اس دنیا میں جانوروں پر ظلم کیوں ہوتا ہے؟
Please see the discussion in the following thread: Discussion 48538
Since nothing explicit is mentioned in Quran regarding this, therefore there is no way for us to say anything with certainty. However, based on our observation, animals do have some sort of consciousness but unlike human beings, they do not possess congnizance of their consciousness the way we do. Therefore, on the outset, it appears that such reward may not mean anything to them the way it means to us.