Trying to find correct diagnosis
This is very long, but I wanted to provide every clue possible. I am completely baffled by my horse. About 4 weeks ago, he seemingly forgot how to canter. I'd ask him to canter, and instead he'd offer up a big trot in it's place. Lately he has been unwilling to trot for very long either. He'll do it, but it's clear he'd rather be walking. He's stepping a little short with his
hind legs and reacts a little to back pressure from his withers to his hips, but nothing very pronounced. He is not in any way lame, and is not showing any outward signs of pain. No ear pinning, tail swishing, etc. . His walk is very energetic. He'll do whatever lateral move I ask with no problems. It's like he wants to do what I ask, but simply can't. He'll take a few steps of trot or canter and then just quit. No heavy breathing or signs that he's trying to get air.
Basically the only symptom I have to go on is, he's pooped. The only thing I
know for sure is that it's getting worse. I took him out to his favorite field
today. There's a hill he used to run up like a nut. Today he trotted up him
pulling himself up on his forehand and grunting the entire way. It sounded like he was breathing heavy, but as soon as we stopped at the top of the hill, he wasn't breathing heavy. Before this all started, this boy was the energizer bunny. He never thought about stopping. He seems as frustrated as I am that he can't get into gear. He did have several episodes of falling asleep in the cross ties about a month ago. We thought it was sleep deprivation. A paddock change seems to have fixed it. He hasn't fallen asleep in the cross ties since.
This is what I do know:
His bloodwork is normal, he's not anemic
Tested for Lyme, Titer came back very low, he's also not cranky or sensitive to
grooming so it doesn't really fit.
Tested for vitamin E deficiency but it came back fine
He was recently diagnosed with a grade 2 heart murmer, tricuspid valve
regurgitation. Since then I have been monitoring his heart rate. His resting
rate never changes from 36 bpm and his recovery rate is fantastic. He's back to 36 within 2 minutes of trotting. Doesn't really fit with a horse who can't get air.
We did a bute test to see if maybe he tweaked something. Buted him 3 times over 2 days and then rode him to see if he went better when feeling no pain. There was no change.
We did a basic exertion test. We lunged him W/T/C and then the vet listened to his heart and lungs, both were fine.
She did a hock flexion test since he was short strided behind, but he passed it just fine.
The only other symptoms I have to go on are how he clearly labors to get up
hills and his temperature has been in the 98 range which is low for him. He's
normally around 100. Some research says that a low temperature suggests a chronic infection.
He has had hives all summer which he's never had before. I thought maybe this was all part of any allergy that's just wiping him out, but I have no way of determining that.
I am out of both money and ideas. Tufts suggested I bring him back up to see if he has an irregular heart rhythm while working, but I would think his recovery time wouldn't be that great if his heart was the problem. No diagnosis really fits. I thought of a respiratory infection, but that comes with a fever and nasal discharge. I was thinking ulcer, but he eats like a piggy and isn't at all grouchy or sensitive to the touch. If he tweaked something, I'd think I'd see lameness. The closest he comes to being lame is being short strided in back and he's built kind of straight back there anyway. I thought maybe heaves, but he's not coughing.
If anyone has any ideas, please spit 'em out before I pull all of my hair out.