If the animal is badly injured and needs to be killed, the Shariah allows it to be killed by means of Thabah. It must be slaughtered in exactly the same way as a sheep is slaughtered with the Tasmiyah as well. After Thabah, it may be sold to the zoo to feed the lions. If the animal is killed in any other haraam manner, then it will be maitah, hence selling it will not be permissible. Only after Thabah may the animal be fed to other animals. And Thabah includes the recital of the Tasmiyah even if the slaughtered animal is a donkey.