ILAR Journal Online, Volume 31(2) 1989: Perspectives on Animal Use

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ILAR Journal V31(2) 1989
Perspectives on Animal Use

Environmental Enrichment for Laboratory Animals
Bonnie V. Beaver

Dr. Beaver is professor in the Department of Small Animal Medicine and Surgery. College of Veterinary Medicine, Texas A&M University, College Station.

Introduction

Prior to the 1960s, many laboratory animals lived in "solitary confinement" in cages that were cramped, bare, and without stimulation. A typical environment might be described as follows: The cage walls are stainless steel bars because they are easy to wash. Floor space is often minimal. The closest conspecific is four feet away on days when no experiments occur. The view consists of four beige walls, fluorescent lights on a white ceiling, and an occasional sighting of another animal that shares the room. Although there is some variation--like solid walls instead of bars or clear plastic instead of stainless steel--the laboratory environment is rather barren.

Gradually, evidence began to accumulate that laboratory animals did not thrive in these environments and that experimental results were being compromised (Baer, 1971; Conalty, 1967). Researchers found that both the behavior of laboratory animals and research results can be influenced by space needs of animals, cage environments, lighting, noise, temperature, diets, schedules, social history, environmental control, and stocking density (Fox, 1986). The effects of animal caretaker styles on experimental results have also been discussed, because they can affect the behavior of animals (Fox, 1986). Even when animals' physical needs are met, psychological factors may exist and affect research outcomes.

Quality of life for animals in a laboratory setting has received some well-deserved attention, particularly after Congress amended the Animal Welfare Act in 1985 (P.L. 99-198) to require "a physical environment adequate to promote the psychological well-being of primates." Although this provision addresses the well-being of nonhuman primates, the scientific community is not limiting its focus to those animals or to the classical laboratory setting. Through environmental enrichment--that is, additions to an animal's environment with which it can interact--the scientific community hopes to improve the well-being of captive animals.

Specific environments can be evaluated on the basis of basic animal needs. Various cage arrangements and enrichment devices must be looked at from the animal's perspective. Whether or not an animal performs a particular behavior probably depends on several factors, including whether the behavior is typical for the species, how strong the motivation is, whether deterrents are present, and early learning experiences. Lorenz (1981) proposed that there is a specific drive for each major behavior pattern, and at some threshold, environmental stimuli will trigger the behavior. If the animal is prevented from expressing certain patterns or if the stimulus does not occur, the threshold will gradually decrease. Eventually the behavior could be expressed at an inappropriate time as a vacuum activity when no apparent external stimulus is present. Although reality may not be quite this simplistic, the hypothesis serves as a model for examining needs and explaining abnormal behaviors in laboratory animals.

Van Hooff (1985) modified a description of the response to a stimulus by defining it as reactive or spontaneous. For the stimulus that needs an immediate reaction, such as the appearance of a predator, the animal must give the situation the highest priority. The inability to respond to a reactive stimulus can result in behavioral changes. A caged animal in a laboratory or zoo that is unable to flee from or attack a person who is passing too close can be overstimulated to the point of distress. Spontaneous responses, as described by van Hooff (1985), are more dependent on a summation of stimuli. Such things as length of time since the last bout, amount of relief or excitement, strength of sensory input, and activities of others in a group can affect an animal's reaction. Ingestive behaviors provide several examples. Whether or not a cat will kill and eat a mouse depends on past experience catching mice, an acquired taste for a mouse, the length of time since its last successful hunt, and the amount of activity the mouse shows (Beaver, 1980).

Methods of Environmental Enrichment

Five basic methods can be used to alter an animal's environment. Experimental protocol and facility design will determine which ones are appropriate for a particular situation; however, ingenuity and a basic understanding of the behaviors of a species can provide almost endless possibilities.

Behavioral Enrichment

Behavioral enrichment is accomplished by creating an environment that mimics the wild habitat. It is often held to be the most desirable method of environmental enrichment, although a more natural environment can result in undesirable changes in behavior (Fox, 1986). In a laboratory setting, the introduction of predators to stimulate activity and the elimination of disease control could have devastating effects on resident animals and thus on experimental designs and results. Therefore, a modified wild environment is probably more appropriate. For certain primate colonies, this is accomplished by using large outdoor enclosures where animals can interact as if in a native social group (Figure 1). They can forage for insects and food on the ground, climb in branches and over protrusions, and choose their own mates.

