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Obese – Laminitic – EMS – Cushing Diseased Horses

Complications of Equine Obesity

Overweight horse standing in lush knee high pastureAside from the obvious physical issues of too much condition affecting movement, respiratory stress, joints etc, the biggest issue on the horses physiology is the onset of metabolic problems from excess blood glucose and insulin: such as insulin resistance, laminitis, endocrine complications such as Cushing’s disease or Equine Metabolic Syndrome (EMS). The link between all of these is obesity, which is why it is vital to recognise the onset of too much condition and deal with it quickly. Adipose (fat) tissue is an active endocrine organ and when they are in excess they secrete body chemicals that impair insulin signalling within fat and muscle so that insulin resistance develops. Insulin is an anabolic hormone produced in the pancreas and is important in the regulation of fat metabolism. When a horse ingests glucose (from grass and carbohydrate feed), insulin is released to control the amount of glucose in order to maintain normal levels in the blood. With an overload of fat cells in the body, the natural control of glucose is reduced and hence insulin resistance begins. In horses, the particular condition is called compensated insulin resistance, a direct result of ingested carbohydrates and is not the same as the human condition of poor glucose control which occurs when the pancreas does not produce enough insulin and it becomes type 2 diabetes. Horses do not suffer from that. EMS is also a direct result from compensated insulin resistance.

Laminitis is a constant concern for overweight horses, more especially ponies, and can be an added complication with EMS or as a stand-alone result of high carbohydrate intake and overweight condition. Conversely a history of laminitis can predispose an animal to develop EMS when insulin resistance develops.

Horse with rough shaggy coat from cushings disease.

Horse with cushings disease

Cushing’s disease is known as pituitary pars intermedia dysfunction, shortened to PPID. As the names suggest it is a condition of the pituitary gland which produces a hormone known as ACTH. This in turn stimulates the adrenal gland to produce the hormone cortisol. When cortisol is not well controlled due to malfunction of the pituitary gland, the levels are elevated this in turn elevates blood sugar (glucose). So here again insulin resistance occurs as the levels of glucose are too high for the amount of available insulin. With PPID the high cortisol levels can develop from a tumour on the pituitary gland, or from prolonged stress which can be from many years and many factors. This is why it tends to develop in the older horse and a horse with PPID can become very overweight or underweight. The clue to this disease is the development of a very curly coat, starting with the legs.

Feeding starch to a horse with Cushing’s is also inappropriate because of the inherent insulin resistance. Testing for insulin resistance and diagnosis of EMS, Laminitis and Cushing’s Disease will need to be carried out by a veterinarian. All obese horses should be screened for EMS.

Basic Management

The link with the development from just being overweight to insulin resistance, EMS, Laminitis and onset of Cushings is the intake and digestion of starch, whether from carbohydrate feeds or sugars in the pasture and hay. The problem with overweight horses and ponies is that while they have health complications from their condition, it is counterproductive to actually starve them as that will create other negative complications will occur from that as well as impacting on the overall wellness and health of the horse, it is a slow process to reduce weight (don’t we humans know!). Starving a horse will create binge eating when he gets out to the paddock and that will cause a sharp rise in insulin.

Analysing that your horse is tending to be overweight and taking control at an early stage is vital. A horse that is carrying obvious fat on the body, pouches on the rump, ribs out of sight and hard to feel, wobbly crest on the neck is overweight.

How to Measure Body Condition:

Table 1. Characteristics of Individual Condition Scores

 1. Poor

Bone structure easily noticeable, animal extremely emaciated, no fatty tissue can be felt.

Bone structure easily noticeable.

Spinous processes project prominently.

Spinous processes project prominently.

Tailhead (pinbone) and hook bones project prominently.

Bone structure easily noticeable.

 2. Very Thin

Faintly discernable, animal emaciated.

Faintly discernable.

Slight fat covering over base of spinous processes. Transverse processes of lumbar vertebrae feel rounded. Spinous processes are prominent.

Tailhead prominent.

Slight fat cover over ribs. Ribs easily discernable.

Shoulder accentuated.

 3. Thin

Neck accentuated.

Withers accentuated.

Fat buildup halfway on spinous processes but easily discernable. Transverse processes cannot be felt.

Tailhead prominent but individual vertebrae cannot be visually identified. Hook bones appear rounded but are still easily discernable. Pin bones not distinguishable.

Slight fat cover over ribs. Ribs easily discernable.

Shoulder accentuated.

 4. Moderately Thin

Neck not obviously thin.

Withers not obviously thin.

Negative crease along back.

Prominence depends on conformation; fat can be felt. Hook bones not discernable.

Faint outline discernable.

Shoulder not obviously thin.

 5. Moderate

Neck blends smoothly into body.

Withers rounded over spino