If God Cares About Animals, Then What About Animal Sacrifices in the OT?

I am presently writing a book about animal suffering tentatively titled: The Darwinian Problem of Evil: Christianity and the Problem of Animal Suffering (four chapters so far!).

I think this particular problem of evil is the most serious one for believers. I'm also looking at what the Bible says about the treatment of animals and the various theistic responses to this issue. Think about just one thing. The Bible commands animal sacrifices in the OT, and for some national ceremonies we're told thousands of them were sacrificed, and done so gruesomely. But then we read in the book of Hebrews that these sacrifices never helped take away any sins. So God purportedly had his people slaughter animals for no good reason at all. Is this a God who cares for animals? No, not on your life, and that's just one thing we find about the treatment of animals in the Bible, and that's just one aspect to the whole problem of animal suffering.