Facebook has options for reporting posts, pages, and groups.  When reporting a picture it is possible to cite animal abuse as an option, but not for a whole page.  There are plenty of groups/pages out there advocating for harm and torture to be caused to animals, and even when reported for all kinds of reasons it is within Facebook's guidelines so they won't remove them.  They need to stop being complacent with animal cruelty and help the spread of these hateful groups and pages.