In fact, [intellectual substances - that is, in the present context, primarily us humans] are said to be providentially managed for their own sake, and other things for their sake, in the sense that the goods which they receive through divine goodness are not given them for the advantage of another being, but the things given to other beings must be turned over to the use of intellectual substances in accord with divine providence.[SCG, III, 112, 10-12].
 Hence it is said in Deuteronomy (4:19): "Lest you see the sun and the moon and the other stars, and being deceived by error, you adore and serve them, which the Lord Your God created for the service of all the nations that are under heaven"; and again in the Psalm (8:8): "You subjected all things under his feet, all sheep and oxen, moreover the beasts of the field"; and in Wisdom (12:18) it is said: "You, being Master of power, judge with tranquillity, and with great favor dispose of us."
 Through these considerations we refute the error of those who claim that it is a sin for man to kill brute animals. For animals are ordered to man's use in the natural course of things, according to divine providence. Consequently, man uses them without any injustice, either by killing them or by employing them in any other way. For this reason, God said to Noah: "As the green herbs, I have delivered all flesh to you" (Gen. 9:3)
Now as is clear from what he says in 12, the fact that animals exist for our sake does not mean that we can use or abuse them in just any way that we wish. God cares about them, too (though obviously not in the way that he cares for and about man).
And shall I not spare Ninive, that great city, in which there are more than a hundred and twenty thousand persons, that know how to distinguish between their right hand and their left, and many beasts? (Jon. 4:11)God did not send Jonah to Nineveh exclusively for the sake of the people that lived there (though obviously that was the major reason); he sent him also for the sake of the animals that lived there, and who would be subject to the same judgment as the rest of the city.
Our care and concern for the animals ought to reflect our gratitude to God in giving them to us; to neglect or to abuse them is to show contempt for the gift that God has given. But this does not mean that we may not use them for our benefit.