Ensure the Flt Deck know that there is a dog in the hold so that they heat it. I know it should be on the manifest but it is sometimes missed. Just a polite word with the cabin crew would suffice.
Wasn't there an incident with BA a few years ago where there was a dog in the hold and the air-conditioning for the hold went u/s and the captain asked for votes to turn back or not? They did, and it was good (but expensive)
PR.