The Catechism of the Catholic Church states that we can use animals for 'just reasons', but how can mistreatment of animals truly be just? They may not have rational souls, but they are sentient and they still suffer from distress; they also show love and other emotions. There are plenty of good alternatives to food, clothing, testing of products, and entertainment, so how can we say that the usage of animals for these purposes is 'just'? We don't truly NEED animals for food -- vegan diets are nutritionally adequate on their own -- or for any other purposes. The treatments of these animals are just being used to fulfill our sensory pleasures and other selfish reasons. Just because God gave us dominion over the animals does not mean we should harm them -- we should take care of them. How can the Church justify the animal cruelty when we are called to be compassionate people? Shouldn't the Church at least say that buying free-range products would be more morally acceptable than animal by-products of factory farming conditions?
The following links should help answer your questions about the just uses of animals. If you have any further questions, please contact Catholic Answers directly.