Animals can surely assess and "feel" quantities via the senses and via their own automatic body reactions (hormones etc...). As well as have many pre-programmed quantities in their genome.
But a "number" is purely an abstract concept. I don't think we can ever be sure an animal is actually "counting" things. Instead from what we know about how fear, excitement, etc is regulated via hormones it seems fairly probable that they are simply seeing, hearing, touching and this triggers a feeling that guides them to a certain behavior (through hormone secretion).