Equine Endocrine Disorders: Diagnosis and Management

Equine endocrine disorders are a group of conditions that disrupt hormone regulation, metabolism, and energy balance in horses. The most common disorders include pituitary pars intermedia dysfunction (PPID, also called equine Cushing's disease), equine metabolic syndrome (EMS), insulin dysregulation, diabetes mellitus, and goiter. This article provides veterinarians, veterinary students, and horse owners with diagnostic and treatment guidance for these conditions, focusing on practical management decisions, diagnostic testing, and professional escalation criteria.

At a Glance

Understanding Equine Endocrine Disorders

Equine endocrine disorders involve dysfunction of the hypothalamic-pituitary axis, pancreas, thyroid, or other endocrine organs. These conditions often present with overlapping clinical signs, particularly laminitis, obesity, and metabolic disturbances. The Merck Veterinary Manual provides a comprehensive overview of endocrine diseases in horses, including diagnostic approaches and treatment options [4]. The American Association of Equine Practitioners (AAEP) offers resources for horse owners on recognizing and managing these conditions [1].

PPID is the most common endocrine disorder in older horses, while EMS is increasingly recognized in younger horses and ponies. Insulin dysregulation is a central feature of both conditions and is a primary risk factor for endocrinopathic laminitis. Diabetes mellitus is rare in horses but can occur secondary to PPID or pancreatic disease. Goiter is uncommon but may be seen in foals or horses with iodine imbalances.

Pituitary Pars Intermedia Dysfunction (PPID)

PPID, also known as equine Cushing's disease, is a progressive neurodegenerative disorder of the pituitary pars intermedia. It results in excessive production of proopiomelanocortin-derived peptides, including ACTH. The condition is most common in horses over 15 years of age but can occur in younger animals. The British Veterinary Journal published an early description of equine Cushing's disease, establishing the clinical and pathological features of the condition [6]. The Veterinary Clinics of North America: Equine Practice later provided a comprehensive update on the diagnosis and management of PPID [7].

Clinical Signs of PPID

The classic clinical signs of PPID include hirsutism (abnormally long, curly hair coat that fails to shed), delayed or incomplete shedding, laminitis, muscle wasting, lethargy, excessive sweating, polyuria, polydipsia, and recurrent infections. Affected horses may also develop a pot-bellied appearance, poor wound healing, and neurological signs such as ataxia or blindness. The Veterinary Clinics of North America: Equine Practice published a detailed review of pituitary pars intermedia dysfunction, emphasizing the clinical presentation and diagnostic challenges [8].

Diagnostic Testing for PPID

Diagnosis of PPID is based on clinical signs and endocrine testing. The baseline ACTH measurement is the most commonly used test. A single elevated ACTH concentration supports a diagnosis of PPID, but seasonal variation must be considered. ACTH levels are normally higher in the autumn, and reference ranges should be adjusted accordingly. The TRH stimulation test can be used to confirm PPID in horses with equivocal baseline ACTH results. The dexamethasone suppression test is an alternative but carries a risk of inducing laminitis in susceptible horses.

The International Journal of Molecular Sciences published a review of Cushing's disease across animal species, including horses, highlighting the translational insights for human medicine [9]. The Tijdschrift voor Diergeneeskunde provided an update on equine Cushing's disease, discussing diagnostic advances and treatment options [10].

Treatment of PPID

The primary treatment for PPID is pergolide mesylate, a dopamine agonist that suppresses ACTH secretion from the pituitary pars intermedia. Treatment is lifelong and requires regular monitoring of ACTH levels and clinical response. The British Homoeopathic Journal discussed a new approach to therapy in equine and canine patients with Cushing's disease, though conventional treatment with pergolide remains the standard of care [11].

Management of PPID also includes dietary modifications, regular hoof care, dental care, and parasite control. Horses with PPID are at increased risk of laminitis, infections, and other complications. Close monitoring and prompt treatment of intercurrent conditions are essential.

Equine Metabolic Syndrome (EMS)

Equine metabolic syndrome is a collection of clinical and metabolic abnormalities that increase the risk of laminitis. The core features of EMS include insulin dysregulation, obesity or regional adiposity, and a predisposition to laminitis. EMS is most commonly diagnosed in ponies, Morgan horses, Paso Finos, and other easy-keeper breeds, but can occur in any horse.

Pathophysiology of EMS

EMS is characterized by insulin dysregulation, which includes both insulin resistance (reduced tissue sensitivity to insulin) and hyperinsulinemia (excessive insulin secretion in response to glucose). Insulin dysregulation leads to impaired glucose uptake by tissues and increased fat deposition. The condition is associated with oxidative stress and inflammation, which further impair metabolic function.

