Why are my dogs farting?

My dogs (9 mo. old doberman and 2 year old boston terrier) always fart. They don't eat human food (occasionally yogurt) and don't get into trash or anything. I've had them on 2 different kinds of food. Right now they are on Wellness (not a cheap food!) and fart almost every hour or so, and it's been going on since i got both of them. They are really healthy dogs with no other medical problem. The doberman poops a lot though, too.