I wish my bf was that interested in pets!
but to address your real issue, maybe you can let him make the decisions about the dog when he is the one doing the activity. (i.e. he takes him to the groomer, he can decide on his cut, etc). I agree with you about the food thing though, because that's a health issue. and, I agree with the other posts about having to compromise.
On a different track though, I know sometimes people will go off about something, but may be concerned or upset about something else or a deeper issue. (I watch Dr. Phil sometimes
and he says sometimes people fight about the "symptom" and not the "issue") idk...this is only my observation though...