Stem Cell Reviews and Reports published a study on in vitro generated equine hepatic-like progenitor cells as a novel cell pool for EMS treatment [12]. The research demonstrated that equine adipose-derived stem cells could be induced to differentiate into hepatic progenitor cells, offering a potential approach for restoring liver function in EMS-affected horses. The International Journal of Molecular Sciences published a study on orientin, a plant-derived flavonoid, which reversed premature senescence in equine adipose stromal cells affected by EMS through oxidative stress modulation [13]. These findings suggest that orientin may have therapeutic potential for restoring the regenerative capacity of adipose-derived stem cells in EMS horses.

Clinical Signs of EMS

The clinical signs of EMS include regional adiposity (cresty neck, fat pads over the ribs and tailhead, and omental fat), obesity, laminitis, and recurrent infections. Affected horses may have a body condition score of 7 or higher on a 9-point scale. The cresty neck score is a useful tool for assessing regional adiposity. Horses with EMS are at high risk of developing hyperinsulinemia-induced laminitis (HAL).

The Journal of Equine Veterinary Science published a case report of a mare with recurrent endocrinopathic laminitis linked to EMS [14]. The mare presented with severe laminitis refractory to treatment, despite dietary management and conventional therapy. An SGLT2 inhibitor was introduced to reduce resting insulin levels, but the horse ultimately required euthanasia. This case highlights the challenges of managing severe EMS and the need for continued research.

Diagnostic Testing for EMS

Diagnosis of EMS is based on clinical signs, morphometric measurements, and endocrine testing. Resting insulin and glucose concentrations are the initial screening tests. An elevated resting insulin concentration (>20 mIU/L) suggests insulin dysregulation. The oral sugar test (OST) is a dynamic test that assesses the insulin response to a glucose challenge. The combined glucose-insulin test (CGIT) is another option. ACTH testing is recommended to rule out PPID, as the two conditions can coexist.

BMC Veterinary Research published a study on lower plasma trans-4-hydroxyproline and methionine sulfoxide levels associated with insulin dysregulation in horses [15]. These biomarkers may provide additional insights into the metabolic disturbances in EMS. The Journal of Equine Veterinary Science published a study on morphometric, metabolic, and inflammatory markers across a cohort of client-owned horses and ponies on the insulin dysregulation spectrum [16]. The study identified associations between body condition, neck circumference, and metabolic parameters.

The Journal of Equine Veterinary Science also published a study on the prevalence of insulin dysregulation in non-obese stock-type horses and its relationship with morphometric neck measurements [17]. The study found that insulin dysregulation can occur in non-obese horses, emphasizing the importance of screening all at-risk animals.

Treatment of EMS

The cornerstone of EMS management is dietary modification and exercise. The goal is to reduce body weight, improve insulin sensitivity, and prevent laminitis. Horses with EMS should be fed a low nonstructural carbohydrate (NSC) diet, with hay that has been tested for NSC content. Grazing should be restricted, especially during periods of high grass sugar content. Exercise should be implemented gradually, with careful monitoring for laminitis.

Pharmacological options for EMS include metformin, which improves insulin sensitivity, and levothyroxine, which promotes weight loss. SGLT2 inhibitors, such as canagliflozin, have been used to reduce hyperinsulinemia in refractory cases. These medications should be used under veterinary supervision, with regular monitoring of insulin, glucose, and electrolytes.

Insulin Dysregulation

Insulin dysregulation is a central feature of both PPID and EMS. It refers to an abnormal insulin response to glucose, including both insulin resistance and hyperinsulinemia. Insulin dysregulation is the primary risk factor for endocrinopathic laminitis.

Assessment of Insulin Dysregulation

The assessment of insulin dysregulation begins with a thorough history and physical examination. Risk factors include breed, age, body condition, and previous episodes of laminitis. Resting insulin and glucose concentrations are measured after a 12-hour fast. An elevated resting insulin concentration (>20 mIU/L) indicates insulin dysregulation. However, a normal resting insulin concentration does not rule out the condition.

Dynamic testing is recommended for horses with normal resting insulin but clinical suspicion of insulin dysregulation. The oral sugar test (OST) involves administering corn syrup (0.15 mL/kg) and measuring insulin and glucose at 60 and 90 minutes. An insulin concentration >60 mIU/L at any time point is considered abnormal. The combined glucose-insulin test (CGIT) is an alternative that involves intravenous administration of glucose and insulin.

Management of Insulin Dysregulation

Management of insulin dysregulation focuses on dietary modification, exercise, and weight management. The diet should be low in NSC, with hay containing less than 10% NSC on a dry matter basis. Soaking hay for 30 to 60 minutes can reduce NSC content. Grazing should be limited to periods when grass sugar content is low, such as early morning or late evening. Exercise improves insulin sensitivity and should be part of the management plan for all horses with insulin dysregulation.

Pharmacological options include metformin (30 mg/kg orally twice daily) and levothyroxine (48 to 96 mg orally once daily). These medications should be used in conjunction with dietary management, not as a substitute. Regular monitoring of insulin, glucose, and body condition is essential.