Environmental enrichment in zoos may provide a model for laboratory animal facilities. Although the naturalistic settings are often appealing to human aesthetic values, they may not be interactive for the animals. Changes in the environment that promote instinctive or learned behaviors are more beneficial to the animal. This technique has been used in a number of zoo settings. Prey chasing has been simulated for servals (Felis serval) and Sumatran tigers (Panther tigris sumatrensis) by giving the large cats access to rapidly moving, artificial prey. Brachiation and leaping for food has been encouraged for whitehanded gibbons (Hylobates lar) by requiring that they obtain food by using rope "vines" to activate a feeder (Erwin and Deni, 1979; Markowitz, 1979, 1982; Schmidt and Markowitz, 1977).

Even the barest of laboratory environments can be enriched in a naturalistic way without compromising sanitation. Ropes can simulate vines for climbing and brachiating primates. Trees and branches allow climbing, swinging, and perching habitats for several species (Figure 2). When secured off the floor, they do not inhibit cleaning (Reinhardt, 1987). Straw, grass, or wood chip bedding, when appropriate to the laboratory's cleaning procedures, can be used to hide seeds, fruits, or other small foods. The raison board or scattered fruit can still be used to encourage foraging, if only for a short period of time (Moazed and Wolff, 1988). Straw on the floor or sterile soil in troughs encourages the natural tendency of pigs to root and decreases the aggressive interactions of pen mates (Wood-Gush and Beilharz, 1983).

Another variation of behavioral enrichment is based on the distribution of behavioral activity. If a wild animal spends 55 percent of a 24-hour period in some kind of activity and 45 percent resting and sleeping, the laboratory counterpart might be expected to show a similar pattern. Because time spent on food gathering is probably much less for the laboratory animal, other forms of activity might be encouraged in order to retain the 55:45 ratio.

Social Peers

The second method of environmental enrichment is the addition of social peers. A great deal of study has been done on restricted rearing conditions in primates. When infants were raised in isolation, they developed several abnormal behaviors, including body clasping, rocking, self-orientation, hyperaggression, rigid stances, sexual dysfunction, clinging, stereotypic circling, and self mutilation (Goldfoot, 1977; Harlow and Harlow, 1962; Harlow et al., 1966; O'Neill, 1988). When raised with artificial mothers made of cloth and wire or with members of their peer group only, the monkeys continued to develop abnormal behaviors, mutilated themselves under conditions of stress, and lacked reproductive and parenting skills as adults. The greater the amount of interaction of infants with conspecifics of all ages and the more complex the social interactions in which they participated, the more normal their behaviors were as adults (Goldfoot, 1977; Harlow and Harlow, 1962; Harlow et al., 1966). Introducing older animals to each other can be dangerous but occasionally has been successful (Erwin, 1985; Reinhardt et al., 1987).

Other studies have been conducted on the effects of restricted rearing conditions on dairy calves and rats. They indicated that a lack of early social contact can be detrimental to individuals of these social species as well (Broom and Leaver, 1978; Rosenzweig and Bennett, 1977).

Artificial Appliances

Although a wild-type environment for laboratory animals might be the most pleasing to humans, artificial appliances are an alternative. For example, a "jungle gym" constructed of polyvinyl chloride (PVC) pipe can substitute for a natural climbing object like a tree. Other objects encourage investigation and activity. A whole coconut can be rolled, thrown, rubbed, or dehaired. Bowling balls, hard nylon balls, sticks, large pails, milk crate swings, blocks, measuring scoops, infant teething toys, and toggle bolts encourage activity, especially among the young (Champoux et al., 1987; O'Neill, 1988; Renquist and Judge,'1985; Westergaard and Fragaszy, 1985). For primates that are restrained for long periods of time, finger puzzles or mobiles hold their attention and keep them busy (B. V. Beaver, unpublished observations).

