@Jo *********
I agree and don’t deny deaths and injuries occur. Even people die on a very regular basis flying due to these same factors!
This is a valid issue and why the suitability of transporting a particular animal needs to be done on a case by case basis and avoided where possible.
At least where I worked the animal was assessed by a Vet before and after every sector. Time spent on the ramp (noisy/fumes) was also planned and minimised.
Temperature in the cargo hold (at least on the Airbus A320) is selectable and able to be set/monitored by the flightcrew. No doubt the case for other modern airliners.
Flight crew are explicitly made aware if animals are being transported and have procedures to follow when that is the case. Ive even seen live fish, birds and even bees loaded!
Never been in a cargo hold during flight but wouldn’t be surprised if it was quieter than the cabin due to the amount of bags. It still is insulated the same as the cabin.
Not trying to dispute you, just worked in the industry and know some of the dedicated teams who look after the animals at airports. They take their jobs very seriously.