Q: I have a 20-year-old former easy keeper that has just been diagnosed with pituitary pars intermedia dysfunction (PPID, once called equine Cushing’s disease). My vet advised I switch him to a low-nonstructural-carbohydrate (NSC) feed to help manage the condition, but my horse has started going off his grain and is beginning to lose weight. How do I balance his need for a low-NSC diet while keeping him eating and at a healthy body condition score (BCS)?

A: This is an increasingly common scenario faced by owners of horses that have historically been diagnosed with equine metabolic syndrome (EMS), a condition in which easy keepers often become less responsive to insulin, that then go on to age into PPID. Your vet has given you some good advice about minimizing the NSC content of your horse’s diet. That’s a foundational part of managing equine insulin dysregulation (ID), meaning the horse produces or responds to insulin abnormally. Insulin dysregulation is certainly associated with an easy keeper phenotype (physical traits) but can also be associated with PPID.  

Because older horses (with or without PPID) might experience loss of body condition and muscle wasting and could benefit from supplemental calories, concurrent ID might make some commercially available calorie-dense diets less safe for horses who need to gain weight (and potentially risk causing or exacerbating laminitis).  

Generally, you should avoid high-NSC diets (over 20% NSC on a dry matter basis) for horses with ID, especially when feeding them in quantities meant to encourage weight gain. Some additional testing for ID (such as an oral sugar test and insulin tolerance test) might be helpful to determine the degree of your horse’s ID.  

Safer calorie sources for horses with ID that need to gain weight include fat and fiber, so consider one or more of the following strategies to encourage a normal body condition in a horse on the thin side: 

1. Ensure PPID is well-managed with appropriate medications prescribed by your veterinarian. 
2. Gradually increase the amount of fermentable fiber in your horse’s diet. If his dentition is still reasonably normal, give him ad libitum access to low-NSC grass hay (and potentially judicious access to pasture if the horse isn’t severely ID). Consider gradually adding legume forage (alfalfa and clover), cubes, or pellets to the diet as well. Alfalfa often gets a bit of a bad rap for horses with metabolic problems, but it can have a lower NSC content than many grass hays. Horses often find it highly palatable, so it might help with your horse’s feed refusal issues. You can also consider gradually adding meals of nonmolassed beet pulp. If he’s not able to chew properly due to the condition of his teeth, adding meals of soaked and mashed alfalfa cubes or pellets or a forage-based complete pelleted diet might be helpful. 
3. Add supplemental fat to the diet, along with a little extra vitamin E. Adult horses can tolerate a surprising amount of fat (up to 20% or more on a dry matter basis), which you can use to encourage weight gain in individuals with ID. Gradually add a fat supplement, such as corn oil, vegetable oil, flaxseed oil, stabilized ground flaxseed, or a commercially available combination product, to increase the caloric density of your horse’s diet. Some fat supplements, such as rice bran, can have a relatively high NSC content as well (20-30%), so carefully consider if this is appropriate before adding it to your horse’s diet. 

As always, fostering a good working relationship with your primary care Veterinarian helps ensure you receive accurate, practical guidance for managing your metabolic horse’s diet and supporting his health over the long term.