This question, most likely, has the presumption of theistic evolution or at least 'old-earth' creationism, however answers without that presumption are welcome.
Suffering and pain exist in our world is because of sin (Isaiah 24:2-6 among others); presumably animals and the the entire created universe suffer the "groaning of creation" (Romans 8:19-22) because of sin. And we wait on the redemption of the world through Christ.
However, before the fall, or before humans even existed, there must have been countless animals and creatures who suffered horrifically (as many do today). Why were these animals allowed to suffer, as it seems they did, before sin had even entered the world?