Research conducted on primates spans a wide range of fields including human pathologies and diseases (such as AIDS, hepatitis, and Ebola), psychological disorders, toxicology, xenotransplantation (primates and pigs are the species primarily used as cross-species donors), product safety testing, dentistry, biological warfare, drug abuse, vaccines, Parkinson’s disease, cloning, and many more. Animals are burned, isolated, food deprived, water deprived, poisoned, and irradiated. During research on such human diseases as AIDS and Ebola, monkeys are infected with various virus strains and combinations and given test vaccines; disease progression is observed without intervention until the monkeys finally die. Some monkeys are scheduled to be killed, or “sacrificed,” at a certain point in a research protocol.

Since the 2001 terrorist attacks on the United States, funding for research to create vaccines and treatments for bioterror agents (such as anthrax, smallpox, botulism, and nerve gas) has increased dramatically. For many researchers, the test subject of choice is the monkey. [1]

Indoor single housing



Title 9 of the Code of Federal Regulations (9 CFR – the USDA regulations that provide the nuts and bolts of the Animal Welfare Act) dictates the sizes of cages for nonhuman primates. For example, a monkey weighing 3-10 kilograms (6.6-22 pounds) is only required to have 4.3 square feet of floor area, and a height of 30 inches. [2] In our experience, research labs do not usually exceed the cage size standards required by law.



Infant monkeys can be housed in isolettes (similar to an incubator), if they are very young, and in cages of 4 square feet in size if they do not require the warmth and protection of the enclosed isolette. Infant monkeys are used in invasive research just as adults are. They can be single-, pair- or group-housed, and cages can easily be modified and connected to one another.

Stainless steel cages built for individual monkeys are similar in laboratories all around the world. The configuration of the door or the squeeze-locking mechanisms may be different, but all cages are built with three major considerations in mind: ease in cleaning, access to the monkey, and the ability to fit more animals into a room. The typical cage is enclosed on three sides; the top, bottom and front are made of bars. The bars on the top and bottom are either straight bars, or a checkerboard of woven steel wire.

In cages with the woven bottom, it is not unusual or unlikely for bits of desirable food or treats to fall through the cage floor and land in the inaccessible urine pan just inches below the cage bottom. It is also not unusual for a monkey to get her hand stuck in the mesh while trying to retrieve the treat from the pan, the monkey will squeeze her hand through the flooring but once she’s grabbed the food, she may refuse to let go. The harder she tries to get her hand back through the cage floor, the more swollen her hand becomes and the less likely it becomes that the hand will fit back through at all. When the monkey is finally found in this condition – working furiously and desperately to free her hand – if it will not slide out with the application of a non-toxic lubricant, she is further traumatized by being lifted off of the rack and having technicians break the cage’s bars with a bolt cutter.



The solid cage sides allow for easier cleaning, and also protect the hands, fingers, and tails of monkeys whose cages are in close proximity to each other. Cages for individual monkeys are often mounted on rolling racks, holding four cages (two above and two below), and pans placed beneath each cage to collect waste. Cages can also be mounted on a wall rack, with a long trough under them to catch waste (some labs are equipped with automatic washing systems which routinely flush waste from the troughs). Cages in close proximity allow monkeys to squeeze a hand out between the bars, and grapple with the hand of a neighbor (it is not infrequent for fingertips to find their way into a neighbor’s mouth, and be bitten off). Monkeys in individual cages have been known to engage in affiliative behaviors by reaching out and holding the hand of a neighbor, which is the most amount of physical contact they can get. This may be the only contact with conspecifics (individuals of the same species) that a monkey will have for most of his life.



The doors to the cages usually either slide upward or sideways. Special transfer boxes fit to the doors so that unanesthetized monkeys can be quickly removed from their cages. Most monkey cages are fitted with a ‘squeeze back.’ The squeeze mechanism is a false back/wall that can be pulled forward in order to press or restrain the monkey at the front of the cage. A monkey is usually squeezed when an injection is required, or when she refuses to jump into the transfer box.



It is legal for two monkeys to be caged singly in the same room and in the same rack so that they cannot directly see each other – as long as there is a mirror on the wall across from them so that they can see each other’s reflection. More typically, 10-30 monkeys are kept in windowless, cinderblock rooms. Monkeys of several species may occupy one room.

