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Equine - Metabolic Syndrome



Equine Metabolic Syndrome (EMS) is seen in overweight horses and ponies and is sometimes associated with laminitis. The disease process is similar to Type 2 Diabetes in humans. Excessive fat cells decrease the body’s sensitivity to insulin (insulin resistance), causing higher levels of circulating insulin. This alters the blood flow in the feet which, with other compounding factors, can cause laminitis.

Native breeds are most at risk of developing EMS but it also occurs in others, probably because we look after our horses too well by offering good roughage with high quality feed and by rugging them up to protect from harsh weather. Not all overweight horses develop EMS but all EMS horses are overweight, so weight control is essential to prevent it developing.

Clinical signs

Horses running the risk of developing EMS are overweight. They may be "cresty" over the neck, have bulging fat pads above the eyes, fatty accumulation over the shoulders and a love heart shaped rump.


At risk horses are identifiable by an excessive body condition score and the presence of fat pads. Laboratory testing can be used to diagnose insulin resistance by measuring blood insulin and glucose levels. The blood test must be done after a 6 hour/overnight fast. If the results are inconclusive or there is still a suspicion of insulin resistance, insulin and glucose can be measured after a glucose challenge. Mild insulin resistance can also occur with PPID (Equine Cushing's Disease). This should be ruled out before treatment for EMS, as it is also a risk factor for laminitis.


The aims of treatment are weight loss and increasing the body’s sensitivity to insulin.

Dietary modifications:

-Stop hard feed. Most horses do not need much hard feed; a suitable feed balancer may advised to ensure the nutritional requirements are met

-Soak hay – ideally, hay should be soaked for 2 hours and rinsed thoroughly before being fed. This will decrease water soluble carbohydrates (sugars) in the hay. If hay is soaked for too long, fibre content, which is important to maintain healthy gut motility, can be decreased.  Hay should be fed immediately after being rinsed to prevent mould growth.  Haylage is unsuitable for soaking due to fermentation processes.

-Hay nets with small holes can be useful to slow the rate of hay intake and make it last longer.


-If the animal is not currently affected by laminitis, regular exercising is the best way to fight obesity and its associated issues. Exercise increases the body’s sensitivity to insulin and mobilises fat cells for energy. 

-The exercise program should be carefully thought out, especially with any horse at risk from developing laminitis, or particularly unfit individuals. Exercise should be regular but gentle at first, in accordance with the horse’s level of fitness.

Monitor weight

-Weigh tapes – these are readily available and easy to use but are not always very accurate!  They are very useful for monitoring for weight loss and for keeping up morale!

-Weigh bridges – a lot of feed companies now have mobile weigh bridges and will do free yard visits if they have enough horses to see.

-Horses should naturally lose weight through the winter and gain a small amount through the summer. If your horse’s weight is a concern, the winter can be a good time to encourage steady weight loss, as you have more control over roughage intake. Haylage should be avoided, as should 'over-rugging'.


-For confirmed cases of insulin resistance and particularly for horses with acute laminitis where rapid weight loss and correction of insulin resistance is required, medication may be discussed. Metformin is a human drug used to treat Type 2 Diabetes in humans but unfortunately it has quite a low bioavailability in horses (~8%).