I seem to recall a story by either Silverberg, Sturgeon or Farmer
that dealt with almost precisely that--only it was a "universe next
door" story, not a future shock story. But they weren't grown without
brains--just bred for stupidity and had their tongues surgically
removed (at weaning?). Protagonist falls in love with a heifer, has
to deal with the fact that, nature or nurture, she's got a
single-digit IQ and nothing he can do will change that now.
Oh, and human dairy products are a commodity, too.
A stirringly grotesque story, which is why I think Farmer wrote it,
but it's about misplaced love, which is why I think of Sturgeon.
Silverberg is a candidate because for a while there in the 60's he
was as outrageous as anyone at the time.
MMB, at but not for OCC