Re: Harry/Cassandra
I know plenty about cows but we would need more space than we have. A single cow needs about one-and-a-half to two acres of land let alone field rotation to prevent overgrazing. If you want enough to feed the castle with milk, cheese, butter, and meat, you're going to need a proper herd.
And then maybe adding on sheep and other livestock. The castle grounds aren't going to be able to handle it - especially once there are students - and letting them roam the forest is out of the question.