Around this time every year my rabbit, Joey, starts to become ill. before I just thought it was him catching a cold off me as each time it's when I'm ill as well but thumper my other rabbit has never become ill before but this year he has. It seems like it is just the common cold and it is the first winter that they have been put inside but how would I prevent the colds for my rabbits?
Rabbits don't catch the cold, chances are your thinking of "snuffles" (aka pasteurellosis) which most rabbits carry but not everyone shows symptoms (stress or immunosuppression can reveal the illness). If Thumper is housed with Joey then Joey is the one who passed it to Thumper, chances are these flare-ups will always reoccur. If it gets too bad veterinarians will prescribe antibiotics (such as enrofloxacin) to clear it up.
I would recommend that during the colder months to house them indoors since it seems to be a contributing factor.
If you get any new bunnies do not house them with your current rabbits, pasteurellosis is very contagious.