I was really hoping for a better response than this.
Hello caincuttercraig ,
You ask a question that has so many variables it nearly impossible to give a finite answer.
My name is oldhounddog , I train and run coonhounds and currently have 10 dogs that I work. Of this 10 , all but one are trained on a regular basis. These are very high drive dogs and will easily push themselves beyond the threshold of normal limits and thus must be carefully handled. I have hunted from north Georgia down to the Griffin area below Atlanta and central Florida from Tamps to Cocoa in high heat.
For the most part dogs need to be conditioned to the weather they are going to work/hunt in , however , variables like extreme infrared heating expressed not only on the dog , but , the ground heat also builds up very fast in mid summer. So as you can see the dog is getting it from all angles , from above and reflected back up from sand and direct contact with ground too hot for you and I to stand on barefoot.
In practicle application , dogs must be cooled down every so often as to prevent internal heat build up. This requires supervision and hands on ability to recall dogs even if they are conditioned to extreme heat. So , keep lots of cool water on hand for dogs and keep an area in mind that has shade , and in the very extreme cases get the dogs in the truck with you and the a/c turned on. If you hunt them for an hour , cool them for an hour…..
I run Redbone coonhounds , and I can tell you without a doubt that hunting dogs with very high drive must be supervised b/c they will push to exhaustion and beyond.
Just my thoughts from the past 45 hunting seasons.
Good Luck , oldhounddog