Fat ponies and equine metabolic syndrome

Many horsemen and women grew up with the idea that ponies should look like “Thelwell ponies” ~ round and fat. However, studies show that a fat pony might be an unhealthy pony.

If most of the fat is laid down in the abdomen and the pony shows a tendency to have laminitis, the pony might have a condition called Equine Metabolic Syndrome (EMS).

The fat in the abdominal area is called omental fat and it has been found to produce hormones.  These help regulate a number of body processes and are programmed towards enhancing ponies’ ability to survive long cold hungry winters.

The fat also produces cortisol, a steroid that inhibits the action of insulin, so high cortisol levels result in insulin resistance and a degree of hyperglycaemia (high blood sugar levels).

In the wild, ponies are programmed to put on weight during summer and autumn when there is plenty of pasture, and fat is laid down. As the pony gradually loses weight during the winter, the level of omental fat reduces and the state of insulin resistance becomes reversed.

However, in a domestic environment ponies are fed grain-based feeds year-round, or even just hay and other forages, so they don’t lose weight over winter.

This means their insulin resistance is not reversed, and so they are vulnerable in spring when the sweet new grass comes up, because their high levels of cortisol and sugar increase the risk of laminitis developing. The horse cannot properly metabolize carbohydrates, including starches and sugars. Laminitis is a painful inflammatory condition of the tissues (laminae) that bond the hoof wall to the pedal (coffin) bone in the horses hoof. (The historical name for laminitis was “Monday morning sickness” as it was first identified among urban working horses pulling, for example, coal carts. Such horses would work hard on weekdays, but would spend the weekend “resting” immobile in their stables while receiving full rations, with the result that they would manifest painful lameness on Monday morning when required to return to work.)

Common signs of EMS are:

  •  Obesity in adult ponies or horses (although a minority may be normal-sized);
  •  A “good doer” who puts on weight easily and loses it with great difficulty;
  •  A horse that is ravenously hungry all the time;
  •  Urinating frequently;
  •  Lethargy and laziness;
  •  Infertility or abnormal cycles in mares;
  •  Abnormal body fat distribution, eg, thickened, cresty neck; excess fat around head of tail; fatty shoulders; flabby, fatty sheath; pot-bellied look.

To prevent EMS, firstly control the pony’s diet. Reduce calorie intake and eliminate simple sugars (carbohydrates).

Mature ponies that are in ideal body condition and in light work may need little more than good quality pasture or hay and possibly a complete vitamin and mineral supplement.  This ration though simple, is low in starch, and this is an important step in avoiding equine metabolic syndrome.

There are also feeds available that are grain free and have been formulated for horses with this sort of condition. Ask the feed supplier for examples.

Do not feed carrots, apples or sweet feeds.

Some research has shown that soaking grass hays in warm water for an hour and half before feeding can reduce the non-structural carbohydrate concentration of the hay by as much as 40%.

Even if the hay is soaked for a shorter time, or in cold water, there is still some reduction of non-structural carbohydrates because they are water soluble. Soaked hay should be fed immediately to prevent mould formation.

Supplements containing antioxidants, chromium and magnesium claim to be of help (possibly by increasing insulin sensitivity), but the research is not yet conclusive. Veterinarians may have an opinion on this.

Exercise is also essential as it encourages a loss in omental fat, and it also promotes an increase in glucose uptake.  A fit pony (even if slightly overweight) has increased sensitivity to insulin and will lose weight faster than an unfit pony.

The exercise must be tailored to the abilities of the animal.  Vigorous exercise is obviously not sensible for very old or stiff animals or those that already have laminitis. Nevertheless, if the pony cannot be ridden because of the school or extramural commitments of the rider, a few minutes on a lunge-rein in either direction at a gentle trot, or a walk out on a lead-rein by a groom for half an hour will, if done regularly, do the trick.

If laminitis develops exercise may not be possible and this presents difficulties in management. It is therefore worth being proactive and tackling the condition before laminitis occurs.


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