What are some reasons a horses top line will decline? This horse is 14, not quite a "senior". Is on a good feed program and is turned out 24/7. We power packed him, and plan to get teeth checked. He hasn't been being ridden as much so maybe lack of physical fitness? Any other suggestions?

Not saying this is it by any means, but EPM will definitely do it.

I was afraid of that. He hasn't shown any other signs but maybe I'll run a treatment through him to rule it out. 

I took one of my mares off grass pasture so she could wear her cribbing muzzle full time without issue. I've been throwing her enough hay (top quality alfalfa) to be basically free choice and she still dropped some topline. I've upped her renew gold and am starting to do more dressage type workouts with her to try to help. She doesn't look bad in the slightest, I just like a flat back on my guys. 

I know I sound like a broken record, but, I always go to the teeth first if nothing else has changed but the horse has. A sore mouthed horse may eat just as much as it always did, but only chew it enough to swallow it. When that happens, the roughage arrives in the hind gut without being broken up enough for proper digestion. The result is that much of the nutrition passes on through to end up on the ground behind the horse. If a horse is eating plenty and not holding normal condition, we almost always find a problem in the mouth.

Mine just tested positive for both strains of EPM and not a single symptom, passed a physical neuro eval too. Still treating anyway. But a decrease in workload can do it or if they're just a bit sore somewhere else and not using themselves 100% correctly, 

Thank you guys. You've given me several things to ponder. Hopefully we can get him back to his old self quickly.