Should animals have a bill of rights written into law?
A bill of rights is not necessary. Our faith provides us with all the guidance we need on this question. Without endorsing the notion that animals possess rights, the Catholic Church nevertheless provides a basis for moral constraints on the treatment of animals. The Vatican II decree, Gaudium et spes (no.26) reminds us that humans possess "universal and inviolable" rights to everything necessary for living truly human lives. However, proponents of animal rights have advanced similar moral claims on behalf of animals, especially in the areas of recreational hunting, blood sports, and the marketing of furs. I believe this is less a consideration of whether or not animals have rights, per se, and more a question of the moral constraints placed upon humans in their treatment of animals. Here we we must distinguish between humans and animals.
In the Book of Genesis (2:19-20), we read that God entrusted animals to the stewardship of humanity, whom he created in his own image. Animals are Gods creatures and while we were given dominion over the earth and all its contents, we do owe animals our care and kindness. We may legitimately use them for food and clothing. They can even be domesticated and used by humans for work and leisure. The Catechism of the Catholic Church, in number 2417, tells us that they may also be used in scientific and medical experimentation, which is morally acceptable, as long as this "remains within reasonable limits and contributes to the caring for or saving of human lives".
Nonetheless, we must remember that the seventh commandment demands respect for creation in its entirety. Our dominion, therefore, can never be seen as absolute. It is limited to a sincere respect for the integrity of all creation, thus ensuring the proper treatment of all animals.