Diabetes Mellitus in Horses

Diabetes mellitus is rare in horses but can occur secondary to PPID, pancreatic disease, or other conditions. It is characterized by persistent hyperglycemia and glucosuria. Horses with diabetes mellitus may present with polyuria, polydipsia, weight loss, and laminitis.

Diagnosis of Diabetes Mellitus

Diagnosis of diabetes mellitus is based on persistent hyperglycemia (fasting glucose >150 mg/dL) and glucosuria. Fructosamine concentrations reflect average blood glucose over the previous two to three weeks and can help confirm the diagnosis. Insulin concentrations may be low (type 1 diabetes) or high (type 2 diabetes with insulin resistance).

Management of Diabetes Mellitus

Management of diabetes mellitus in horses is challenging and requires a multidisciplinary approach. The underlying cause should be identified and treated. Insulin therapy may be necessary, using intermediate-acting insulin such as NPH or long-acting insulin such as glargine. Dietary management is essential, with a low NSC diet and controlled feeding. Regular monitoring of blood glucose, fructosamine, and clinical signs is required.

Goiter in Horses

Goiter is an enlargement of the thyroid gland, usually due to iodine deficiency or excess. It is most commonly seen in foals born to mares with iodine imbalances. Goiter can also occur in adult horses with thyroid tumors or inflammatory conditions.

Diagnosis of Goiter

Diagnosis of goiter is based on physical examination and palpation of the thyroid gland. The gland is located just below the larynx and is normally not palpable. An enlarged thyroid gland may be visible or palpable. Thyroid function tests, including T4, T3, and TSH, can help determine if the goiter is associated with hypothyroidism or hyperthyroidism. Thyroid ultrasound can assess the size and structure of the gland.

Management of Goiter

Management of goiter depends on the underlying cause. Iodine deficiency is treated with iodine supplementation, while iodine excess requires removal of the iodine source. Thyroid tumors may require surgical removal. Hypothyroidism is treated with levothyroxine supplementation. Hyperthyroidism is rare in horses but may require antithyroid medications or surgery.

Diagnostic Testing Protocols

Accurate diagnosis of equine endocrine disorders requires appropriate testing protocols. The following steps outline the diagnostic approach for common endocrine conditions.

Step 1: History and Physical Examination

A thorough history should include age, breed, body condition, diet, exercise, previous episodes of laminitis, and current medications. Physical examination should include body condition scoring, cresty neck scoring, and assessment of regional adiposity. The presence of hirsutism, delayed shedding, or other clinical signs of PPID should be noted.

Step 2: Baseline Endocrine Testing

Baseline testing includes resting insulin, glucose, and ACTH concentrations. Blood samples should be collected after a 12-hour fast. ACTH samples should be collected in chilled EDTA tubes and processed promptly. Reference ranges vary by laboratory and season.

Step 3: Dynamic Testing

Dynamic testing is indicated when baseline results are equivocal or when clinical suspicion is high despite normal baseline results. The oral sugar test (OST) is the preferred dynamic test for insulin dysregulation. The TRH stimulation test is used for PPID diagnosis. The combined glucose-insulin test (CGIT) is an alternative for insulin dysregulation.

Step 4: Additional Testing

Additional testing may include fructosamine for diabetes mellitus, T4 and T3 for thyroid function, and thyroid ultrasound for goiter. In cases of refractory laminitis, radiographs of the feet are indicated to assess for rotation or sinking of the coffin bone.

Records and Measurements

Accurate records are essential for monitoring horses with endocrine disorders. The following measurements should be recorded at each visit.

Body Condition Score

Body condition score (BCS) is assessed on a 9-point scale, with 1 being emaciated and 9 being obese. A BCS of 5 to 6 is ideal for most horses. Horses with EMS should have a BCS of 5 or less.

Cresty Neck Score

Cresty neck score (CNS) is assessed on a 5-point scale, with 0 being no crest and 5 being a large, drooping crest. A CNS of 3 or higher is associated with insulin dysregulation.

Neck Circumference

Neck circumference is measured at the midpoint of the neck. An increased neck circumference relative to body size is associated with insulin dysregulation.

Body Weight

Body weight should be measured using a scale or weight tape. Weight loss is a goal for overweight horses with EMS.

Insulin and Glucose Concentrations

Insulin and glucose concentrations should be measured at baseline and after dynamic testing. Serial measurements are used to monitor response to treatment.

Common Failure Patterns

Failure to diagnose or manage equine endocrine disorders can lead to serious complications, including laminitis, infections, and death. The following are common failure patterns.

Failure to Recognize Early Signs

Early signs of endocrine disorders, such as mild hirsutism or subtle laminitis, may be overlooked. Regular screening of at-risk horses is essential.

Inadequate Diagnostic Testing

Relying on a single test or failing to perform dynamic testing can lead to missed diagnoses. A comprehensive diagnostic approach is necessary.

Poor Dietary Management

Feeding a high NSC diet to horses with insulin dysregulation can worsen hyperinsulinemia and increase laminitis risk. Hay testing and grazing management are essential.

