From the Catholic Encyclopedia article "Cruelty to Animals," a quote from Cardinal Manning, in which he says that man must show mercy to animals, not for their sakes, but for our and God's sakes:
It is perfectly true that obligations and duties are between moral persons, and therefore the lower animals are not susceptible of the moral obligations which we owe to one another; but we owe a seven-fold obligation to the Creator of those animals. Our obligation and moral duty is to Him who made them and if we wish to know the limit and the broad outline of our obligation, I say at once it is His nature and His perfections, and among these perfections one is, most profoundly, that of Eternal Mercy. And therefore, although a poor mule or a poor horse is not, indeed, a moral person, yet the Lord and Maker of the mule is the highest Lawgiver, and His nature is a law unto Himself. And in giving a dominion over His creatures to man, He gave it subject to the condition that it should be used in conformity to His perfections which is His own law, and therefore our law (The Zoophilist, London, 1 April, 1887).
From Moral Theology: A Complete Course Based on St. Thomas Aquinas and the Best Modern Authorities by McHugh, O.P., & Callan, O.P.:
- The Killing of Animals (or Vegetation).—(a) In itself, the killing of animals is not sinful; for animals are made for the use of man. Hence, it is lawful to kill, not only harmful animals, such as those that prey on human beings or breed pestilence or destroy property, etc., but also other animals, when their death is necessary for some good purpose, such as the provision of food, clothing or medicine for man.
(b) In its circumstances, the killing of animals may be sinful, and even gravely sinful, as when one kills the animals of one's neighbor (Exod, xxii. 10, 11), or hunts against the law, or injures society by prodigal destruction of animal or plant life, or kills animals in cruel ways. The skinning of animals alive, in order to secure finer-looking furs to satisfy the vanity of women, is an inhuman barbarism of the worst type that should be reprobated by everybody.