You must read through the US Public Health Service Policy and the National Academy of Sciences Guide to understand animal care and use. Notice that the Guide closely follows the Policy and extends it in some ways. The Guide is an interpretation and commentary on the Public Health Service Policy on Humane Care and Use of Laboratory Animals, which is the the authoritative regulatory document on this subject. As a practical matter this orientation will concentrate on the Guide.
The Guide makes relatively easy reading of the more fundamental documents: the Federal statutes and USDHHS policies and other materials from which much of The Guide is composed. Many of these fundamental documents are also available by selecting the "Resources" link below.
The second thing to notice about The Guide is that it is NOT comprehensive. One must use other documents and resources to answer questions and devise protocols for the use of laboratory animals. Agricultural animals, microscopic animals, and alternatives to using animals are not covered in any depth or with the same authority. Please read widely in the documents listed under Resources below.