Reinhardt, V., Rossell, M. 2001. Self-biting in caged macaques: Cause, effect and treatment. Journal of Applied Animal Welfare Science 4, 285-294.

In the United States, there are an estimated 15,000 individually caged macaques. If 10% of these animals exhibit visible injuries resulting from self-biting and another 10% show unnoticed self-biting behavior, then about 3,000 animals (20%) are affected by this gross behavioral pathology. It stands to reason to assume that these 3,000 individual have no scientific value because research data collected from them are confounded by the animals' high emotional disturbance and hence cannot be considered scientific valid. [p. 290] "The frequent occurrence of self-biting in individually caged macaques is an alarming sign that the housing conditions are not appropriate. In order to prevent the development and reduce or eliminate the occurrence of self-biting in caged macaques the animals inherent social needs must be addressed with much greater consistency. No exemptions should be granted - except for veterinary health-care reasons - to the rearing and housing of primates in species-appropriate, compatible social settings. Serious efforts must be made to remove the avoidable pain and distress resulting from pathological self-biting, in the interests of both animal based science as well as animal welfare."