Question
Is there a specific verse that requires that we do not cause an animal unnecessary pain?
Answer
The Torah states (Exodus 23:5) that if we see an animal struggling under its load, we are to assist the owner of the animal in unloading it. In the Talmud there is a difference of opinion as to whether or not we should take this as a general Torah mandate not to cause cruelty to animals. Even if there is not a Torah mandate, however, all agree that at the very least there is a Rabbinical mandate not to cause pain to animals unnecessarily.