Environmental enrichment by artificial appliances can also be used with nonprimate laboratory animals. Activity cages and running wheels work well with rodents. Dogs respond well to running through mazes. Activity can be encouraged for cats by hanging an object that can be swatted or watched (Figure 3) or by providing an object that will roll when batted. Gang housing also works well for cats especially if there are numerous perches on which individuals can rest. Scratching posts and large hollow tubes with several holes for cats to climb in and out can also be introduced.

Environmental enrichment using a variety of artificial objects has resulted in measurable increases in brain acetylcholinesterase, brain weight, cerebral cortical depth, and learning ability in laboratory rats. The density of brain neurons decreases (Diamond et al., 1964: Rosenzweig and Bennett, 1977). Increased learning ability has also been reported in other species that have enriched laboratory environments (Fox, 1971; Henderson, 1980).
Food Gathering Activities

Food gathering activities in the wild and in a laboratory animal facility are strikingly different. In the wild, an animal spends most of its time and energy searching for and gathering food. In a laboratory care facility, food is provided and is usually eaten quickly. Food quality in the laboratory is nutritious, but the animal is less active and weight gain must be carefully monitored.

Most environmental enrichment has focused on food-related behaviors of animals because of their strong motivation to accomplish a task when the result is food. In fact, once an animal has learned to work for its food, there is a strong tendency to continue to work for it even if another nonrestricted food source is readily available (LeBlanc, 1988; Markowitz, 1982). Mechanical and electromechanical devices from which animals earn their food have been installed in several zoos. Diana monkeys (Cercopithecus diana) at the Portland Zoo earned poker chips, which they could spend on food (Schmidt and Markowitz, 1977). A polar bear (Thalarctos maritimus) at the Washington Park Zoo vocalized into a microphone, after which fish were delivered into the pond for retrieval (Markowitz, 1982). Laboratory animal facilities are beginning to use these devices, particularly for nonhuman primates. A mechanical box has been used that delivers monkey chow after the animal pulls a rope (Figure 4) (LeBlanc, 1988). By placing the end of the rope some distance from the food dispenser, the animal must climb up the cage side to pull the rope and then climb down to retrieve the food. One olive baboon (Panio anubis) learned a way to grab the rope near the food box without having to climb. Others in the house soon mimicked her technique, and as a result, the rope placement had to be changed.

At another institution, food tubes were created by fitting one end of a pipe with a removable cap. The other end was attached to a board with other pipes so that the primates had access to the open end of several tubes (M. Bloomsmith, University of Texas Cancer Center, Veterinary Resources Division, Bastrop, Texas, personal communication, 1988). Chimpanzees (Pan troglodytes) have shown an interesting variety of techniques to get the food out of the tubes (Figure 5).

Control of the Environment

Lack of control over their environment is frequently mentioned as a stressor for laboratory animals (Line, 1987). Providing some means of control of nonfood items is the fifth method of environmental enrichment. Food is sometimes used in this method, but only to reward a specific behavior. Joffe et al. (1973) found that giving various degrees of environmental control to animals that were raised the same in all other ways resulted in interesting behavioral differences.

Classical studies on environmental control dealt with primate response to language. Signing, word boards, and computers were techniques by which animals indicated their wants, and humans usually provided the requested result (see general discussion by Goodall, 1986). Other studies allowed animals to have a more direct effect. For example, pigs were allowed to turn lights on and off (Baldwin and Meese, 1977), and primates were provided an on-off switch for a radio (Line et al., 1987). This concept of giving an animal more control over its environment is an interesting one that needs more investigation for various species.

Future Needs

To provide the best possible environment for various species of laboratory animals under different rearing and experimental conditions, much information on enrichment is still needed (Bernstein and Gordon, 1977; RoweIl, 1967). A flurry of activity--and some confusion--has been generated by the 1985 amendments to the Animal Welfare Act (P.L. 99-198). Much of the confusion is because the scientific community has not agreed on a definition of the term psychological well-being or whether environmental enrichment can be equated with psychological well-being. Add to the discussion the lack of a uniform understanding about the word stress, how to measure it, and its individual variation within a group. If scientists can agree on these issues, then appropriate methods to measure and assess psychological well-being in terms of the environment can be developed.

