I think it is an age thing. (His getting offended when you say anything about this habit, I mean.) We all have difficulty accepting that we are not as young as we once were and most men at any age tend to become grumpy if you suggest there might be something wrong that necessitates going to the doctor.
You have two options, IMO. A full blown row because you insist that he consults his doctor to make sure nothing serious is wrong, or grin and bear it to keep the peace.
No consolation to be told it could be worse, is it? but my father developed the habit of passing wind, irrespective of whether other people were present or not. He insisted he did not need a doctor, (he was one himself, which didn't make it easier to get him to consult one).
This bad habit drove my mother mad, but she had to grin and bear it.
Hope your husband sees sense. Could you just revert to goat's milk and clear all cow's milk products out of the house`? That might do the trick.
That's three options, I never was good at counting!