We have 2 mini doxies, ages 4 & 3 1/2, not blood related, but both full blooded. In the past 2 months they have started expelling gas almost constantly. They have been on Science Diet since birth, but we do also give them daily "rewards/treats". Is this gaseous condition normal?

How much gas different dogs put out varies. I don't think it would suddenly increase for no reason after 3-4 years. Has anything at all changed, a new neighbor throwing treats over fence, something new to forage, etc. Can you compare the list of ingredients on an old and new bag of the Science? If you can't identify any other changes, see if your vet can find anything.