Question

I have a nine-month-old Quarter Horse filly bred specifically for halter competition. She weighs about 640 lb (290 kg). She gets 10 hours of turnout each day, and when she’s not out, she has a 12’ x 12’ stall with a 12’ x 36’ run off the back. She’s fed alfalfa (lucerne) and grass hay in the stall and free-choice grass hay in the turnout. She is also fed 4 lb (1.8 kg) of a low-starch feed and 1 lb (0.45 kg) of a balancer pellet. The filly has had some growth issues, including knuckling over in her front and rear ankles. She was diagnosed with PSSM as well. How can I make sure this filly is being fed properly?

Answer

I think that you may need to address the polysaccharide storage myopathy (PSSM)primarily. Fortunately, the feeding recommendations for PSSM would also be suitable for a yearling with physitis, the developmental orthopedic disease this filly may have.

Horses with PSSM rarely develop insulin resistance because the genetic defect allows for plenty of glucose to enter the cell, which is just the opposite of the action of insulin resistance. For this reason, I would not shy away from fat as an energy source for this horse. In fact, a very low-starch, high-fat diet is what I would recommend for this youngster.

Because you are seeing some effects on the muscle tissues from the PSSM, you may want to reduce the starch level where you can. Even though the product you’re currently feeding is labeled “low starch,” it may still have too much starch for this horse’s condition.

You have some options, such as staying with the balancer pellet and hay with some type of additional fat source (e.g., oil, rice bran) or switching to the feed that was formulated and tested in horses with PSSM, like Re-Leve (not available in Australia or New Zealand).

Vitamin E may be a good idea because of its antioxidant effect on muscle tissue. You may consider supplementing an additional 1,000 IU over what is provided in the feed. Natural-source vitamin E has been found to be more effective than synthetic sources. For more information on the benefit of natural-source vitamin E and for a highly bioavailable source, read more about Nano-E.

One note about alfalfa: it would be better if the horse does not get over 50% of the hay as alfalfa because it tends to be higher in sugar and starch than grass hay.

Consult with your veterinarian about possible conditions that may affect growth and to rule out neurologic diseases that may also cause knuckling.