Because he has tied up, I would assume you are probably dealing with PSSM type 2 or MFM. I would get a muscle biopsy. Keep up the vitamin E and add protein. As much protein as you can. Be careful of too much sugar.
The struggling to maintain the canter is a pretty classic sign of PSSM type 2. As is the tripping.
My PSSM 2 mare is severely exercise intolerant and 20 minutes of light walk/trot exercise will provoke symptoms. Usually she runs out of energy and then starts to trip, struggles to pick up her feet.
Ask him to canter right when you start working him (no warm up). Can he canter normally at this time? Then do walk/trot for 10-15 minutes and ask for the canter again. If the canter deteriorates thatâs a pretty suspicious sign of a muscle disease. Donât do this under saddle. You want to see how he is moving.
Unfortunately the prognosis sounds poor no matter what the issue is. Muscle diseases are not something that the diet alone will cure and itâs something that has to be managed continuously and the horse may continue to have symptoms.
My mare is happy as a pasture pet and is happy to walk around the yard and maybe go for a really short hack down the street and back. Thatâs it. She will always be limited, which is a shame because she had such amazing potential (and as a younger horse she would jump anything you pointed her at). She was never quite right behind. It wasnât lameness- it didnât feel painful but itâs like her muscles just never really worked right. She runs in the pasture and acts like a happy horse, just canât perform any sort of prolonged exercise. A short sprint and sheâs done.
If it turns out to be something else, please let me know. I did not do exhaustive diagnostics because my mare is a pasture pet for the most part and finding out what is wrong isnât going to change her situation.
Could all this be related to the vitamin E deficiency ? I would think itâs possible. I also think sometimes these horses just donât utilize vitamin E the way they should.