A comprehensive guide to equine metabolic diseases and how to support them naturally
BY STEPHANIE CARTER
How well do you understand your horse’s metabolic diagnosis? There’s many types of equine metabolic dysfunctions, and it’s important to know how to support them using both conventional treatment and through a functional nutrition approach.
First, let’s define functional nutrition. Functional nutrition is a modality used by functional medicine which focuses on identifying and addressing the root cause of disease. Each symptom or diagnosis may be one of many contributing to an individual horse’s illness. Functional nutrition is the use of food to improve, prevent, or reverse health conditions.
As a Functional Nutritional Therapy Practitioner (FNTP), my approach is grounded in bio-individuality. There isn’t a one-size-fits-all diet. Nutritional therapy is holistic in nature, and we aim to support the entire body as a network of systems rather than addressing specific symptoms.
Understanding Equine Metabolic Conditions
Technically, there are only two categories of equine metabolic disorders, however, for ease of understanding, I like to break them into three separate classifications:
- Equine Metabolic Syndrome (EMS): Considered a “young horse” disease (5 to 15 years of age), EMS has a physical presentation which includes obesity or regional adiposity (fat pads) with a tendency to develop laminitis and possible genetic predisposition. Typically, it is also considered a precursor to Cushing’s Disease. It’s diagnosed by bloodwork with results showing elevated insulin and sometimes adrenocorticotropic hormone (ACTH).
- Hyperinsulinemia (Insulin Resistance [IR], Insulin Dysregulation): Symptoms include abnormal weight gain or loss, increased or excessive water consumption, loss of stamina or muscle tone/definition, frequent and/or persistent hoof bruising (often red or reddish-purple spots on the soles), a tendency to develop laminitis, and excessive hunger. It’s also considered a precursor to Cushing’s and is diagnosed by bloodwork showing increased insulin value.
- Pituitary Pars Intermedia Dysfunction (PPID or Cushing’s): Commonly called Cushing’s disease, PPID is often considered an “old horse” disease (15 years and up). Symptoms include hypertrichosis (long hair coat); sweating issues, either too much (hyperhidrosis) or too little (anhidrosis); muscle atrophy and poor topline; pendulous abdomen (potbellied), and decreased intestinal wall integrity, recurrent infections (including hoof abscesses) due to suppressed immunity, tendency toward increased parasite load, lethargy and/or depression, polydipsia and polyuria (increased drinking and urination). It’s diagnosed by bloodwork indicating an elevated ACTH.
The Role of Blood Sugar Regulation, Insulin, and the Liver
With hyperinsulinemia, it is important to have a basic understanding of blood sugar regulation (BSR). Now, before you get overwhelmed by the intricacies of the associated graphic, know that the point is that the liver plays a huge role in not only filtration but also in BSR as well.
Homeostasis in this example is “regulated” or “stable” blood sugar. As your horse consumes food and digests it, this stimulates blood glucose levels to rise, which triggers the pancreas to release insulin into the blood. Insulin then signals the cells to absorb glucose to use for energy or the liver to store it as glycogen for future needs. As a result, blood glucose levels decrease, and homeostasis is achieved.
The reverse happens when horses go for extended periods of time without eating or consume diets that are high in carbohydrates/sugars, like conventional grain-based feeds. It is also important to note: glucose is not the issue in horses with EMS or IR, but rather elevated insulin.
Beyond the liver’s role in blood sugar regulation, it is also the body’s primary filtration system, converting toxins into waste products, cleansing the blood, and metabolizing nutrients and medications to be more bioavailable and/or non-toxic. Toxins are anything the body does not recognize as a nutrient or something it can use to fuel the cells.
When the liver encounters toxins and it cannot eliminate them from the body via natural detox pathways (kidney, lymph, manure, urine, sweat), it stores the toxins in its tissues. As the liver reaches ‘maximum storage capacity,’ this triggers the body to create excess adipose tissue (fat pads) to store those excess toxins in and protect the body. This is why we frequently hear fat pads being referred to as ‘chemical factories’ due to the inflammation that is caused by these stored toxins.
