When there is some disturbance caused by wild animals in a village or town, the police or others take action to kill them. Similarly, it is the duty of the government to kill at once all bad social elements such as thieves, dacoits and murderers. The same punishment is also due to animal-killers because the animals of the state are also the prajā. Prajā means one who has taken birth in the state, and this includes both men and animals. Any living being who takes birth in a state has the primary right to live under the protection of the king. The jungle animals are also subject to the king, and they also have a right to live. So what to speak of domestic animals like the cows and bulls.
Any living being, if he terrifies other living beings, is a most wretched subject, and the king should at once kill such a disturbing element. As the wild animal is killed when it creates disturbances, similarly any man who unnecessarily kills or terrifies the jungle animals or other animals must be punished at once. By the law of the Supreme Lord, all living beings, in whatever shape they may be, are the sons of the Lord, and no one has any right to kill another animal, unless it is so ordered by the codes of natural law. The tiger can kill a lower animal for his subsistence, but a man cannot kill an animal for his subsistence. That is the law of God, who has created the law that a living being subsists by eating another living being. Thus the vegetarians are also living by eating other living beings. Therefore, the law is that one should live only by eating specific living beings, as ordained by the law of God. The Īśopaniṣad directs that one should live by the direction of the Lord and not at one’s sweet will. A man can subsist on varieties of grains, fruits and milk ordained by God, and there is no need of animal food, save and except in particular cases.
Ref >> Srila Prabhupada Vani.