I have. Extremely intelligent might be a stretch, but a little. Certainly curious, emotional and social. Id rate them at the level of cats, dogs and pigs. My cat is dumb as fuck, no way she could outsmart a cow.

Dogs and pigs can be trained.

Cats can, to a certain degree.

Cows? Not so much. I wouldn't rate them at the same level as cats, dogs and pigs (source: farming background).