My Mare (13 yo shire/tb cross, novice level eventer) was diagnosed with EPSM via muscle biopsy in May 2011.
We changed her diet to high fat and increased days of exercise. She is turned out and never locked in a stall. She has improved dramatically and her flat and fence work as been fantastic. She can balance and use her hind end.
Now the issue:
1 week ago she took a couple strange steps (felt like her hip was dropping) tracking left with her left hind at the walk. Sound at the trot.
Sound the rest of the week (Thurs, Fri, Sat-Off, Sun).
Monday she presented with hind end stiffness at the walk, not really stepping under herself with either leg. Once she trotted she was 3 out of 5 lame, dropping her left hip. Every 3rd or 4th step she would drop both hips.
Tuesday, same. After walking for 30 min she seemed to loosen up and have her usual big stride at the walk.
Her hindquarters are not as "hard" as they were when the EPSM was discovered but they do seem tight.
She had a high supensory lesion three years ago, ultrasound showed healed and has been sound since.
No other previous soundness issues.
Does this sound like an EPSM episode?
There haven't been any changes to her diet... The only possibility is the grass? We are in Massachusetts and it has been very warm. I believe the ground needs to be 50 degrees for the grass to grow. Maybe new grass, sugar infux, muscle pain?
In recent reading I discovered I don't think she is getting enough Magnesium. Could this cause general hind end lameness?
Is there anything else related to the EPSM that could cause this?
She has hock rubs but that can mean hock and/or back pain/stiffness causing trouble getting up... She has outstanding hock action so I don't think its her hocks...
It is possibly an EPSM issue... My EPSM gelding will suddenly feel like I have a flat tire behind. Or it could be something else. I might try bloodwork if your horse has previously tied up. My mare with EPSM would go horribly lame in the left front when she would tie up due to the muscle in her shoulder being the first to go. FWIW