If your primary-care veterinarian draws blood for a metabolic panel that includes leptin, and the leptin value is high, this is an indication that the liver is burdened and needs support.
The Critical Role of Stress in Metabolic Conditions
During the discussion with your vet about your horse’s metabolic diagnosis, how much time was spent talking about stress and its impact on your horse’s health? Just as with the BSR graphic, try not to focus on the complexities of stress, but rather that stress causes an elevation in cortisol (the stress hormone), and all the negative impacts it has on the body’s physiology.
Stressors can be any of the following, but certainly are not limited to: changes in herd dynamics or barn, acute or chronic pain, tick-borne diseases, systemic pH imbalance, heavy metal burden, unhealthy microbiome, vaccination, owner’s emotional state or energy (Horses have an amazing ability to mirror those around them.), traveling, showing, training, seeing vet or farrier, changes in feed, environmental factors, trauma/abuse, lack of forage, lack of turnout, environmental factors/contaminants
When a horse is stressed, acutely or chronically, it causes an elevation in cortisol, which causes a myriad of issues within the body. If low-grade stress is ignored, it builds, becoming more significant. As a result, the adrenals become fatigued, and their ability to produce adequate amounts of cortisol is diminished.
Understanding Cushing’s Disease (PPID)
Before we can fully understand Cushing’s, we need to understand the basics of the endocrine system, particularly the HPA Axis (Hypothalamus-Pituitary-Adrenal Axis). The HPA Axis is a system of glands that when functioning optimally, are in a constant feedback loop of hormonal communication with each other. The glands that make up the HPA Axis are as follows:
Hypothalamus – Manager of Hormones – Secretes corticotropin releasing hormone (CRH)
Pituitary – The Master Gland – Made up of three hormone producing lobes: pars distalis (responsible for prolactin), pars nervosa (vasopressin), pars intermedia (secretes ACTH)
Adrenals – Spark Plugs for Life – Secrete cortisol
Once a horse is in an extended or advanced stage of chronic inflammation, nutrient deficiency, and the systemic stress of both, as well as external stressors are left unaddressed, it is likely the horse will have progressed through the stages of endocrine disruption and is now suffering from Cushing’s.
When the HPA Axis is functioning optimally, stress, regardless of good or bad, triggers the hypothalamus to release the hormone CRH, which signals the pituitary to release ACTH (the hormone used to diagnose Cushing’s). ACTH tells the adrenals to release cortisol, which cycles back to the hypothalamus telling neurons (cells that send and receive messages from the brain to the body) to release dopamine which inhibits the production and release of ACTH from the pituitary.
Rethinking Cushing’s: Is the Pituitary Really the Problem?
Just because a horse has an elevated ACTH on bloodwork, from a functional medicine standpoint, doesn’t necessarily mean the pituitary isn’t functioning well.
Despite the present science that points to the pituitary being dysfunctional when there is an elevated ACTH, if we understand how a healthy HPA Axis functions, we can deduce that if ACTH is elevated, then there is likely a need for dopamine. If there is a need for dopamine, there is likely not enough cortisol being released by the adrenals, which also means that the pituitary may produce excess ACTH in an attempt to stimulate the adrenals to pick up the slack. (Remember the glands communicate in a constant feedback loop of hormones).
Clinically, when I see horses who have already been prescribed Prascend (pergolide), the medicine used by most vets to suppress ACTH, yet their ACTH values continue to increase despite daily administration, I have found the adrenals are so fatigued and unsupported that they cannot keep up with the demand for cortisol output to complete the hormonal process to regulate ACTH secretion.
By reducing systemic inflammation, supporting adrenal function, and targeted amino acid therapy, it is possible to control Cushing’s and/or significantly reduce the needed dose of Prascend.
Conventional Treatment Approaches for PPID (Cushing’s)
Conventional medicine commonly uses what is called a ‘Standing ACTH’ or TRH Stim test. Based on the results of this bloodwork, your veterinarian will determine whether your horse has an uncontrolled ACTH.
