Bratcher, N., Clemons, D., Medina, L. 2012. History of enrichment in the ILAR Guide for the Care and Use of Laboratory Animals. Enrichment Record 12, 10-12.

Throughout the nearly 50 year history of the Institute for Laboratory Animal Research (ILAR) Guide, little attention or content was allocated to the subject of enrichment until the current (8th) edition (NRC 2011). Although animal wellbeing, social environment, psychological well-being and behavioral adaptation have been mentioned in previous editions, guidance on catering for these was not provided. For instance, the 4th edition (1972) refers to physical comfort and well-being, and also to the potential for "psychological discomfort" due to confinement and/or lack of exercise, but enrichment was not specifically discussed in the Guide until the 7th edition (1996), where 4 index entries were devoted to the subject. In the 8th edition, however, there are 22 index entries and dozens of references on environmental enrichment, as well as many more in related areas such as socialization and behavior management.