Inconsistent Exercise

Exercise improves insulin sensitivity, but inconsistent or excessive exercise can increase laminitis risk. A gradual, consistent exercise program is recommended.

Failure to Monitor Treatment

Regular monitoring of clinical signs, body condition, and endocrine parameters is necessary to assess treatment response and adjust management.

Welfare and Safety Context

Equine endocrine disorders have significant welfare implications. Laminitis is a painful and debilitating condition that can lead to euthanasia. Obesity and insulin dysregulation increase the risk of laminitis and other health problems. The World Organisation for Animal Health (WOAH) provides guidelines on animal health and welfare, including the management of metabolic diseases in horses [5].

Veterinarians have a responsibility to diagnose and manage endocrine disorders promptly to prevent suffering. Horse owners should be educated about the signs of endocrine disorders and the importance of regular veterinary care. The AAEP provides resources for horse owners on recognizing and managing endocrine conditions [1].

Professional Escalation Criteria

Veterinarians should escalate care to a specialist in the following situations.

Urgent Escalation

• Acute laminitis with severe pain, rotation, or sinking of the coffin bone
• Severe hyperglycemia (>300 mg/dL) with clinical signs of diabetic ketoacidosis
• Suspected pituitary tumor with neurological signs (ataxia, blindness, seizures)
• Thyroid storm with tachycardia, hyperthermia, and agitation

Routine Escalation

• Refractory PPID or EMS despite appropriate treatment
• Recurrent laminitis despite dietary management and exercise
• Suspected thyroid tumor requiring surgical removal
• Diabetes mellitus requiring insulin therapy

Practical Decision Framework for Managing Equine Endocrine Disorders

Managing equine endocrine disorders requires a structured approach that integrates diagnostic findings, clinical signs, and treatment response into actionable decisions. This section provides a practical decision framework that veterinarians and horse owners can use to guide management of PPID, EMS, insulin dysregulation, diabetes mellitus, and goiter. The framework emphasizes sequential decision points, monitoring intervals, and escalation criteria based on objective measurements and clinical observations.

Tiered Decision Framework Overview

The decision framework uses three tiers based on disease severity and treatment response. Tier 1 involves initial diagnosis and basic management. Tier 2 addresses cases that do not respond adequately to first-line therapy. Tier 3 involves refractory cases requiring specialist referral or advanced interventions. This tiered approach allows for systematic progression through management options while avoiding unnecessary treatments.

Tier 1: Initial Diagnosis and Basic Management

Tier 1 applies to horses with newly diagnosed endocrine disorders or those with mild clinical signs. The goal is to establish a baseline, implement first-line management, and monitor response over a defined period.

Decision Point 1: Confirm Diagnosis

Before initiating treatment, confirm the diagnosis using appropriate endocrine testing. For PPID, measure baseline ACTH concentration. For EMS and insulin dysregulation, measure resting insulin and glucose, and perform an oral sugar test if indicated. For diabetes mellitus, confirm persistent hyperglycemia and glucosuria. For goiter, palpate the thyroid gland and measure T4 and T3 concentrations.

The Merck Veterinary Manual provides diagnostic criteria for equine endocrine disorders, including reference ranges for ACTH, insulin, and glucose [4]. The American Association of Equine Practitioners offers resources on recognizing clinical signs and when to test [1].

Decision Point 2: Implement First-Line Management

First-line management varies by disorder:

• PPID: Initiate pergolide mesylate at 0.002 mg/kg orally once daily. Adjust dose based on ACTH monitoring and clinical response.
• EMS and insulin dysregulation: Implement dietary modification with low nonstructural carbohydrate (NSC) hay, restrict grazing, and begin a gradual exercise program. Body condition score should be reduced to 5 or less on a 9-point scale.
• Diabetes mellitus: Identify and treat the underlying cause. Initiate dietary management with low NSC feed. Consider insulin therapy if hyperglycemia persists.
• Goiter: Correct iodine imbalance. Supplement iodine if deficient, or remove iodine source if excess. Treat hypothyroidism with levothyroxine if indicated.

Decision Point 3: Schedule Initial Monitoring

Schedule follow-up at 4 to 6 weeks after initiating treatment. At this visit, reassess clinical signs, body condition, and endocrine parameters. For PPID, repeat ACTH measurement. For EMS and insulin dysregulation, repeat resting insulin and glucose. For diabetes mellitus, measure fructosamine. For goiter, reassess thyroid size and function.

Decision Point 4: Evaluate Response

Evaluate response based on objective criteria:

• PPID: ACTH concentration should decrease toward the reference range. Clinical signs such as hirsutism and lethargy should improve.
• EMS and insulin dysregulation: Resting insulin should decrease below 20 mIU/L. Body condition score should decrease by at least 0.5 points. Cresty neck score should improve.
• Diabetes mellitus: Fructosamine should decrease toward the reference range. Polyuria and polydipsia should resolve.
• Goiter: Thyroid size should decrease. T4 and T3 concentrations should normalize.

