I don't want my roommates to get another dog. They already have one dog stinking up the house.
Are you joking about the smell? Do you not like their dog?
No, it bothers me that the dog is loud and stinky.
Your roommates should've discussed this with you before deciding to get another dog. When living with a roommate it is always important to run by them important decisions.
I'm going to take this to the manager and make a big deal about it.
I would hold off on telling the manager until you've tried talking to them about the problem. If they insist on bringing another animal into the house you can see what the manager can do. You don't want to start involving the manager in disputes, because things tend to get out of hand like that.