Essential pet advice with vet Jo Gourlay

Share this article

Having tackled Pars Pituitary Intermedia Dysfunction (PPID), which incorporates Equines Cushing’s disease, last week, we now look at a similar condition often compared to type II diabetes in people – Equine Metabolic Syndrome (EMS).

In contrast to PPID, EMS typically occurs in young to middle-aged horses not old animals, although obese native ponies are again over represented. Another similarity is a history of recurrent bouts of unexplained laminitis occurring where, despite every effort, the pony has “got fat on fresh air” or is just generally seen as a very “good doer”.

The laminitis may be very subtle so no lameness is detected, only the farrier commenting on distortions in the hoof growth pattern. Fat deposits on the crest of the neck, shoulders, base of the tail and around the mammary gland in mares or sheath in geldings are also common. Other signs of EMS include poor fertility, and increased hunger, lethargy and increased urination.

It’s been suggested the condition is a result of evolutionary developments to help native ponies survive harsh winters. During the spring and summer when lush grass in plentiful, weight is piled on in the form of fat both externally visible and also in the tissue around the guts. These fat cells have additional roles to being a reserve energy store such as releasing certain hormones involved in regulating the body, which is how they help them survive the winter months.

One of the hormones released, through various steps, stops the action of insulin (a hormone that controls the blood glucose level). The long-term consequence of this is something called insulin resistance which is where the horse starts to lose the ability to respond correctly to insulin, and ends up producing more and more of it. The net result is elevated insulin and glucose levels in the blood.

This is beneficial to a fat pony going into a harsh winter as the glucose is kept ready for essential areas such as the brain. Over the following few winter months the fat deposits reduce and the whole process is reversed, leaving a lean but healthy pony ready to gain weight from for the next lot of lush spring grass. The problem occurs when domesticated ponies never get lean over the winter, or are so obese in the autumn the weight never really dips enough for the state of insulin resistance ever to become reversed.

Diagnosis of the condition relies on eliminating other similar conditions like PPID or other hormonal problems such as thyroid dysfunctions (although it’s not unusual for 
a horse to have EMS in 
addition to these). The history alongside elevated glucose and insulin levels is highly suggestive of EMS.

Management of EMS requires control of both diet and exercise. Although it seems harsh, a very strict diet of, ideally, soaked hay with additional vitamins and minerals must be adhered to with no hard feed and limited or no access to grass. The hay should be weighed and a ration worked out with guidance from your vet based on the horse’s ideal body weight (not their current one) so gradual weight loss is achieved (sudden weight loss can be detrimental).

Once any laminitis issues are dealt with, a regular exercise routine should be put into place not only to aid the weight coming off but also because it’s known to increase the glucose uptake and increase insulin sensitivity again.