Written as a set of guidelines, the Guide for the Care and Use of Laboratory Animals (National Research Council, 1985) has become a standard for evaluating laboratory animal environments. However, many of the recommendations regarding cage size for various species are based on professional opinions and judgments rather than on comparative research data. Even when information on a species is published, comparisons are difficult because variables were different among protocols (Hite et al., 1977; Neamand et al., 1975; Rosenzweig and Bennett, 1977; Scott and Fuller, 1965; Thompson and Heron, 1954).

Line (1987), Fox (1986), and Dawkins (1983) distinguished between behavioral preferences and behavioral needs. Testing for animals' preferences for environments or foods may not ensure the physical health of the animals. For example, although fruit is an important component of primates' diet, their choosing it to the exclusion of other items jeopardizes their health. Because the desired object may only be available in limited supply in the animal's native environment, the species may not have evolved a mechanism to tell the body when it has had enough.

Reactions of animals to any type of environmental enrichment should be monitored to determine whether the desired outcome is achieved (Erwin, 1985). Various species will respond differently to the methods of enrichment. For example, hanging a rope in a baboon's cage--a species that does not brachiate, swing, or climb on vines--will probably get no response. The rope will be used, however, if offered to gibbons. Responses will also vary between age groups and between individuals raised under different social conditions. Social interactions may be desirable, but the severity of aggression between cage mates can be too great, particularly when pairings are forced rather than selected by the animals themselves.

The amount of time animals are active as compared to stationary is often used to monitor a program's success. Although some degree of activity for most animals is generally regarded as beneficial to health (Fox, 1986) and the lack of it is often useful for determining sickness (Markowitz, 1982), studies have not determined the amount of activity that is actually beneficial to any species or how closely the level of activity in captive animals should parallel that in the wild. Neither has it been shown that stereotypic behaviors (i.e., frequent, almost mechanical repetition of the same posture or behavior) are harmful or beneficial to the animal. Fox (1986) discussed the possibility that stereotypies help the individual maintain an optimal level of complexity in its life. They provide stimulation in a barren environment and help block out an environment that is too complex. Thus, the stereotypies may be an indicator of an unacceptable situation.

At least some stereotypies are associated with the release of neural endorphins (Brown et al., 1987; Dodman et al., 1987; Fox, 1986), which suggests that if the repetitions themselves are not harmful to the animal, these behaviors may not be bad. Additional study is needed for clarification.

Many techniques are available to enrich the environments of laboratory animals. Additional research is needed to determine the degree to which these methods are necessary or helpful to the animals involved.

References

Baer, H. 1971. Long-term isolation stress and its effects on drug response in rodents. Lab. Anita. Sci. 21:341-349.

Baldwin, B. A., and G. B. Meese. 1977. Sensory reinforcement and illumination preference in the domesticated pig. Anim. Behav. 25:407-507.

Beaver, B. V. 1980. Veterinary Aspects of Feline Behavior. St. Louis, Missouri: C. V. Mosby.

Bernstein, I. S., and T. C. Gordon. 1977. Behavioral research in breeding colonies of Old World monkeys. Lab. Anim. Sci. 27:532-540.

Broom, D. M., and J. D. Leaver. 1978. Effects of group-rearing or partial isolation on later social behaviour of calves. Anim. Behav. 26:1255-1263.

Brown, S. A., S. Crowell-Davis, T. Malcolm, and P. Edwards. 1987.Naloxone-responsive compulsive tail chasing in a dog. J. Am. Vet. Med. Assoc. 190:884-886.

Champoux, M., M. Hempel, and V. Reinhardt. 1987. Environmental enrichment with sticks for singly-caged adult rhesus monkeys. Lab. Primate Newsl. 26:5-7.

Conalty, M. L. 1967. Husbandry of Laboratory Animals. New York: Academic Press.

Dawkins, M. S. 1983. Battery hens name their price: Consumer demand theory and the measurement of ethological "needs." Anim. Behav. 31:1195-1205.

Diamond, M. C., D. Krech, and M. R. Rosenzweig. 1964. The effects of an enriched environment on the histology of the rat cerebral cortex. J. Comp. Neur. 123:111-120.

