I have no clue. But back when there was a Hostess Outlet in town and I'd buy racks of the week old bred, bagels, etc., which would occasionally include chocolate chip muffins, chocolate cupcakes, Zingers . . . I asked my vet if it would be okay to feed them to the cows since I knew chocolate was toxic to dogs. Clearly, these products weren't pure chocolate and cows aren't dogs, but he said it's probably best if I didn't. He didn't have a definitive reason why, but better safe than sorry. As for chocolate milk? Personally, I wouldn't and see no benefit.