The Animal and Plant Health Inspection Service (APHIS), an agency within the U.S. Department of Agriculture, contains several divisions overseeing plants and animals in agriculture, commerce, etc. One of those divisions, APHIS Animal Care, is in charge of enforcing the Animal Welfare Act, which among other things, regulates the use of animals in laboratories. (Animal Care's other main responsibility is enforcing the Horse Protection Act, which protects only walking horses, not racehorses.)
Among other things, APHIS AC inspects all research facilities when they apply for registration and usually once per year after registration (sometimes more often if a facility has violations). APHIS also requires that all registered facilities send in an annual report of their animal usage (covering AWA-protected species only).
It's very common to hear APHIS Animal Care referred to simply as "APHIS" or even "the USDA" in documents, websites, and other material about animal experimentation.