Dodman, N. H., L. Shuster, M. H. Court, and R. Dixon. 1987. Investigation into the use of narcotic antagonists in the treatment of a stereotypic behavior pattern (crib-biting in the horse). Am. J. Vet. Res. 48:311-319.

Erwin, J. 1985. Environments for captive propagation of primates: Interaction of social and physical factors. Pp. 299-305 in Primates: The Road to Self-Sustaining Populations, K. Benirschke, ed. New York: Springer-Verlag.

Erwin, J., and R. Deni. 1979. Strangers in a strange land: Abnormal behaviors or abnormal environments. Pp. 1-28 in Captivity and Behavior, J. Erwin, T. L. Maples, and G. Mitchell, eds. New York: Van Nostrand Reinhold.

Fox, M. W. 1971. Integrative Development of Brain and Behavior in the Dog. Chicago: University of Chicago Press.

Fox, M. W. 1986. Laboratory Animal Husbandry: Ethology, Welfare and Experimental Variables. Albany: State University of New York Press.

Goldfoot, D. A. 1977. Rearing conditions which support or inhibit later sexual potential of laboratory-born rhesus monkeys: Hypotheses and diagnostic behaviors. Lab. Anim. Sci. 27:548-556.

Goodall, J. 1986. The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Massachusetts: Belknap Press.

Harlow, H. F., and M. K. Harlow. 1962. Social deprivation in monkeys. Sci. Am. 207:136-146.

Harlow, H. F., W. D. Joslyn, M. G. Senko and A. Dopp. 1966. Behavioral aspects of reproduction in primates. J. Anim. Sci. 25: 49-67.

Henderson, N. D. 1980. Effects of early experience upon the behavior of animals: The second twenty-five years of research. Pp. 39-77 in Early Experiences and Early Behavior: Implications for Social Development, E. C. Simmel, ed. New York: Academic Press.

Hite, J., H. M. Hanson, N. R. Bohidar, P. A. Conti, and P. A. Mattis. 1977. Effect of cage size on patterns of activity and health of beagle dogs. Lab. Anim. Sci. 27:60-64.

Joffe, J. M., R. A. Rawson, and J. A. Mulick. 1973. Control of their environment reduces emotionality in rats. Science 180:1383-1384.

LeBlanc, S. A. 1988. Evaluation of a Behavioral Enrichment Program for Laboratory Baboons (Papio spp.). M.S. thesis, Texas A&M University, College Station.

Line, S. W. 1987. Environmental enrichment for laboratory primates. J. Am. Vet. Med. Assoc. 190:854-859.

Line, S. W., A. S. Clarke, G. Ellman, and H. Markowitz. 1987. Behavioral and hormonal responses of rhesus monkeys to an environmental enrichment apparatus. Am. Vet. Soc. Anim. Be-hay. Newsl. 10:6-7.

Lorenz, K. 1981. The Foundations of Ethology. New York: Springer-Verlag.

Markowitz, H. 1979. Environmental enrichment and behavioral engineering for captive primates. Pp. 217-238 in Captivity and Behavior, J. Erwin, T. L. Maple, G. Mitchell, eds. New York: Van Nostrand Reinhold.

Markowitz, H. 1982. Behavioral Enrichment in the Zoo. New York: Van Nostrand Reinhold.

Moazed, T. C., and A. V. Wolff. 1988. The raisin board as an environmental enrichment tool for laboratory primates. Lab. Primate Newsl. 27:16.

National Research Council. 1985. Guide for the Care and Use of Laboratory Animals. A report of the Institute of Laboratory Animal Resources Committee on Care and Use of Laboratory Animals. NIH pub. no. 86-23. Washington, D.C.: U.S. Department of Health and Human Services.

Neamand, J., W. T. Sweeny, A. A. Creamer, and P. A. Conti. 1975. Cage activity in the laboratory beagle: A preliminary study to evaluate a method of comparing cage size to physical activity. Lab. Anita. Sci. 25:180--183.

O'Neill, P. 1988. Developing effective social and environment enrichment strategies for macaques in captive groups. Lab. Anim. 17:23-36.

Reinhardt, V. 1987. Improved installation method for branches as cage enrichment. Lab. Primate Newsl. 26:1.

