Pure meanness of the part of the birds. A combination of these factors is usually involved in any outbreak. Some cannot be corrected even though you know they are involved. Birds usually do need to be moved from the brooder house to growing facilities, and in some cases, moved a third time into laying quarters. If a nervous breed is purchased, you have to live with the problem, at least until the birds are marketed.
Temperature control is expensive and sometimes impossible.
A nutritional deficiency or a disease is sometimes very difficult to detect and, at best, considerable time is required to make these kinds of determinations. In the meantime, the birds may have devoured each other. To make matters worse, if an outbreak occurs and one or more corrections are made, the outbreak may continue. Once the habit is started, it is often too late for effective management changed with the affected flock. Perhaps the most frustrating thing about cannibalism is that management may be near perfect and outbreaks still occur.