If response is adequate, continue current management and schedule next monitoring at 3 to 6 months. If response is inadequate, proceed to Tier 2.

Tier 2: Advanced Management for Inadequate Response

Tier 2 applies to horses that do not achieve adequate response to first-line therapy after 4 to 6 weeks. The goal is to intensify management and address factors that may be limiting response.

Decision Point 5: Identify Barriers to Response

Common barriers include:

• Inadequate dietary compliance: Verify that hay NSC content is below 10% on a dry matter basis. Confirm that grazing is restricted. Check for access to concentrates or treats.
• Insufficient exercise: Ensure that exercise is performed at least 5 days per week for 20 to 30 minutes. Increase duration or intensity gradually.
• Concurrent disease: Rule out PPID in horses with EMS, as the two conditions can coexist. Check for dental disease, lameness, or other health problems that may affect metabolism.
• Medication noncompliance: Confirm that pergolide or other medications are administered correctly and consistently.

Decision Point 6: Adjust Treatment

Adjust treatment based on the identified barriers:

• PPID: Increase pergolide dose by 0.001 mg/kg increments every 4 to 6 weeks until ACTH is controlled. Maximum dose is typically 0.01 mg/kg orally once daily.
• EMS and insulin dysregulation: Add metformin at 30 mg/kg orally twice daily. Consider levothyroxine at 48 to 96 mg orally once daily for weight loss. In refractory cases, discuss SGLT2 inhibitors with a specialist.
• Diabetes mellitus: Initiate or adjust insulin therapy. Use intermediate-acting insulin such as NPH at 0.1 to 0.2 IU/kg subcutaneously twice daily. Monitor blood glucose closely.
• Goiter: Adjust iodine supplementation or restriction. Increase levothyroxine dose if hypothyroidism persists.

Decision Point 7: Schedule Follow-Up Monitoring

Schedule follow-up at 4 to 6 weeks after treatment adjustment. Repeat relevant endocrine tests and reassess clinical signs.

Decision Point 8: Evaluate Response to Adjusted Treatment

If response is adequate, continue current management and schedule next monitoring at 3 to 6 months. If response remains inadequate, proceed to Tier 3.

Tier 3: Refractory Cases and Specialist Referral

Tier 3 applies to horses that do not respond to Tier 2 management after 8 to 12 weeks. The goal is to pursue advanced diagnostics and specialist consultation.

Decision Point 9: Consider Advanced Diagnostics

Advanced diagnostics may include:

• PPID: Perform TRH stimulation test if not already done. Consider pituitary imaging (CT or MRI) if neurological signs are present.
• EMS and insulin dysregulation: Perform combined glucose-insulin test. Measure fructosamine and triglycerides. Consider liver function tests.
• Diabetes mellitus: Measure fructosamine and consider continuous glucose monitoring. Rule out pancreatic disease with ultrasound.
• Goiter: Perform thyroid ultrasound and fine-needle aspiration if tumor is suspected.

Decision Point 10: Consult a Specialist

Refer to a veterinary internal medicine specialist or equine endocrine specialist. The American College of Veterinary Internal Medicine (ACVIM) provides a directory of board-certified specialists [3]. Specialists can offer advanced diagnostic and treatment options, including:

• SGLT2 inhibitors for refractory hyperinsulinemia
• Continuous glucose monitoring for diabetes mellitus
• Surgical removal of thyroid tumors
• Experimental therapies such as stem cell treatments

Decision Point 11: Consider Euthanasia

In cases of severe, refractory laminitis or uncontrolled metabolic disease, euthanasia may be the most humane option. The Journal of Equine Veterinary Science published a case report of a mare with recurrent endocrinopathic laminitis linked to EMS that ultimately required euthanasia despite aggressive treatment [14]. This case highlights the importance of realistic prognosis discussions with owners.

Record System for Monitoring Endocrine Disorders

A standardized record system is essential for tracking disease progression and treatment response. The following record system includes fields for baseline data, treatment details, monitoring results, and clinical notes.

Baseline Record

Record the following at initial diagnosis:

• Horse identification: Name, age, breed, sex, color, markings
• Presenting complaint: Clinical signs, duration, severity
• Body condition score (BCS): 1 to 9 scale
• Cresty neck score (CNS): 0 to 5 scale
• Neck circumference: Measured at midpoint in centimeters
• Body weight: Measured in kilograms using a scale or weight tape
• Baseline endocrine values: ACTH, insulin, glucose, T4, T3, fructosamine
• Diagnostic test results: Oral sugar test, TRH stimulation test, combined glucose-insulin test
• Radiographic findings: Foot radiographs if laminitis is present

Treatment Record

Record the following for each treatment:

• Medication name, dose, route, frequency
• Date treatment initiated
• Date and reason for dose changes
• Dietary modifications: Hay type, NSC content, grazing restrictions
• Exercise program: Type, duration, frequency
• Other interventions: Hoof care, dental care, parasite control

