Over abundance of food does not mean quality food. What is their main staple diet?There is an overabundance of food and I give treats of carrots, lettuce, apples, raisins and waffles!
Mice are more prone to cannibalism than than rats however here are some of the top reason for cannibalism.
Low quality food (low protein food with fillers that have zero nutritional value)
Lack of water
Overcrowding
Stress