Part II: Misdiagnosed & Misunderstood – PSSM in Horses

One challenge with a lot of these horses, whether they are Type I, Type II, PSSM or EPSM, is that they may be easy keepers and overweight at the time of the diagnosis. And the "cure" adding calories in the form of fat may help alleviate the disease but potentially create other complications from being overweight.

Story originally posted by: by Eleanor D. Van

Read Part I of this article here.

Managing Diet And Symptoms

When I started the high fat diet this Spring, my own horse was actually underweight, (after a difficult winter) for one of the few times in her life, so this was not a concern to me. However, it is something that will need to be watched closely. Just three months into the daily ration of oil and rice bran, I am working hard at keeping her at a good weight without muzzling her from the grazing. For now, I am trying to diligently ride and exercise her more. I also know that she feels better now, so she moves more during the day when she is out in pasture with a group of lively mares on several sloping acres. To relegate her to a dry lot turnout with no horse buddies would decrease her exercise and depress her, so caloric intake is a balancing act just as is the sugar/fat regulation of her diet.

Each owner needs to tailor his or her horse’s diet carefully with help from their own veterinarian (who is hopefully well-versed in PSSM/EPSM and knowledgeable of the individual horse’s symptoms). The owner and/or their vet need to formulate a diet that both meets energy requirements and reduces muscle pain and the progression of the disease. If you do not have a veterinarian who is familiar enough with this disease to help you with this, there are resources on the web such as that of Dr. Valberg and also the Rural Heritage site and forum for EPSM from Dr. Valentine. Dr. Valentine recommends one pound of fat (about two cups of oil) per 1000 lbs of horse, and indeed, when I reached this level with my own horse she had the greatest improvement.

Remember, though, it is not just high fat that is a requirement but also low sugar. Dr. Valberg warns that “because insulin stimulates the already overactive enzyme glycogen synthase in the muscle of type 1 PSSM horses, selecting hay with 12% or less NSC is advisable.” (If you are a boarder and at the mercy of your barn for hay, this won’t be easy but it is not insurmountable just pay strict attention to the fat and exercise). You can get advice and most of the information that you need on grass, hay, and sugar from Kathryn Watts’ site called www.Safer

The diet management takes some thought and planning, but fortunately it won’t take rocket science to get your horse well. Dr. Valentine summarizes it by stating “the best diet for your EPSM horse is one you are happy buying that your horse is happy eating, and that keeps your horse’s muscles healthy.”

Get Moving

Exercise and movement play a critical role in reversing the effects of this disease. Exercise encourages removal of glycogen from the cells and trains them for utilization of fat. The low-starch, high fat diet basically restricts glucose uptake into muscle cells and at the same time provides more free fatty acids for use in muscle fibers during aerobic exercise, according to Dr. Valberg. This, coupled with exercise that “trains” the cells to use fat instead of glucose, ultimately results in the decrease of symptoms and a more pain-free, energetic horse and one who is freer to use his or her muscles to their full extent.

Willing But Unable

Without the aforementioned diet and exercise plan, PSSM/EPSM horses with chronically tight, sore muscles may be called lazy, stupid, disrespectful, resistant, and worse by owners and trainers attributing certain behaviors and resistance strictly to attitude and work ethic. These horses also may be put on a myriad of supplements that never improve their situations, further frustrating their owners. Then they may be sold and change hands frequently, or deemed fit solely for a job of reproduction with their excellent bloodlines, potentially passing on the disease to future generations.

Dr. Valentine believes that this disease was unwittingly selected for and bred into horses like the gentle giant draft horses and the “golden retriever” of the horse world, Quarter Horses. It is especially heartbreaking when you consider that these horses are normally incredibly willing, intelligent creatures who would do whatever was asked of themif only their bodies would cooperate.

Make the Right Thing Easy

When the diet and exercise recommendations are followed, most afflicted horses will show improvement. According to Dr. Valberg, however, “there is a wide range in the severity of clinical signs shown by horses with PSSM; those horses with severe or recurrent clinical signs will require more stringent adherence to diet and exercise recommendations in order to regain muscle function.” As with any disease, tailoring the treatment plan to the individual patient can have an enormous impact on the health and well-being of that patient.

In the horse world, we often hear the phrase “make the right thing easy and the wrong thing difficult”. For the PSSM/EPSM horse, this may have more to do with the feed room than the round pen or arena. There is no stick, halter, special saddle or gadget that will ever ease their discomfort, or make them “behave”, without addressing the diet first. It is important to understand that almost everything involving movement for these horses can be difficult, not easy, no matter how smart, well-bred, or willing to please they may be. We owe it to them to get them well so that doing the right thing is truly easy for them.


Eleanor D. Van Natta is a publicist and writer who lives outside of Portland, OR with her family. She has a degree in Zoology from the University of CA, Davis and is a lifelong lover of animals, especially of the equine kind. You can read more about her own horse’s struggle with PSSM on her website