Heat INtolerance?

Curious as to whether others have experienced an increased intolerance for hot weather (particularly while exercising) in their dogs and what the suspected cause was?

Bus is 9 1/2 years old now, and still as active as ever, but I've noticed over the last year or two that his tolerance for heat is significantly decreased when exercising. He's been examined by multiple vets and had a normal CBC/Chem last year after I decided his problem was not a one-off episode, he looks as healthy and fit as ever, but I've not experienced this with any other dog, and feel like it can't be normal.

Current temperature here is 79, and humidity is around 60% ... I took him into our partially shaded backyard while I did a few things, and he found a ball so I threw that for him a couple times, then fake threw it so he'd search for it (I've taken to doing this in warmer weather because it leaves his mouth open to pant freely, rather than having a ball in it), after maybe 2 minutes I noticed he was starting to pant moderately, and called him to go in. He grabbed the ball, which I took, then on the way up found another ball, which he picked up, ran around with for a few seconds, tried to take into my mom's pond, then brought back to try to get me to throw. I called him off it, but as he let it go, he had an episode where his legs and neck became rigid for a second or two, it looked like he had a brief strong tremor even (seizure? it was so quick), and plunked down into a sloppy sitting position like his hind legs were weak. He looked confused by what was happening, but immediately after, tried to grab the ball again. I dipped his feet/legs in the pond, then took him in to my parents' house (AC on). He wasn't even panting after we got inside, but did lay on the hard floor rather than a bed initially (cooler). The total time we were outside was maybe 10 minutes, and I had my grandmom's dog out with us on a leash and she wasn't even panting.

The first time he had an episode like this (last spring), it was around 75, low humidity, early spring weather. That time, we had played ball in the yard for about 15 minutes, and he was panting pretty hard, but not moreso than was typical for him after playing ball (something we were doing every day at that time). We were walking up to my house, and he randomly started stumbling, walking in a drunken fashion. I scooped him up and took him into the bathroom to hose off, and when I stood him on the floor to turn the water on, he was fine.

Since that day, I've been pretty careful to limit him to cooler times of day, and generally let him in the water before we even play/multiple times while and he does fine, though if he can't get wet we can only play for very brief periods. It's gotten to where I'm afraid to take him for walks on warm days because I'm concerned he'll overheat and I won't be able to get him cooled off. I wasn't expecting it to happen so quickly today, and it seems like as time goes on, it takes less time/exertion to cause a problem. One of the things that gets me is that when we come in, even the two times that he's had problems, he doesn't act like a tired or hot dog. He's trotting around, hoovering things off the floor, pants only briefly if at all, etc.

I've had multiple dogs that liked to be active outside, and never had one with this issue. My other dachshund (until her vision deteriorated to the point where she couldn't see the ball well enough to chase) could play fetch for hours on a day like today, without issue... maybe she was the anomaly? I've wondered if he could have EIC, but he's never had a problem when it was below 60 degrees (making it a heat related issue?), and I don't think it's known to occur in dachshunds. I don't really know where to go from here- I'm thinking about going for a cardio consult, but don't really want to spend $500 chasing a maybe.

The episode you describe sounds very much like a number of seizures I've seen, I would call your vet and describe it, and if happens again, try to get a video. Seizures can definitely be triggered by overheating and get worse with age. Medication might help or you may just need to closely monitor his heat exposure and exercise.

I'm no vet, but I'd bet that that's what's going on. The vet will be able to confirm that, try to pinpoint the cause, and come up with a plan for managing it.

That was my first thought as well, but it wasn't exactly like other seizures I've seen, he looked aware and bewildered that his body was not doing what he was wanting it to do, and it was only one big "spasm", then he was normal again. Weird. I work at a vet hospital, and am hoping to get a chance at some point this week to run him then have them listen to his heart on the offhand chance that there's something going on that's exacerbated by exercise, and they might hear something abnormal. The last time I had him checked, the drs attributed it to just overexerting himself in warmer temps, and said he might have decreased tolerance due to age, but he doesn't agree with slowing down! If they suspect its seizures, I'd rather not put him on meds if it can be managed without, so I guess if everything checks out again, it'll be a matter of monitoring for more episodes and managing to try to avoid them. Part of me is still holding out hope for a silver bullet that would "fix" him, but it's looking more like it's going to be continuing problem.

On the plus side, his coat is shiny and skin is great from swimming in the swamp every time he exercises (I used to rinse him off after, but it dried him out and made him itch)- he gets compliments all the time- on the downside, he usually smells like a stale crab and every (stinky) dog bed has a little pile of sand/dirt in the middle of it from him :< Oh, well. I may try getting a super small kiddie pool for him, he usually knows when he needs to cool off and either heads to the creek or my mom's pond, so maybe that would be a compromise- slightly less gross for us, still cool for him

I was going to suggest Exercise Induced Collapse, but then I saw that your little guy is a Dachshund