Monitoring Record

Record the following at each monitoring visit:

• Date of visit
• Clinical signs: Hirsutism, shedding, lethargy, laminitis, polyuria, polydipsia
• BCS, CNS, neck circumference, body weight
• Endocrine values: ACTH, insulin, glucose, T4, T3, fructosamine
• Treatment compliance: Medication administration, diet, exercise
• Adverse effects: Laminitis, diarrhea, colic, behavioral changes
• Next scheduled visit

Clinical Notes

Record free-text notes on:

• Owner concerns and observations
• Changes in management
• Intercurrent illnesses or injuries
• Prognosis discussions
• Referral recommendations

Troubleshooting Method for Common Management Challenges

The following troubleshooting method addresses common challenges encountered when managing equine endocrine disorders.

Challenge 1: Persistent Hyperinsulinemia Despite Diet and Exercise

Possible Causes:

• Inadequate dietary restriction: Hay NSC content may be higher than assumed. Test hay for NSC content. Soak hay for 30 to 60 minutes before feeding.
• Access to pasture: Even limited grazing can cause hyperinsulinemia in sensitive horses. Use a grazing muzzle or dry lot.
• Concurrent PPID: ACTH elevation can worsen insulin dysregulation. Test ACTH and treat PPID if present.
• Medication noncompliance: Verify that metformin or other medications are administered correctly.

Troubleshooting Steps:

1. Test hay NSC content. Target below 10% on a dry matter basis.
2. Implement strict grazing restriction. Use a dry lot or grazing muzzle.
3. Measure ACTH. If elevated, initiate or adjust pergolide therapy.
4. Review medication administration. Ensure metformin is given with feed to reduce gastrointestinal side effects.
5. Consider adding levothyroxine for weight loss if BCS is above 6.

Challenge 2: Poor Response to Pergolide in PPID

Possible Causes:

• Inadequate dose: Start at 0.002 mg/kg and increase gradually. Some horses require up to 0.01 mg/kg.
• Seasonal variation: ACTH levels are higher in autumn. Adjust pergolide dose seasonally.
• Concurrent disease: Dental disease, lameness, or infections can affect clinical response.
• Medication degradation: Pergolide should be stored in a cool, dry place and protected from light.

Troubleshooting Steps:

1. Increase pergolide dose by 0.001 mg/kg increments every 4 to 6 weeks.
2. Repeat ACTH measurement in the same season as the initial test for accurate comparison.
3. Address concurrent health problems. Perform dental examination and hoof care.
4. Verify medication storage and expiration date.

Challenge 3: Recurrent Laminitis in EMS Horses

Possible Causes:

• Dietary indiscretion: Access to grass, hay with high NSC, or treats.
• Exercise inconsistency: Inadequate or excessive exercise can trigger laminitis.
• Concurrent PPID: Untreated PPID can worsen laminitis risk.
• Severe insulin dysregulation: Resting insulin above 50 mIU/L increases laminitis risk.

Troubleshooting Steps:

1. Implement strict dietary control. Use hay with NSC below 10%. Eliminate all concentrates and treats.
2. Establish a consistent exercise program. Start with hand walking and gradually increase duration.
3. Test ACTH and treat PPID if present.
4. Consider pharmacological intervention. Metformin or SGLT2 inhibitors may be indicated.
5. Obtain foot radiographs to assess for rotation or sinking. Provide therapeutic hoof care.

Challenge 4: Weight Loss in Horses with Diabetes Mellitus

Possible Causes:

• Inadequate insulin therapy: Dose may be too low or frequency insufficient.
• Poor dietary management: High NSC diet can worsen hyperglycemia.
• Concurrent disease: Pancreatic disease, dental disease, or infections can cause weight loss.
• Insulin resistance: Some horses require higher insulin doses or different insulin types.

Troubleshooting Steps:

1. Measure blood glucose and fructosamine to assess glycemic control.
2. Adjust insulin dose based on blood glucose monitoring. Increase by 10% to 20% if hyperglycemia persists.
3. Switch to a different insulin type if response is inadequate. Long-acting insulin such as glargine may be more effective.
4. Rule out concurrent disease. Perform dental examination and abdominal ultrasound.
5. Consult a veterinary internal medicine specialist for advanced management.

Common Failure Patterns in Endocrine Disorder Management

Recognizing common failure patterns can help veterinarians and horse owners avoid pitfalls and improve outcomes.

Failure Pattern 1: Delayed Diagnosis

Delayed diagnosis occurs when early signs of endocrine disorders are overlooked. Hirsutism in PPID may be attributed to normal seasonal changes. Mild laminitis in EMS may be dismissed as foot soreness. Regular screening of at-risk horses, including annual ACTH measurement in horses over 15 years and insulin testing in easy-keeper breeds, can prevent delayed diagnosis.

