How many animal abuse cases are reported per year?

Thousands. I work at an animal shelter myself, and in just one year we had just under 1,500 animals adopted from one local shelter. This number includes all kinds of animals from all kinds of backgrounds.

One can only assume an animal has been abused by the physical conditions and reactions of the animal unless there was proof.

There are many types of abuse as well. A lot of people think that physically hurting an animal with force is the only type of abuse, but neglect is also a form of abuse as well in which case that is the majority of animals that end up in a shelter. Very few animals come into shelters from loving homes. People stretch the truth to their reasoning for animal surrender so you'll never know the real story or background of an animal unless there is proof.