How should we treat animals?

I kill mosquitos and flies indiscriminately
I eat chicken, fish, cows
The things I never do to cats, dogs, hamsters
And i would never want to get close to snakes, wasps, alligators, crocodiles, centipedes...
Yes this is a double standard..but i don't care

And if they do something bad, just hit them and play with them every day, feed him and etc
poor animal.. getting hit..

If we test medicine on a rat, that does not mean that it would work on humans as their bodies work differently. Nevertheless, if we do it on a human, it is different because (from a Christian point of view) we are made in God's image and animals are not. Interesting question.
How should we treat animals?