Monkeys living on the bottom row of cage racks have the further disadvantage of being deprived of light. It has been argued that monkeys living in a lower row cage exhibit more stereotypies (abnormal behaviors) and are less physically active than monkeys living in the upper row. [3]



There is an abundance of research that indicates that single caging (the housing of one monkey or chimpanzee alone in a cage) is stressful, causes deleterious effects, and results in stereotypical behaviors such as pacing, circling, hair pulling, rocking and self-biting. Institutions are required to house primates socially whenever possible and provide justification if single instead of social housing is used. [4] The standards for justifying single housing are relatively low, and it can be a simple matter for a researcher to convince the Institutional Animal Care and Use Committee (IACUC) to exempt a monkey or a group of monkeys from the social housing requirements. However, there are institutions that house primates in single cages without scientific justification.

Indoor and/or outdoor social housing

Some monkeys are housed in pairs. Their cages may actually be two smaller cages next to each other in a rack, with the solid sides cut out to allow the cages to connect. Some of these double cages are equipped with sliding partitions, which can be used for breeding purposes. If a female is required to reproduce, either she or the male can be moved to the empty half (the mate is locked over, using the partition) of the double cage and the partition is then removed to allow access. These breeding pairs will remain together for a few days to ensure that the female has become impregnated.



‘Gang cages’ allow a group of monkeys to live together; gang-cage groups usually consist of only one male each. Their quarters may be one large cage (for example an 8x10x8ft room), but can also be several smaller ones tunneled together. Some facilities have buildings with runs or rooms, each with a ‘corn crib’ style outdoor enclosure. Sliding doors allow the workers to separate group members or lock them inside or out. These housing conditions usually only have a few perches and/or swings and are typically crowded.

‘Runs’ (named after enclosures in which dogs would typically be kept – some facilities actually convert dog runs into monkey housing) also allow groups of monkeys to live together. Runs can come in various shapes and sizes and often consist of cinder block, chain link and some perches. These enclosures are also typically crowded. Some facilities use runs as a temporary housing location, for example as part of a weaning process when infants are removed from their groups and prepared for research.



Finally, some facilities house multimale-multifemale groups of up to or greater than 100 monkeys in ‘corrals’. Corrals can cover up to one acre of land, are enclosed with 15-foot high metal walls and typically include climbing structures. Corrals may also have an indoor area that is heated during the winter months. Some facilities do not provide an indoor area and, at times, the monkeys are exposed to temperatures below freezing during the winter.

Corrals will typically house breeding groups, but members are often removed from the group for sale to another research facility or to be assigned to a specific research protocol at that institution. Overall, corral housing enables more ‘normal’ group living in comparison to single cages, runs, or gang cages, and the animals are exposed to grass and sunshine. But there are still several captive stressors associated with corrals, including unnatural aggression like maiming lower ranking family members, including youngsters, and social overthrows (a power shift by attacking the alpha family to the point of death if they aren’t removed). In the wild, targeted individuals would not be subjected to relentless aggression since they could either escape the immediate area or groups can split if the alpha family is challenged or a group gets too big. In corrals, even though there is more space than a cage or a run, the more individuals there are in a confined space, the more complicated and delicate the hierarchy becomes. Aggression may become nearly constant, and can result in young and adult lower ranking individuals being chased, pinned, and having their fingers, finger tips, ear tips and tail tips chewed off. Groups in social housing should be monitored closely, especially when group members are removed for sale or research

Housing for invasive and infectious disease research

Monkeys on invasive, but not infectious, protocols are generally housed in biosafety level 1 (BSL-1) buildings. The humans they encounter are usually garbed in some sort of uniform: long-sleeve shirts, long pants, and tall boots for the care-techs; white lab coats and blue surgical scrubs for the research-techs, researchers, vet-techs and veterinarians. All of the humans wear surgical masks over their mouths and noses, one or more pairs of latex gloves on their hands, and eye protection (anything from safety glasses to full face shields).

