PPID (Pituitary Pars Intermedia Dysfunction) / Cushing’s Syndrome

PPID, also known as Cushing’s syndrome, is a common endocrine disorder in middle-aged to older horses. It typically occurs from approximately 15 years of age onwards and shows no clear sex or breed predisposition. The disease develops as a result of dysfunction of the pituitary gland, which physiologically plays a key role in regulating the body’s cortisol secretion. In horses affected by PPID, this regulatory mechanism is disrupted, leading to excessive and poorly controlled cortisol release. Early clinical signs may include reduced performance, muscle atrophy, increased sweating, and impaired immune function. In advanced stages, delayed or incomplete shedding of the winter coat, increased water intake and urination (polydipsia and polyuria), laminitis, and insulin dysregulation (ID) may occur.

Diagnosis is primarily based on blood tests, which are particularly useful for identifying early cases. Initial clinical signs can be nonspecific; however, a simple blood test measuring adrenocorticotropic hormone (ACTH) concentration can support the diagnosis. If results are borderline, a thyrotropin-releasing hormone (TRH) stimulation test is recommended for more accurate assessment. For determination of the basal ACTH concentration, the horse may have eaten beforehand (excluding concentrate feed), and blood sampling can be performed at any time of day. However, due to circadian and seasonal fluctuations in ACTH levels, early morning sampling is recommended. For the TRH stimulation test, it is essential that the horse is fasted and that sampling is performed in the morning, preferably between January and June. For both tests, stress factors such as pain, acute laminitis, transport, or illness should be avoided prior to sampling, as they may interfere with test results.

If PPID is diagnosed, medical treatment with pergolide is recommended. This medication can significantly alleviate clinical signs and improve quality of life. Regular follow-up examinations are important to determine the optimal dosage for each individual horse. In addition, appropriate adjustments in feeding and management are essential to meet the increased needs of affected horses.

Equine Metabolic Syndrome (EMS) / Insulin Dysregulation (ID) / Insulin Resistance (IR)

In addition to PPID, equine metabolic syndrome (EMS) is another important metabolic disorder in horses. Approximately 30% of horses affected by PPID also exhibit insulin dysregulation or insulin resistance. These conditions reflect disturbances in carbohydrate and lipid metabolism and represent major risk factors for endocrinopathic laminitis.

Horses with EMS typically show regional or generalized obesity. Regional adiposity, particularly along the mane crest (“cresty neck”), shoulders, and croup, is a characteristic clinical sign and is often accompanied by increased appetite, laminitis, and occasionally colic. Easy-keeping breeds, such as ponies and hardy native breeds, are more commonly affected. Long-term overfeeding combined with insufficient exercise contributes significantly to the development of EMS, particularly in middle-aged to older horses.

Diagnosis may involve a simple blood test or dynamic testing to assess insulin regulation. For basal blood testing, the horse should not have received concentrate feed or access to pasture for 4–6 hours prior to sampling; hay intake is permitted.

Key components of treatment include weight reduction and increased physical activity. Feeding analysis and nutritional counselling can be arranged to ensure an adequate supply of essential nutrients while reducing overall caloric intake. Regular physical exercise is crucial in reducing the risk of laminitis. In therapy-resistant cases, pharmacological support may be used temporarily to improve insulin regulation and facilitate weight loss.