Failure Pattern 2: Incomplete Diagnostic Workup

Relying on a single test or failing to perform dynamic testing can lead to missed diagnoses. A normal resting insulin concentration does not rule out insulin dysregulation. The oral sugar test is more sensitive for detecting postprandial hyperinsulinemia. Similarly, a normal baseline ACTH in spring or summer does not rule out PPID if clinical signs are present. The TRH stimulation test can confirm PPID in equivocal cases.

Failure Pattern 3: Inadequate Dietary Management

Dietary management is the cornerstone of EMS and insulin dysregulation treatment, but it is often implemented incompletely. Hay NSC content should be tested, not assumed. Grazing restriction must be strict, especially during periods of high grass sugar content. Owners may underestimate the impact of small amounts of grass or treats on insulin levels.

Failure Pattern 4: Inconsistent Exercise

Exercise improves insulin sensitivity, but inconsistent or excessive exercise can increase laminitis risk. Horses with EMS should have a consistent exercise program that is gradually increased. Sudden increases in exercise intensity or duration can trigger laminitis in susceptible horses.

Failure Pattern 5: Failure to Monitor Treatment

Regular monitoring is essential for assessing treatment response and adjusting management. ACTH levels should be monitored every 6 to 12 months in horses on pergolide therapy. Insulin and glucose should be monitored every 3 to 6 months in horses with EMS. Body condition score and cresty neck score should be assessed at each visit.

Failure Pattern 6: Ignoring Concurrent Disease

PPID and EMS can coexist, and untreated PPID can worsen insulin dysregulation. Horses with EMS that do not respond to dietary management should be tested for PPID. Similarly, horses with PPID that develop laminitis should be evaluated for insulin dysregulation.

Welfare and Safety Context for Endocrine Disorder Management

Equine endocrine disorders have significant welfare implications. Laminitis is a painful and debilitating condition that can lead to euthanasia. Obesity and insulin dysregulation increase the risk of laminitis and other health problems. The World Organisation for Animal Health (WOAH) provides guidelines on animal health and welfare, including the management of metabolic diseases in horses [5].

Veterinarians have a responsibility to diagnose and manage endocrine disorders promptly to prevent suffering. Horse owners should be educated about the signs of endocrine disorders and the importance of regular veterinary care. The AAEP provides resources for horse owners on recognizing and managing endocrine conditions [1].

Professional Escalation Criteria for Endocrine Disorders

Veterinarians should escalate care to a specialist in the following situations.

Urgent Escalation

• Acute laminitis with severe pain, rotation, or sinking of the coffin bone
• Severe hyperglycemia (>300 mg/dL) with clinical signs of diabetic ketoacidosis
• Suspected pituitary tumor with neurological signs (ataxia, blindness, seizures)
• Thyroid storm with tachycardia, hyperthermia, and agitation

Routine Escalation

• Refractory PPID or EMS despite appropriate treatment for 8 to 12 weeks
• Recurrent laminitis despite dietary management and exercise
• Suspected thyroid tumor requiring surgical removal
• Diabetes mellitus requiring insulin therapy
• Need for advanced diagnostics such as pituitary imaging or continuous glucose monitoring

The American College of Veterinary Internal Medicine (ACVIM) provides a directory of board-certified specialists in equine internal medicine [3]. Consultation with a specialist can provide access to advanced diagnostic and treatment options, including SGLT2 inhibitors, continuous glucose monitoring, and experimental therapies.

Records and Measurements for Endocrine Disorder Monitoring

Accurate records are essential for monitoring horses with endocrine disorders. The following measurements should be recorded at each visit.

Body Condition Score

Body condition score (BCS) is assessed on a 9-point scale, with 1 being emaciated and 9 being obese. A BCS of 5 to 6 is ideal for most horses. Horses with EMS should have a BCS of 5 or less. Record BCS at each monitoring visit and track changes over time.

Cresty Neck Score

Cresty neck score (CNS) is assessed on a 5-point scale, with 0 being no crest and 5 being a large, drooping crest. A CNS of 3 or higher is associated with insulin dysregulation. Record CNS at each monitoring visit.

Neck Circumference

Neck circumference is measured at the midpoint of the neck using a flexible tape measure. An increased neck circumference relative to body size is associated with insulin dysregulation. Record neck circumference in centimeters at each monitoring visit.

Body Weight

Body weight should be measured using a scale or weight tape. Weight loss is a goal for overweight horses with EMS. Record body weight in kilograms at each monitoring visit.

Insulin and Glucose Concentrations

Insulin and glucose concentrations should be measured at baseline and after dynamic testing. Serial measurements are used to monitor response to treatment. Record values in mIU/L for insulin and mg/dL for glucose.

ACTH Concentration

ACTH concentration should be measured in horses with PPID to monitor response to pergolide therapy. Record values in pg/mL. Note the season when the sample was collected, as reference ranges vary.

Fructosamine Concentration

Fructosamine concentration reflects average blood glucose over the previous two to three weeks. It is used to monitor glycemic control in horses with diabetes mellitus. Record values in umol/L.

