Is it a sin to mistreat animals?

The Catechism of the Catholic Church cites the creation account and God’s words to Noah and his sons in Genesis as the scriptural background for its teaching about animals. God says to Noah and his sons,

The fear and dread of you shall rest on every animal of the earth, and on every bird of the air, on everything that creeps on the ground, and on all the fish of the sea; into your hand they are delivered. Every moving thing that lives shall be food for you.... (Genesis 9:2-3)

Against that background the Catechism states that it is legitimate to use animals for food and clothing, to domesticate them to help in human work and leisure. It is morally acceptable to use animals within reasonable limits for medical and scientific research or experimentation, it says. At the same time humans owe animals kindness. It is contrary to human dignity to cause animals to suffer or die needlessly. While animals, along with mineral and vegetable resources, are entrusted to the stewardship of human beings, our dominion over them is not absolute and requires religious respect for the integrity of creation. The Catechism also says we human beings owe animals the kindness and gentleness shown them by saints such as Francis of Assisi and Philip Neri (2415-2418).

Dominican Father Philip Boyle has addressed the question of animal rights. He argued that there is a qualitative difference between humans and animals:

If qualitative considerations are not allowed to distinguish among species, the unqualified reverence for life might require us to go to the absurd lengths of protecting bacteria against penicillin. Limiting legal rights to human beings is not unreasonable, because laws are made by humans for humans.

Father Boyle wrote further,

Framing the issue in the language of “rights” for animals i creates an ethical quagmire. Responsibilities toward animals in research should be based not on the rights of animals, but rather on the responsibilities that humans have toward other beings.... Ethical theory acknowledges the legitimate use of animals while also accounting for the deeply held concerns that animals not be abused or mistreated.