The high fat diet is an excellent prevention diet. EPSM is a metabolic disorder and studies have shown it's because the horses can't handle the starches and sugars in grain and other sweet feeds.
Dr. Beth says, " Fortunately for draft horses and their owners, feeding the horses a diet that is low in soluble carbohydrates and high in fat appears to effectively control signs of EPSM. A diet change prior to the onset of any serious problems is much preferred and is part of good draft horse management".
So, while it's great your horse hasn't exhibited any issues, overall it is just good practice to go with prevention and feed a high fat diet. Plus there are tons of other great reasons that it's beneficial to the horse (or even light horses).
From her book:
- Decreases body heat production with exercise
- Decreases risk of colic, founder and gastric ulcers
- Provides a ready source of energy that does not have to be chewed
- Provides high energy feed in a low volume
- Improves respiratory function in horses with chronic respiratory disease
- Enhances oxidative metabolism
- Controls or prevents EPSM
- Avoids OCD (a joint disease)
- Improves haircoat and skin
- Possibly protects from post-anesthetic muscle problems
So there are a lot of good reasons for draft owners to use it other than EPSM prevention. It doesn't mean that it will keep your horse entirely from getting it, but it's better to try then to have the horse end up with it.