The main federal law protecting animals in the United States.
Among other things, the AWA applies some minimal protections to certain species in research facilities, including universities and colleges, nonprofits, hospitals, corporations, and government agencies. Secondary educational facilities (e.g. high schools) and American-owned facilities operating outside the US are exempt.
The AWA notoriously doesn't apply to all animals used in labs. While it does cover dogs, cats, primates, horses, ferrets, pigs, goats, hamsters, Guinea pigs, and most other four-legged mammals, plus marine mammals, it does not apply to:
- Lab mice (genus Mus) and lab rats (genus Rattus) specifically bred for experimentation, which are estimated to be more than 90% of all animals being held in labs. (However, the AWA does apply to all other mice and rats, including deer mice, dormice, wood rats, etc., which are rarely used in research.)
- Birds specifically bred for experimentation. The problem here is that no one has ever figured out what birds "bred for use in research" are, so no implementing regulations have been created. Because of this, for all practical purposes, all birds are unprotected.
- Reptiles and amphibians
- Invertebrates: fish, cephalopods (e.g., octopus), crustaceans, insects, worms, etc.
- "livestock or poultry used or intended for use for improving animal nutrition, breeding, management, or production efficiency, or for improving the quality of food or fiber."
The Animal Welfare Act and Regulations [PDF]:
https://www.aphis.usda.gov/animal_welfare/downloads/bluebook-ac-awa.pdf
P.S.: Besides animal-experimentation facilities, the AWA also regulates exhibitors (e.g. zoos and circuses), breeders (e.g. puppy mills), and transporters of animals. It doesn't regulate retail businesses ("pet stores"), farms, slaughterhouses, or racetracks.