As illustrated in the classification schemes listed below, there can be overlap among various species classifications based on the intended purpose for use by humans. One important classification of animals by U.S. regulatory agencies is the classification as a MAJOR SPECIES versus a MINOR SPECIES. The major species group is comprised of seven animal species that are highly prevalent and in high demand in the U.S., whereas the minor species group includes all other (non-major) animal species.

Governmental regulatory agencies with oversight of animal species have authority to regulate many aspects of animal uses, medical care and husbandry depending on the intended use(s) or individual animal species. Companion animals, which include all species used for human companionship, entertainment, service, psychological support or other similar purposes, are subject to a lesser degree of government regulatory oversight compared to animals used for production. In general, production animals, which include animals (cattle, sheep, goats, swine, poultry (including egg-producing poultry), equine animals used for food or in the production of food, fish used for food), are subject to a greater degree of governmental regulation and oversight.