Ba Ba from a sheep

Na Na from a horse

hernias are fun they smell like cows that go moo moo oink

Oink, or other farm animal sound that fits your crossword )

The sound that a pig makes sounds like "oink". The sound a cow makes sounds like "moo". These are farm animals.

No, never. Pigs don't even say "oink," rather "oink" is a poor onomatopeia-choice for how pigs grunt, squeal, snuffle or make similar sounds. In the matter of onomatopeias for cows, though, it's common "knowledge," especially among children, that they say, "moo" rather than "oink."