BigGameHoundsmen.com

i picked up some bounce back electrolyte supplement for horses at the feed store been water the dogs with it the night before and after a race seems to be helping the dogs stay on the bears that wear nikes longer then ever before and seem to recover faster any one else use anything like it. it was cheap 12$ for 4 lbs uses two tble spoons per cup of water 4lbs last alomg time .

Pedialyte, its for kids but I gave it to a hound of mine that was dilusional,vomitting and pissing/puking blood and foaming at the mouth after a real long bear race. Temps suddenly climbed literally 10 degrees in a matter of an hour and it got unbelievably humid, I knew they were in trouble but couldnt get them back and he was the last one like always.
Thought he was going to die but small doses of that over night and eventually raw elk 24hrs later and he was ok.
Looking back though I figure it was a combination of dehydration and internal injuries from a real mean bear but I keep a bottle of it around now...

I am going to give that a try because this same dog seems to get effected from the heat a bit easier now and often 8 hours later he looks like he's lost 10lbs after a serious race, sounds like what you mention may be a solution to try for him in warmer weather.