Reinhardt, V., D. Cowley, S. Eisele, R. Vertein, and D. Houser. 1987. Preliminary comments on pairing unfamiliar adult female rhesus monkeys for the purpose of environmental enrichment. Lab. Primate Newsl. 26:5-8.

Renquist, D. M., and F. J. Judge. 1985. Use of nylon balls as behavioral modifier for caged primates. Lab. Primate Newsl. 24:4.

Rosenzweig, M. R., and E. L. Bennett. 1977. Effects of environmental enrichment or impoverishment on learning and on brain values in rodents. Pp. 163-196 in Genetics, Environment, and Intelligence, A. Oliveerio, ed. New York: Elsevier.

RoweIl, T. E. 1967. A quantitative comparison of the behavior of a wild and caged baboon group. Anita. Behav. 15:499-509.

Schmidt, M. J., and H. Markowitz. 1977. Behavioral engineering as an aid in the maintenance of healthy zoo animals. J. Am. Vet. Med. Assoc. 171:966-969.

Scott, J. P., and J. L. Fuller. 1965. Dog Behavior: The Genetic Basis. Chicago: University of Chicago Press.

Thompson, W. R., and W. Heron. 1954. Exploratory behavior in normal and restricted dogs. J. Comp. Phys. Psych. 47:77-82.

van Hooff, J. A. R. A. M. 1985. Behavior requirements for self-sustaining primate populations--some theoretical considerations and a closer look at social behavior. Pp. 307-319 in Primates: The Road to Self-Sustaining Populations, K. Benirschke, ed. New York: Springer-Verlag.

Westergaard, G. C., and D. M. Fragaszy. 1985. Effects of manipulatable objects on the activity of captive capuchin monkeys (Cebus apella). Zoo Biol. 4:317-327.

Wood-Gush, D. G. M., and R. G. Beilharz. 1983. The enrichment of a bare environment for animals in confined conditions. Appl. Anim. Ethol. 10:209-217.

Figure 1 A large natural enclosure for primates encourages activity and social interactions Photo courtesy M. Bloomsmith.

Figure 2 Tree branches provide a varied environment for exploration and activity by primates. Photo courtesy of M. Bloomsmith.

Figure 3 Allowing these research cats to watch fish swimming reduced the amount of psychogenic grooming.

Figure 4 The baboon must climb the cage bars and pull a rope in order for food to be delivered into a box attached to the cage.

Figure 5 A chimpanzee uses a stick to reach food in tubes that are attached to the cage wall. Photo courtesy M. Bloomsmith.

Comentary
Evalyn F. Segal

Dr. Segal is professor emerita of animal learning and behavior in the Department of Psychology, San Diego State University, California. She served for three years on the Committee on Animal Research and Ethics of the American Psychological Association (APA) and has chaired several APA symposia on animal research ethics.

Dr. Beaver's article reminds us that although the 1985 amendments to the Animal Welfare Act (P.L. 99-198) raised the issue of psychological well-being in reference to captive primates, there is no reason not to extend the same concerns to other laboratory species. It is true that the scientific community has not reached (and may be a very long time in reaching) consensus on what psychological well-being means. Nevertheless, by inserting this expression into the debate on laboratory animal welfare, Congress made the point that laboratory animals have needs beyond physical health, nutrition, sanitation, and the like. Vital as these veterinary concerns are, psychological concerns are just as important.

As a comparative psychologist, I have no difficulty agreeing with Dr. Beaver, a veterinarian, on a pragmatic interpretation of psychological well-being: behavior is the issue. Idleness, monotony, and solitude are pathological conditions for most, if not all, mammalian species; they engender both behavioral/cognitive and physiological/immunological aberrations and render captive animals unfit subjects for either psychological or biomedical research. For scientific as well as humane reasons, we need to design laboratory environments that permit the expression of animals' behavioral and cognitive capacities.