Related Farming Guides

• Equine Laminitis: Prevention and Management
• Equine Nutrition for Metabolic Health
• Hoof Care for Horses with Endocrine Disorders
• Exercise Programs for Metabolic Horses
• Senior Horse Care and Management

Frequently Asked Questions

What is the difference between PPID and EMS?

PPID is a neurodegenerative disorder of the pituitary gland that causes excessive ACTH production. EMS is a metabolic syndrome characterized by insulin dysregulation, obesity, and laminitis risk. PPID is more common in older horses, while EMS is more common in younger horses and ponies. Both conditions can cause laminitis and may coexist.

How is PPID diagnosed in horses?

PPID is diagnosed based on clinical signs and endocrine testing. The baseline ACTH measurement is the most common test. A single elevated ACTH concentration supports the diagnosis, but seasonal variation must be considered. The TRH stimulation test can confirm PPID in horses with equivocal results. The dexamethasone suppression test is an alternative but carries a risk of inducing laminitis.

What is the treatment for equine metabolic syndrome?

The cornerstone of EMS treatment is dietary modification and exercise. Horses should be fed a low NSC diet, with hay tested for NSC content. Grazing should be restricted. Exercise should be implemented gradually. Pharmacological options include metformin and levothyroxine. SGLT2 inhibitors may be used in refractory cases.

Can horses with PPID be managed without medication?

Management of PPID without medication is possible in mild cases, but most horses require pergolide mesylate to control ACTH levels and prevent complications. Dietary management, hoof care, and regular veterinary monitoring are essential components of care.

What is the prognosis for horses with laminitis secondary to endocrine disease?

The prognosis for horses with endocrinopathic laminitis depends on the severity of the laminitis and the underlying endocrine disorder. Early diagnosis and aggressive management improve the prognosis. Horses with severe laminitis, rotation, or sinking of the coffin bone have a guarded prognosis.

How often should endocrine testing be repeated in horses with PPID or EMS?

Endocrine testing should be repeated every 6 to 12 months in horses with PPID or EMS, or more frequently if clinical signs change. ACTH levels should be monitored in horses on pergolide therapy. Insulin and glucose should be monitored in horses with EMS.

What dietary changes are recommended for horses with insulin dysregulation?

Horses with insulin dysregulation should be fed a low NSC diet, with hay containing less than 10% NSC on a dry matter basis. Soaking hay for 30 to 60 minutes can reduce NSC content. Grazing should be limited to periods when grass sugar content is low. Concentrates should be avoided or fed in small amounts.

Can goiter in horses be prevented?

Goiter in horses can be prevented by ensuring adequate but not excessive iodine intake. Mares should be fed a balanced diet during pregnancy and lactation. Iodine supplements should be used with caution, as excess iodine can cause goiter.

Related Veterinary Guides

• Diagnostic Medical Sonography Programs
• Swine Respiratory Disease Observation And Diagnostics
• Broiler Respiratory Health Observation And Testing
• Camel Reproduction Management Estrus Detection Ai Calving
• Working Equid Dental Care Routine Problem Management

References and Further Reading

• aaep.org
• www.merckvetmanual.com
• www.acvim.org
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Equine Cushing's disease.. The British veterinary journal, 1993.
• Equine Cushing's disease.. The Veterinary clinics of North America. Equine practice, 2002.
• Pituitary pars intermedia dysfunction: equine Cushing's disease.. The Veterinary clinics of North America. Equine practice, 2002.
• Cushing's Disease in the Animal Kingdom: Translational Insights for Human Medicine.. International journal of molecular sciences, 2025.
• [Equine Cushing's disease, an update].. Tijdschrift voor diergeneeskunde, 2013.
• Cushing's disease: a new approach to therapy in equine and canine patients.. The British homoeopathic journal, 2001.
• In Vitro Generated Equine Hepatic-Like Progenitor Cells as a Novel Potent Cell Pool for Equine Metabolic Syndrome (EMS) Treatment. Stem Cell Reviews and Reports, 2023.
• Orientin Reverses Premature Senescence in Equine Adipose Stromal Cells Affected by Equine Metabolic Syndrome Through Oxidative Stress Modulation. International Journal of Molecular Sciences, 2025.
• Integrating clinical and rna-seq findings in a mare with recurrent endocrinopathic laminitis linked to equine metabolic syndrome.. Journal of Equine Veterinary Science, 2026.
• Lower plasma trans-4-hydroxyproline and methionine sulfoxide levels are associated with insulin dysregulation in horses. BMC Veterinary Research, 2018.
• Morphometric, metabolic, and inflammatory markers across a cohort of client-owned horses and ponies on the insulin dysregulation spectrum. Journal of Equine Veterinary Science, 2021.
• Prevalence of insulin dysregulation in the non-obese stock-type horse and relationship with morphometric neck measurements. Journal of Equine Veterinary Science, 2024.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.