Managing a Young Horse with PSSM

I have a Clydesdale/Friesian cross just turned 2 yrs old filly. She is 16h and weight is good, not wanting her to get any heavier. She came to me 4 weeks ago on a local grain that was a 10% – 12% protein pelleted mix, not sure of the fat, but was on 1/3 cup Omega Horseshine 2x day and about 7 1/2#’s of this grain per day. I switched her to Blue Seal Sentinel Grow and Excel extruded. 14% protein and 10% fat, of about 8#’s per day with the same amount of Omega Horseshine for about 4 weeks. Seeing that this new grain had Omega’s in it, I stopped the Omega Horseshine for about a week and also concerned that I didn’t want her any heavier….and within a week, noticed that she had some erratic stepping with her hind legs at times.

She is also on free choice orchard grass hay. She does use the salt lick alot also. I did do some research on EPSM and this sounded like the movements, so I switched her to Triple Crown Low Starch grain which has a NSC value of 13.5%…no corn, no molasses, no alfalfa. 13% protein and 6% fat. The other Sentinel grain had molasses, which, if she has EPSM, she should not have, that is why I switched to the Low Starch. She was also getting horse treats that contained molasses, which I have stopped. I am giving her 6#’s of Low starch grain every day and 1/3 cup of Omega Horseshine, 2x day, to bring her fat content up a bit, as this is important for EPSM. She was going out on pasture for a few hours daily, but only on about a 60 foot by 60 foot grass area, which is kept short by mowing, so she wasn’t getting alot at all. I have stopped this also…..can I continue with this, or keep her off all grass at this point? Am I doing the right thing and should I change anything? Thank you for your help, I appreciate it.:) Carolyn

Dear Carolyn,

Ordinarily I’m fine with owners feeding and managing horses for EPSM (or PSSM, Polysaccharide Storage Myopathy) even if they don’t have definite diagnosis. For most adult horses, reducing simple sugars, adding a bit of fat, and increasing turnout and exercise are beneficial or at least not harmful.

However in your case you’ve got a young horse that still needs higher levels and slightly different ratios of certain nutrients to grow correctly. So for your specific situation, I would ask a veterinarian to examine her for true signs of PSSM, perform specific testing for the disorder if indicated, and, based on the outcome of this testing, develop a diet and exercise protocol that will reduce the signs of PSSM while still meeting her nutritional requirements.

What are the exact differences in diet for an adult horse vs. a just-turned two-year-old like yours? The NRC Nutrient Requirements of Horses has tables in the appendix that list the Daily Nutrient Requirements of Horses with mature weights ranging from 200kg (440lbs) to 900kg (1980lbs). Being part draft, I’m guessing your filly will fit best into the 600kg (1320lb) range when she’s reached her full size. Next, under the heading “Growing Animals” there are several 24 month choices: no exercise, light, moderate, heavy or very heavy. I don’t see in your question any mention of starting training yet so I’m going to look at the line for “no exercise.” In addition to more energy (calories), a two-year-old horse needs more crude protein (including lysine) than the adult horse, almost twice as much calcium, Vitamin D and Vitamin E, plus more phosphorus, iron, manganese, zinc, and Vitamin A. With all these differences—some of them substantial—without a definite diagnosis of PSSM I recommend you focus more on her needs as a growing animal to give her the best start you possibly can.