A lot of it is turned into processed meat and sauces (burgers, sausages, jars of pasta sauce). A lot of what is left over after that actually becomes animal feed again! Since BSE (mad cow disease) we need to feed animals to different animals though, so we no longer feed cows to cows, but e.g. turn cows to pig or dog food.

The parts which are thrown away are usually mandatory for hygienic reasons. The spinal column, remaining gut contents, ...

Source: worked at a pig abattory.