Pituitary Pars Intermedia Dysfunction (PPID) is an endocrine-related disease that commonly affects older horses of all breeds. Twenty percent of senior horses, ponies, and donkeys are believed to have PPID.

The condition results in an overproduction of pituitary hormones, causing metabolic dysfunction. Horses with PPID may also have insulin resistance and an increased risk of laminitis.

Typical clinical symptoms of PPID include abnormal coat condition with delayed shedding, muscle loss, impaired immune function, and behavioural changes.

PPID is diagnosed by your veterinarian with tests and observation of clinical symptoms. Pergolide mesylate (Prascend) is the only medication licensed for the treatment of the disease.

Appropriate management of horses with PPID involves diet, exercise, regular veterinary care, and consistent monitoring of hormone levels. If your horse has PPID, submit their diet online for a free evaluation by our equine nutritionists.

What is PPID?

Pituitary Pars Intermedia Dysfunction is a common equine endocrine disorder, primarily afflicting horses over the age of 15, and becoming more likely to develop as the horse ages. [1]

It involves an excessive production of hormones, such as adrenocorticotrophic hormone (ACTH), from the pars intermedia lobe of the pituitary gland located at the base of the brain.

The level of hormones in the pars intermedia of a horse with PPID can be 100 times higher than in a healthy horse.

The overproduction of hormones is caused by degeneration of the dopamine-producing neurons in the hypothalamus, potentially due to oxidative stress. Low dopamine levels impair the normal regulatory function that shuts off the production of pituitary hormones.

PPID is an age-related disease; aging is the only major risk factor for the condition, although horses as young as 7 years of age have been diagnosed. Breed and sex do not predispose horses to develop the disease.

Epidemiologic studies estimate that 20% of horses over the age of 20 are affected by PPID, and 30% of those over 30 are affected. [3]

Although previously referred to as Equine Cushing’s Disease, this title is now considered inaccurate. Cushing’s Disease in humans affects a different location within the pituitary gland. [2]

How Does PPID Affect Horses?

The equine pituitary gland consists of 3 lobes including the pars distalis, pars intermedia, and pars nervosa. PPID affects the pars intermedia part of the gland.

The hypothalamus, a part of the brain, controls the release of hormones from the pituitary gland. This gland plays a key role in regulating hormones related to metabolism and affects the function of various organs.

PPID results in an overproduction of multiple hormones that cause an abnormal metabolic state. Increased levels of these hormones affect various processes throughout the body.

In healthy horses, the neurotransmitter dopamine is released by the hypothalamus to inhibit the production of hormones by the pars intermedia. Dopamine binds to receptors on the surface of cells to turn off the secretion of hormones from this part of the pituitary gland.

PPID results from the degeneration of dopamine-producing neurons in the hypothalamus. This prevents the hypothalamus from regulating the release of hormones by the pituitary gland, such as adrenocorticotrophic hormone (ACTH).

Horses with PPID have high levels of circulating ACTH, triggering the adrenal gland to increase production of the stress hormone cortisol. Higher cortisol levels lead to insulin resistance.

Low dopamine also causes the pituitary gland to increase in size as the cells of the pars intermedia divide and enlarge. Horses with PPID may develop benign tumours in this part of the gland.

The expansion of the pars intermedia can cause other lobes of the pituitary and the hypothalamus to become compressed. This may cause a loss of function in these structures and result in a range of clinical symptoms.

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