The total number of nonhuman primates in research in the United States was 71,921 in 2021 (the most recent year for which figures are available), according to the US Department of Agriculture. This figure does not include the 41,348 primates who were not assigned to research but were instead part of laboratories' breeding colonies.
Primate species in research include rhesus macaques, long-tailed (a.k.a. crab-eating or cynomolgus) macaques, stump-tailed macaques, pig-tailed macaques, squirrel monkeys, owl monkeys, African green monkeys, marmosets, baboons, spider monkeys, capuchin monkeys, titi monkeys, and others. Both wild-caught and purpose-bred animals are used, and in 2020 alone, 26,728 primates were imported into the United States, according to a veterinary medical officer at the US Center for Disease Control who presented these data in an online workshop of the National Academies of Sciences, Engineering, and Medicine on March 9, 2021. According to the same source, nearly half a million primates (~482,000) were imported to the United States between 2000 and 2020. Primates are subjects in studies involving toxicology, endocrinology, reproductive biology, neurology, behavior, cognition, genetics, and more, as well as the production of vaccines and medications for human diseases such as AIDS and hepatitis.
Historically, many of the basic physical and psychological needs of primates were ignored by those conducting research with them. There was an unfounded concern that modifying the barren environment would introduce data-biasing variables and that the financial costs to accommodate the animals’ needs would be too great. As a result, primates were typically housed alone, in small, barren cages.
In 1985, the Improved Standards for Laboratory Animals Act (ISLAA) amendments to the Animal Welfare Act were passed, mandating, among other requirements, “a physical environment adequate to promote the psychological well-being of primates.” The USDA, charged with enforcement of this requirement, however, was pressed by the biomedical research industry not to require that primates be housed in pairs or groups. As a result, even after the ISLAA amendments were enacted, most primates continued to be housed individually, with only an unused toy in the cage for “enrichment.” A 2003 survey by Baker et al. (published in 2007) found that only 46% of the indoor-housed primates used in research were housed socially, and 5% of those “socially housed” primates were given access to a conspecific only through a mesh barrier or only intermittently (e.g., overnight or between studies).
Today, nearly 40 years after the legal mandate to provide for the social needs of primates, the USDA appears to be increasing its diligence, pressing laboratories to socially house their primates. Further, the latest edition of the Guide for the Care and Use of Laboratory Animals (Guide)—which research facilities are required to follow if they are funded by the National Institutes of Health or accredited by the Association for Assessment and Accreditation of Laboratory Animal Care International—has undergone a dramatic philosophical shift in perspective that should benefit primates and other animals in research. The eighth edition of the Guide, published in 2011, calls for social housing and enriched cages, recognizing that providing these elements can reduce stress (itself a data-biasing variable) and lead to more reproducible results (better science) while improving animal welfare. In fact, socially housing primates is widely considered to be the most effective way to promote their psychological well-being. A 2014 survey by Baker (published in 2016) indicated that 65% of indoor-housed primates used in research were housed socially—a dramatic improvement from the 2003 levels, but a long way from the ultimate goal of social housing serving as the default housing scenario for all laboratory primates, as proposed in the Guide.
A humane ethic and improved scientific outcomes necessitate a look at the important behaviors of primates. They have a strong need for companionship—with grooming being a key social activity—as well as a need to experience agency, i.e., the ability to exercise some level control over their environment. Using positive reinforcement training (PRT) to encourage animals to voluntarily engage in husbandry or research activities (rather than by using force) is an important way researchers can increase primates’ perception of agency and improve their welfare. In 2014, all surveyed research facilities reported using PRT to some degree, but only a quarter of these facilities reported using PRT with at least 50% of their research primates. Climbing and perching are also important behavioral activities. The vertical dimension of the primate’s environment may be used for a variety of purposes, including rest and sleep, and to escape and feel safe from predators (in the laboratory, humans can be perceived as predators). Finally, primates require mental stimulation to avoid experiencing prolonged periods of boredom, which can have negative health consequences. Social housing, PRT opportunities, and environmental enrichment are all methods that can be used to enhance psychological well-being for captive primates.
AWI has been at the forefront of the push to improve conditions for primates in research. AWI worked toward the successful adoption of the ISLAA amendments in 1985, provided data encouraging significant changes in the eighth edition of the Guide, and has widely distributed extensive data on the needs of primates that by law and ethical obligation must be accommodated to the greatest extent possible in the research laboratory. AWI will continue to promote evidence-based improvements for the housing and handling of research primates and encourage the reduction and replacement of animals where appropriate.
“Jack” is a cynomolgus macaque who was discarded at an animal control agency after suffering severe neglect. (On the voluntary surrender form the former owner stated “UNWANTED" as the reason for surrender.) Jack is now safe and recovering at OPR Coastal Primate Sanctuary in Longview, WA. One of his favorite activities is to play in the macaque pool, an excellent form of enrichment. Video courtesy of OPR Coastal Primate Sanctuary.