If your horse’s ACTH is elevated, your vet will likely recommend the drug Prascend (generic name: pergolide). Prascend is a dopamine agonist drug that activates dopamine receptors and may help suppress ACTH.
Side effects of Prascend include depression, lethargy, and lack of appetite. Many horse owners report their horses not eating well after starting Prascend. Veterinarians should discuss the importance of slowly titrating the dose as well as feeding it after meals to avoid anorexia.
The appropriate titration protocol of Prascend as outlined by the ECIR group is as follows:
“Whether increasing or decreasing dosage or just starting pergolide for the first time, taper at a rate of 0.25 mg every three days. Ordering a supply of 0.25 mg capsules makes tapering easier.”
Please always have a conversation with your veterinarian before changing dosing of any prescribed drugs. It is dangerous to alter or stop the dose of Prascend (pergolide) without veterinary supervision.
Conventional Treatment for EMS and Insulin Resistance
Conventional medicine commonly uses metabolic panels that can be customized to include the values your vet is concerned might be an issue for your horse. For the purpose of an EMS and/or hyperinsulinemia diagnosis, they will likely be focused on insulin and ACTH. Other values they may evaluate include glucose, leptin, and T4.
If your horse has elevated insulin, conventional treatments may include:
- Metformin: A human drug that reduces glucose (remember the issue in horses is insulin)
- Insulin Wise
- Thyro-L (levothyroxine): Used for underactive thyroid, though human medicine advises against its use for weight loss
- Steglatro (ertugliflozin): An expensive human drug (~$350+/month) that was developed to reduce glucose in humans
- Dry lot or stall confinement
- Restricted caloric intake (including forage)
- “Low starch” meals and soaked hay
- For pain management during laminitic events: NSAIDs like Bute, Banamine, Equioxx, and the anticonvulsant Gabapentin
Important note: If T4 levels are low, from a functional perspective this doesn’t necessarily indicate thyroid dysfunction. It’s likely a symptom of broader endocrine system issues. In human medicine, long-term levothyroxine use has been found to cause thyroid failure when used inappropriately or for extended periods.
The Functional Nutrition Approach: Prevention and Reversal
Unlike conventional medicine, which relies on “one-size-fits-all” treatments and usually after disease onset, functional nutrition focuses on preventing and supporting horses with EMS, IR, or PPID through individualized approaches.
Conventional treatment plans often act as band-aids—treating or suppressing symptoms without addressing underlying causes. Disease, regardless of type, is a symptom of deeper problems typically rooted in inflammation and/or deficiency.
The good news is hyperinsulinemia can be reversed and managed through diet alone. In some cases, even PPID (Cushing’s) can be controlled through dietary changes. However, because PPID represents an advanced stage of dysregulation and deficiency, it sometimes still requires medical intervention—though commonly, at least with my nutrition clients, the dose of medication can be minimal so long as dietary changes are also made in conjunction. All changes in medication should be done in consultation with a veterinarian.
Functional Medicine Diagnostics and Screenings for all Metabolic Conditions
Blood tests such as a CBC/Chem, metabolic panel, and tick disease panel are the foundation of our assessment process. In the practice I worked for in Virginia, we found that more often than not, horses who had elevated insulin levels also had either acute or chronic Lyme disease. Once treated, the insulin level often came back within reference range. Hair Tissue Mineral Analysis (HTMA) is another screening tool that provides additional insights into your horse’s physiological function and potential toxicity issues, such as heavy metal burden. Microbiome testing can offer answers about your horse’s digestive health and immune function.
Taking Action: Diet is Everything
For metabolic conditions, diet is truly everything—it can be the difference between life and death. Respecting horses’ natural instincts is fundamental to their health. Many common care practices force horses to compromise physiologically and psychologically, creating stress that leads to problems like hyperinsulinemia, laminitis, ulcers, and many other medical issues.
