Do you ever wonder why is it that some horses need extra good quality hay, grain and a blanket just to make it through the winter, and others merely have to look at hay and they get over conditioned?

We call these horses “easy keepers”. One theory is that they kept their “thrifty genes” – in nature, wild horses survive on minimal calories. They not only have to travel to seek nourishment but they are digging and searching for very tiny amounts of poor-quality food for much of the winter. Being able to store energy in the way of fat deposits is beneficial to helping them survive these times of food scarcity.

These days, horses get more than enough feed, with at times (depending on the season and their owners free time) very little asked of them in the exercise department.

Today we are going to touch on two common endocrine disorders (disorders of hormone production) we see in horses where we observe abnormal fat stores, lameness, lackluster energy and many other signs. These are Equine Metabolic Syndrome and Pituitary Pars Intermedia Dysfunction (PPID) aka Equine Cushing’s Disease.

Equine Metabolic Syndrome (EMS)     

Equine Metabolic Syndrome (EMS) is defined as a condition where the horse is overweight, insulin resistant and subsequently much more prone to laminitic episodes. Laminitis is extremely painful and can be the precursor to founder. There are a few disease conditions that classically cause laminitis in all horse breeds. These include retained placenta, grain overload, sepsis etc. The laminitis we see in horses with metabolic/endocrine disorders comes without the presence of these disease conditions and therefore is a classical sign that often leads us to the diagnosis of EMS.

With EMS, horses are prone to obesity, and abnormal fat deposits. Breeds that are genetically predisposed are Pony and Miniature breeds, Morgan’s, Andalusians, Warmbloods, Paso Fino’s and Saddlebreds. If a horse takes in more calories than it is expending, the excess sugar intake is stored in the form of fat deposits. These fat deposits often show up as cresty necks and fat pads at the shoulders and tail base.  In horses with EMS, their tissues are less sensitive to insulin (a hormone) for a few reasons – these are: genetics, diet type, age, sex, and even fat itself releases hormones that inhibit insulin. Eventually the body ramps up its insulin production to attempt to move glucose into the cells so it can be used for energy. The lack of sugar being moved into the cells by insulin leads to a hungry horse and the cycle continues. It should be noted however that not all horses with EMS have to be obese to have these problems – they can be a good body condition and still have hyperinsulinemia (high blood insulin) which is the main cause for the outward problems we see.

The usual onset of this disease is 5-15 years. When EMS is suspected, we measure a horse’s insulin, glucose, thyroid and ACTH levels. Hypothyroidism is often a secondary metabolic condition that can complicate EMS management, and ACTH levels assess the horse for Equine Cushing’s Disease.

The treatment for EMS once diagnosed is aggressive weight loss and management of laminitis where necessary.  It is usually recommended to feed the horse 1.5% of its body weight instead of the usual 2% as a baseline.  EMS horses are also recommended to have a diet of <10% non-structural carbohydrates (NSC).  To ensure this level of sugars in the feed is appropriate, a person can have their hay tested. If you need to decrease the NSC of hay you already have you can also soak the hay, usually 60 minutes in cold water which works quite good at reducing NSC (though not always practical in Manitoba winters). Cutting out grains or choosing complete feeds with <10% NSC are also useful. In warm months pasture grazing should be completely stopped OR limited to night time and early morning if necessary, until the appropriate weight is reached – even then, some horses cannot return to pasture turnout. In some cases, grazing muzzle are used to slow down the horse’s intake.

Exercise can be started if the horse is not laminitic and can help improve insulin sensitivity. Laminitis can be ruled out during the physical exam plus/minus radiographs if there is need. If laminitis is active then based on severity a horse is placed on stall rest or in a small pen in deep bedding or with padded shoes like soft rides. Appropriate pain control is also implemented. Most importantly, a farrier should be involved as soon as possible to properly balance the hoof and reduce tension on tendons that attach to the coffin bone, reducing founder risk.

Depending on the severity, if there is a lack of response to diet change, there are some medical therapies available to help improve insulin sensitivity and weight loss. One of these is Levothyroxine. By inducing a mild hyperthyroid state the body’s metabolism is ramped up to expedite weight loss. Levothyroxine also helps improve tissue insulin sensitivity. This would be used as a temporary aid for weight loss, or longer term if they are concurrently hypothyroid.

There are also many supplements which may be of benefit but unfortunately have yet to be scientifically backed.

We measure treatment success based on weight management, reduced laminitis episodes and insulin testing.

Equine Cushing’s disease – Pituitary Pars Intermedia Dysfunction (PPID)

Equine Cushing’s or Pituitary Pars Intermedia Dysfunction (PPID) is the enlargement of the pars intermedia; a part of the pituitary gland in the brain, which results in the overproduction of hormones – primarily ACTH (adrenocorticotropin hormone). This leads to abnormally high cortisol levels in the horse which affects numerous functions in the body.

Signs we see in horses include long haircoat or failure to shed their winter coat, poor immune system, hoof abscesses, excessive sweating, loss of muscle mass (particular the topline), infertility, pot belly, low energy, and in some cases excess drinking and urinating. These horses may also develop laminitis.

PPID is more often seen in horses >15 years old.  Horses showing signs suspicious of PPID are tested using resting ACTH levels as well as often testing for insulin and glucose levels as well. Unfortunately horses can have both EMS and PPID but a horse with EMS is not guaranteed to have PPID down the road. More advanced testing is available for horses whose initial results are inconclusive. One important thing to note is that these hormones also have natural seasonal fluctuations. ACTH has a fall fluctuation where it will increase temporarily in all horses.

Thankfully there is a medication for managing PPID called Pergolide. This is a daily medication. It slows the progression of PPID and improves the clinical signs but it unfortunately is not a cure. Horses can do well on treatment for many years.

Diet requirements are based on their body condition and can be adjusted to meet each horse’s needs. If insulin resistance is concurrent, then similar diet changes are done as for EMS. If the horse is not overweight, does not have hyperinsulinemia, and is losing muscle a senior feed and good quality hay may be more appropriate.

All in all, an annual vet check will help us to recognize early indicators and recommend testing where necessary, but here are some things you, as horse owners, can be on the look-out for:

Signs of PPID

  • Long hair-coat /failure to or slow shedding of winter coat

  • Muscle mass loss – especially over their back (topline)

  • Low energy / Poor performance

  • Infertility

  • Prone to lameness – solar abscesses, laminitis

  • Prone to infections

  • Increased drinking and urinating

  • Pot belly

  • Increased sweating

Signs of EMS

  • Obesity – Cresty neck

  • Laminitis

  • Widened white line

  • Repeat episodes of hoof abscesses

  • Divergent hoof rings – wavy lines across the hoof

  • Infertility

Written by Dr. Heidi Bjornson
Learn more about Dr. Heidi Bjornson here.