Because the cow has the udder
An Easter bunnet!
Having legs!
The farmers milk them dry.
Because he higher and higher. (I translated the joke from Dutch, and yeah it's supposed to not make any sense, it just sounds funny, in Dutch at least. :-$)
Because they lactose I don't know why I found this so funny! ready for the down vote to begin 3
Soy milk.
Because the cow has the utter.
He was sent to the udder side