Free-choice forage feeding, contrary to popular belief, does not increase obesity or laminitis risk. Wild horses do not suffer from laminitis because they feed naturally, though they do experience insulin resistance as a survival mechanism during food scarcity.
When we restrict forage, horses enter survival mode, maintaining body fat through elevated insulin levels. Stress increases cortisol, raising insulin and contributing to obesity—a connection well-documented in humans and applicable to horses. The conventional approach of limiting hay to 1.5% or even 1% of body weight causes weight loss primarily through muscle loss, creating stressed horses with slow metabolisms that can never return to normal grazing.
Our feeding schedules have disconnected horses from their instinctive ability to eat slowly and stop when satisfied. Instead, they eat ravenously because they do not know when food will be available next and develop abnormal behaviors around feeding time.
Horses’ digestion fundamentally requires continuous eating: stomach acid needs neutralizing through chewing-produced saliva, the digestive tract needs exercising through steady forage flow, and the cecum must remain full to function properly.
The solution is to provide continuous access to suitable hay (low in sugar, starch, and calories), distribute it to encourage movement, and incorporate exercise when appropriate. When horses lose weight this way, their metabolism remains healthy, often allowing eventual return to normal pasture grazing.
The key is establishing trust by ensuring forage is always available. Even a 10-minute gap can trigger overeating and hormonal responses that risk laminitis. Within weeks, most horses begin eating only what they need, regaining their natural instincts, and displaying improved behavior.
This approach has proven successful for many horses, resolving issues from obesity to chronic laminitis, Cushing’s disease, and metabolic syndrome. While this may seem revolutionary, it’s actually returning to horses’ natural feeding patterns, a necessary shift similar to the way we’ve moved away from high-starch diets.
Every horse owner can implement some basic concepts on their own. This includes feeding to reduce inflammation (the root cause) and supporting species appropriate blood sugar regulation. Avoid feeding conventional soy, wheat and wheat by-products (such as middlings), corn, molasses, and canola. They should also include high-quality vitamin/mineral supplements. The most common equine deficiencies are zinc, phosphorus, magnesium, and B Complex.
Our goal is to feed a species appropriate, nutrient-dense, real foods diet. For horses that means forage first, always.
Every horse is a bio-individual. What works for one does not always work for another. When selecting hay, choose varieties with Non-Structural Carbohydrates (NSC) of 12% or lower, ideally 10% or lower. I prefer grass and grass mixes and recommend avoiding alfalfa. This hay should be available at all times, never, ever running out. Forage pellets made from timothy, orchard, or teff can supplement the diet when needed for additional macronutrients. Remember that restriction will compound insulin dysregulation and stress, so continuous access is essential. They will self-regulate with time.
Healthy fats are another critical component. Fat does not equal obesity. Healthy fats are crucial to the body’s ability to inflame and anti-inflame appropriately. They promote energy transfer and storage while maintaining healthy hormone production.
Not all forms of vitamins and minerals are created equally. A high-quality vitamin and mineral supplement is harder to source than one might think. Avoid those containing zinc sulfate which acts as a pesticide, is produced artificially, is highly inflammatory, and bio-unavailable. Increase magnesium, though which form and how much depends on the bio-individuality of each horse. Increase phosphorus, which is in charge of ATP production (energy at a cellular level), and boost B complex intake, at least initially. Targeted amino acid therapy should be personalized—which amino acids will depend on how your horse presents and what disease(s) have been diagnosed.
About the Author
Stephanie Carter of Indigo Ancestral Health has over twenty years of clinical experience as a veterinary technician, previously serving as case manager and functional nutritionist at True North Equine Functional Medicine in Marshall, Virginia. Carter now offers her expertise remotely to horses and their owners throughout North America and collaborates with veterinarians of all specialties. She has successfully supported equine clients suffering from gastric ulcers, Cushing’s, Lyme disease, Insulin Resistance, laminitis, EPM, squamous cell carcinoma, allergies, and various other ailments. Find case studies at StephanieCarterNTP.com