Behavioral researchers from experimental psychology and ethology need to join forces with veterinarians and biomedical researchers to design optimal laboratory environments. With a little ingenuity and interdisciplinary cooperation, we surely can design multipurpose maintenance-and-research environments that all at the same time (1) permit animals to express some part of their natural behavioral repertoire, (2) enable us to explore their cognitive capacities, and (3) make the animals available for long-term physiological studies. For example, we can combine ethological and psychological knowledge to design foraging tasks that in some respects simulate natural foraging (thus permitting the expression of species-typical behavior), but in other respects challenge the animals in cognitively more demanding ways than nature may do. To avoid the ill effects of idleness, foraging tasks could borrow a trick from the behavior analyst's laboratory: a judicious choice of food reinforcement schedules will keep animals engaged in vigorous, motivated activity for long periods--the animal would get adequate food, gainful employment, cognitive challenge, physical exercise, and the exercise of its natural foraging talents, all at once.

I recently had the privilege of editing a book (Segal, in press) containing 26 chapters of expert advice on behavioral and environmental enrichment for captive primates ranging from the prosimians to the great apes. The knowledgeable primatologists and psychologists who contributed their wisdom and experience to the book taught me how much can be done, and is being done at selected primate facilities, to enrich the environments and challenge the behavioral capacities of laboratory animals. Two themes appear again and again in the book: one I have already discussed here is animals' need for "gainful employment." The other theme is the need for conspecific companionship for species as intrinsically social as primates. Several authors independently made the point that the single most important thing one can do to enrich the life of a captive primate is to provide it with a companion animal. Dr. Beaver mentions research on other social species--dairy calves and rats--and shows that they, too, thrive best in social groups.

Companionship and activities that engage and challenge behavioral capacities; these, I believe, are what the future holds for laboratory animals. Science will gain by way of healthier subjects, more reliable data, and new and surprising knowledge. The price we have to pay is giving up simplistic notions about the husbandry requirements of laboratory animals. Some day we will look back and wonder how we could ever have thought otherwise.

References

Segal, E., ed. In press. The Housing, Management, and Psychological Well-being of Captive Primates. Park Ridge, New Jersey: Noyes.

Comentary
Joseph S.Spinelli

Dr. Spinelli is director, Animal Care and Cell Culture Facility, University of California, San Francisco.

Dr. Beaver's article is an important reminder that the whole area of environmental enrichment for animals and their psychological well-being may be one of the most important areas of study in laboratory animal science over the next few years. Perhaps her most important comments are the final two sentences of the article: "Many techniques are available to enrich the environments of laboratory animals. Additional research is needed to determine the degree to which these methods are necessary or helpful to the animals involved." These sentences recognize that a variety of techniques will be useful and that a great deal of research is necessary in this area. Indeed, this study by laboratory animal scientists and their colleagues in other disciplines regarding the psychological well-being of laboratory animals and how to enrich their environments is in its infancy. Just as those who work in the field of laboratory animal science have done an outstanding job of characterizing and preventing physical disease in laboratory animals, we must now move forward in characterizing those factors that promote psychological health in laboratory animals. As with physical diseases, this will require well-documented scientific investigation. Such investigations, which will stand the scrutiny of peer review, should be enthusiastically published in journals commonly read by those who work in the field of laboratory animal science.

In the article, Dr. Beaver gave her definition of environmental enrichment. Because there is no universal agreement regarding a definition for environmental enrichment, all authors should do the same until a formalized definition is agreed to by those working in the field. Although 1 commend her for including a definition of environmental enrichment, I have some problem with the definition she used. I do not believe all additions to an animal's environment with which it can interact constitute environmental enrichment. Some additions to an animal's environment with which it might interact could be harmful. That would hardly be enriching. By building on her definition, perhaps one could define environmental enrichment as "additions to an animal's environment with which the animal voluntarily interacts and, as a result, experiences improved physical and/or psychological health."

I am happy that Dr. Beaver calls readers' attention to five basic methods of environmental enrichment. Some will be tempted to argue whether there are five or more or less. To do so misses the major point. Although various groups have favorite types of environmental enrichment that they vigorously proselytize, in fact there are a variety of strategies that will be useful singly or in combination to promote the psychological well-being of laboratory animals.

Although interaction with conspecifics is important, many believe that pleasant interaction with humans is also beneficial for many species. Hand feeding, grooming, talking, and stroking of animals by humans may be an important source of environmental enrichment. This concept should be studied further.