Q: I have a senior horse that has pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease) and recently was diagnosed with equine protozoal myeloencephalitis (EPM). For the past few months he’s struggled to maintain a healthy weight and remains very thin despite my adding more calories to his diet. I’m following my veterinarian’s treatment plan for both conditions, but what can I do to support my horse nutritionally in the meantime?

A: Managing nutrition for senior horses can be challenging, especially when multiple health issues are at play, such as PPID and EPM. It’s great your veterinarian is closely involved and treating both conditions because that’s a critical first step.

Understanding PPID and EPM

Pituitary pars intermedia dysfunction is a hormonal disorder, typically of older horses, that causes muscle loss, immune challenges, and sensitivity to sugar and starch. Equine protozoal myeloencephalitis is a neurologic disease caused by protozoal parasites that damage the central nervous system, often leading to weakness, weight loss, and muscle wasting.

Managing either condition can be difficult on its own, but when they occur together, horses face both the metabolic restrictions of PPID and the added nutrient and calorie demands of EPM. That combination makes thoughtful nutrition especially important in supporting weight gain and overall health.

When feeding an older horse that needs to gain weight, start by considering how well he chews and digests forage. Senior horses often struggle with dental wear or reduced digestive efficiency, which can limit how much nutrition they absorb from their feed. In horses with PPID and EPM, these age-related changes add another layer of challenge, making every calorie count.

Choose a High-Quality Forage for Your Horse

Feeding low-quality forage, can make weight gain difficult, especially considering hay makes up the bulk of most equine diets.

So, if your horse can still chew long-stem forage comfortably, start by offering higher-quality hay; choose a less mature grass/legume mix instead of an overly mature grass hay. Have your hay tested before feeding to confirm the nonstructural carbohydrate (NSC) content measures at or below 10% for your PPID horse. Some hay suppliers provide nutritional analyses or list typical NSC levels for their hay types so you can check starch content before you buy.

If you’re unable to provide higher-quality hay, or if dental issues make chewing hay a challenge, consider hay cubes, chopped hay, or pellets. Many high-quality commercial fiber-based feeds can also replace or supplement the forage portion of your horse’s diet when needed.

Choosing the Right Concentrate Feed for Your Horse

After you’ve addressed forage quality, select a concentrate feed that meets your horse’s specific needs. A low-NSC, high-fat senior feed often works well for PPID horses that have trouble with weight gain. Manufacturers have formulated these feeds to be easily digestible, and their higher fat content boosts calorie density without adding excess starch and sugar. Be sure to follow the feeding directions on the label, because feeding below the recommended rate can lead to nutritional deficiencies.

Adding Supplements to Your Horse’s Diet

With high-quality forage and an appropriate senior feed in place, you can use supplements to fine-tune calorie intake and nutritional support for your PPID horse. Adding an omega-3–rich oil can increase the meal’s caloric density while potentially providing anti-inflammatory benefits for a senior horse with health conditions.

Horses with EPM often benefit from additional vitamin E, which also helps address inflammation. Vitamin E is an antioxidant that combats free radicals—tiny particles that can cause extensive damage at the cellular level. Veterinarians see a lot of inflammation in and damage to nerves and surrounding structures in EPM horses, making antioxidants crucial.

Researchers and nutritionists typically recommend 5,000 to 10,000 IU per day orally—but always discuss this with your veterinarian. Many veterinarians recommend testing to get a baseline vitamin E level on your horse before beginning vitamin E supplementation.

Take-Home Message

In many cases senior horses with PPID and EPM that struggle to gain weight simply aren’t consuming enough digestible fiber, often because they can no longer chew hay effectively and/or they are eating lower-quality forage. Key first steps include testing your hay and making sure you’re feeding the correct amount of concentrate. From there, adding an omega-3 oil and extra vitamin E (if needed) can provide additional support. Because this is a complex case involving multiple conditions, it’s wise to work closely with a qualified equine nutritionist and your veterinarian. They can evaluate your horse’s full health and management history and help you develop a balanced, individualized feeding plan to support both weight gain and long-term wellness.