Monkeys on infectious disease protocols will usually be kept in BSL-2 housing (BSL-3 and BSL-4 house increasingly infectious organisms (e.g. BSL-3 agents are transmissible by aerosol); precautions in these facilities correspondingly increase). Monkeys in BSL-2 and higher are generally single-caged. This area is usually more restricted and may feature a ‘dirty’ anteroom, footbaths in front of each animal room door, and can feature an air exchange system with positive air flow (dirty air is pushed out of the building) and HEPA (high-efficiency particle-arrestor) filters which ensure that clean air comes in (directional air-flow is not required). Humans working in these areas will often have to wear a jumpsuit (made of material that is often used to cover sheets of insulation in new houses, and feels like a waterproofed paper towel) over their uniform, a bouffant or surgical hair cover, double (or more) gloves, a thick face mask, and a full-face shield.

Cage cleaning

Cage cleaning is a loud, wet, and messy ordeal for humans and nonhumans alike. The technician methodically and systematically hoses excrement from the cages while the monkeys attempt to avoid the water by pushing themselves up into the corners of the cages (where they are still often unable to avoid getting wet). The waste pans are pulled out from under each cage, and their contents are loudly dumped on the floor. When all of the pans in a room are emptied onto the floor, the worker washes all of the waste toward a drain, where it is either collected (to become ‘hazardous waste’) or washed down the drain. In some labs, the pans are disinfected with chemicals daily. The tech rolls up the hose and moves on to the next room.

Cage washing requires ‘boxing out’ (moving into individual transfer boxes) perhaps half a room of monkeys all at once. The monkeys wait in the steel boxes while their empty rack is rolled out to the cage washer. The racks are rolled into the huge machine, where they will be washed (just like a dishwasher) and sanitized. After the walls and floor of the room have been sanitized, the rack comes back to the room and the monkeys are usually returned to their original configuration within it. Some monkeys may live in the same room for years, or for the duration of their lives, where they are unable to see anything beyond the door of the room.

Both cage cleaning and cage washing are incredibly loud and wet exercises, both of which can cause monkeys a great deal of observable stress and anxiety, as well as injury to workers. Monkeys are frequently killed when a tech fails to ensure that all of the monkeys are boxed out and the rack is sent through the cage washer with one or more residents inside.

A typical day in the life of a single-caged monkey

For caged monkeys, daily life in the laboratory generally includes five components: feeding, cleaning, cage washing, research procedures, and ‘enrichment.’ Sounds dull? It is.

Usually, the day will start with a quick visit from a veterinarian or vet-tech. The vet will check the animals’ conditions and will perhaps say a kind word. When the care-techs arrive, the monkeys may or may not get fed their breakfast of monkey chow right away. If the monkeys get their chow first thing, they are wise to hurry up and eat it before the hosing starts. If the cages are hosed before breakfast, the monkeys may have to wait several hours until the tech is free to feed them.

After feeding and cleaning, the rest of the day is often spent waiting and doing nothing (which can then lead to stereotypies (such as pacing or self-biting). Anxiety is ever-present: vets and vet-techs come and go (which can also be stressful for the monkeys, as these are not always people the monkeys look forward to seeing), roommates leave for veterinary or research procedures, return from procedures, or are fasted in anticipation of procedures. Knockdowns (sedation) and some procedures are done in the animal room (as opposed to the monkey being taken to a procedure room), which can cause observable anxiety to the subject’s neighbors. Care-techs bring or fill enrichment devices, may spend a moment visiting or grooming, and then start the arduous task of cage washing. The day ends with another meal: chow again, and maybe a piece of produce. Some facilities have enrichment technicians whose job it is to only provide enrichment to the animals. Unfortunately, there is often too much work for one person. For example, a facility may have only one enrichment technician for over 3,000 monkeys (living in various housing conditions) – this obviously does not leave sufficient time for the individual attention that singe-caged animals need.


[1] Hirschberg R, LaMontagne J, and Fauci A [2004]. Biomedical research – an integral component of national security. New England Journal of Medicine, 350:2119-2121.

[2] 9 CFR§ 3.80.

[3] Reinhardt V and Reinhardt A [2001]. Environmental enrichment for caged rhesus macaques. Animal Welfare Institute, Washington DC.

[4] 9 CFR § 3.81.