.

It’s common among Saddlebred, Tennessee Walking, Paso Fino, Morgan, Mustang, and Quarter horses. Standardbreds and Thoroughbreds’ are rarely affected. No sex predisposition has been established (1).

Clinical signs
• Laminitis –usually slow in progress or history of recurrent episodes
• Colic
• Obesity with increased fat deposition around the tail and neck
• Insulin resistance

Obesity (a) is the main known risk factor for equine metabolic syndrome, and in horses, excess visible fat deposition occurs most commonly in the region of the neck crest (b) and rump (c) (2)

Management
There is no treatment protocol for affected horses rather the condition is managed through proper diet and exercise. This helps in weight loss and consequently increase insulin sensitivity (3).
a) Diet
This is aimed at reducing the daily calorie intake. Concentrates and high sugar treats should be avoided. Late mature hay or forage is usually recommended. To promote weight loss, affected horses should be fed hay at approximately 1.5% of their body weight in dry matter per day. If measuring is not possible, hay can be soaked in cold water for 30-60 minutes to reduce the amount of water-soluble sugars. Vitamins and minerals should be supplemented especially in cases where hay is soaked due to loss of macronutrients e.g. potassium, phosphorus. Horses not used to soaked hay can be fed chaff based feeds combined with a complete balancer (4).
Adlib pasture grazing should be restricted to avoid overfeeding. It’s preferable if horses are confined to paddocks for easier monitoring of feed intake or by use of a grazing muzzle.
b) Exercise
Exercise coupled with proper dietary restrictions results in weight loss and increased insulin sensitivity. Exercise should be initiated once affected horses show no sign of pain and are off anti-inflammatory medication. Exercise should entail approximately 15 minutes of trotting on soft level ground and progress steadily over time (2).
A veterinarian should be contacted if any of the above signs are observed for proper advice on a proper diet as well as administration of medication to ease insulin resistance and laminitis.

References
1. Kritchevsky JE. Overview of Equine Metabolic Syndrome. Available from: https://www.msdvetmanual.com/metabolic-disorders/equine-metabolic-syndrome/overview-of-equine-metabolic-syndrome
2. Morgan R, Keen J, Mcgowan C. Review Equine metabolic syndrome.
3. RA M, TW M, CM M. Prevalence and risk factors for hyperinsulinaemia in ponies in Queensland, Australia. Aust Vet J [Internet]. 2014;92(4):101–6. Available from: https://doi.org/10.1111/avj.12159
4. A. DAH, C. CG, A. HP, MC. AC. Assessment of body fat in the pony: Part I. Relationships between the anatomical distribution of adipose tissue, body composition and body condition. Equine Vet J [Internet]. 2011;43(5):552–61. Available from: https://doi.org/10.1111/j.2042-3306.2010.00330.x