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Figure 16 A hanging piece of wood receives much attention by a caged rat. (Photo by E. Orok-Edem; reproduced from Animal Technology 1994, Vol. 45, No. 1 with permission of the ATW Editorial Board) |
3.2. Environmental Enrichment
Environmental Enrichment is the provision of stimuli that promote the expression of species-appropriate behavioral and mental activities in an understimulating environment (Reinhardt and Reinhardt, 2002). Some species-typical behaviors, such as injurious aggression, are inappropriate within the context of confinement and are, therefore, excluded from this definition.
In the wild, rodents shun open areas, because they offer no visual protection from potential predators. In captivity, they will not use the space of an enclosure containing no structures evenly, but will shy away from the center and spend most of their time at the periphery (Fredericson, 1953; Ross et al., 1966; White et al., 1989; Anzaldo et al., 1994), moving and resting close to the surrounding walls (thigmotaxis). The central, unprotected area of such an enclosure is functionally of little use to the animals.
Anzaldo et al. (1995) compared the preference of male Sprague-Dawley rats kept in groups of six for a barren standard cage versus a 50 percent smaller cage that was structured with two L-shaped partitions, subdividing the cage into a rectangular corridor with two entrances. These structures provided the rats with additional wall contact and a relatively small wall-encircled central area in which they could huddle and sleep together. During a 24-hour videorecording the animals spent:
When the rats could choose between the small cage with the L-shaped partitions and another cage of the same size but furnished with two elevated platforms of unspecified height, they again preferred the cage with the increased wall contact options (Anzaldo et al., 1994). Wall contact is probably essential to the rats' sense of security, and hence is more important for them than platforms or additional empty space.
Chmiel and Noonan (1996) gave singly caged Long-Evans rats the choice of staying in either half of a partitioned double-cage, one side of which was barren and the other furnished with one of several potentially enriching objects. The animals showed a significant preference for the furnished cage section when it was provisioned with a small birch ball (4.5 cm diameter), a small gnawing block (2.5 x 2.5 x 2.5 cm) drilled with two holes, or a golf ball (4.5 cm diameter). The rats chewed all three objects into small bits over the course of four days. The small birch ball was the most attractive object. The rats showed no special interest in the furnished section of the cage when it contained a larger birch ball (7.6 cm diameter), a larger wood block (9 x 9 x 2 cm), a Y-shaped PVC section (6 cm diameter), a large or a small tin can (10.4 cm or 7.7 cm diameter), a small acrylic ball (2.5 cm diameter), a small acrylic block (1.6 x 1.6 x 1.6 cm), or a bone-shaped rawhide (7 cm long). These items had no enrichment value for them.
Eskola et al. (1999) videotaped groups of four Wistar rats who were each provisioned with one 6 x 6 x 6-cm aspen block with penetrating drilled holes (diameter of 1.9 cm) on each side and one 20 x 12 x 12-cm aspen box. The two objects were replaced once a week. Throughout a test period of five weeks both items were consistently used for gnawing, as measured in the reduction of wood volume. During the day, the rats spent about three percent of the time in contact with the block, 87 percent of the time in the box, and two percent of the time on top of the box. During the night, they spent 11 percent of the time in contact with the block, only 24 percent in the box, but 34 percent on top of the box. This activity pattern reflects the animals' nocturnal life style, with the dark shelter serving as a refuge and place to sleep during the day, and as an orientation platform during the night.
When given a choice between the large perforated aspen block and a much smaller (1 x 1 x 5 cm) non-perforated aspen block, the rats contacted the large one about seven percent of the time, and the small one less than one percent of the time (Mering, 2000).
Aspen wood is safe for the animals. Robertson (1999) exposed 20 Sprague-Dawley rats to 13.5 x 4 x 4-cm aspen sticks over a three-week period. The animals gnawed the wood but no signs of gastrointestinal tract injuries were found, suggesting that the material was safe.
Orok-Edem and Key (1994) tested two enrichment objects in groups of five Lewis rats. Each group was exposed for a period of five days to (a) one approximately 16 x 2 x 0.2-cm tongue depressor made of birch wood, and (b) one 3-cm-long broom handle section hanging on a stainless steel clip from the top of the cage (Figure 16). Both objects triggered the primary behavior of gnawing. The suspended piece of wood received significantly more attention than the loose piece of wood, probably because it had the dynamic element of swinging back and forth when contacted. Nonetheless, the tongue depressor had to be replaced every day, because the rats shredded the material into tiny pieces within 24 hours. The suspended broom handle section remained in the cage throughout the test period, but there was hardly any wood left by the end of the study.
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Figure 16 A hanging piece of wood receives much attention by a caged rat. (Photo by E. Orok-Edem; reproduced from Animal Technology 1994, Vol. 45, No. 1 with permission of the ATW Editorial Board) |
Patterson-Kane et al. (2001) gave singly caged Hooded Norway rats the choice of spending time in a barren cage versus an equally-sized cage furnished with either a PVC tube (8-cm diameter), a wooden platform (unspecified height), two gnawing sticks (~ 1-cm diameter), a plastic cylinder (15-cm diameter), or three tunnels glued together in a pyramid. The rats had a significant preference only for the cage with a platform (Figure 17). They had no apparent interest in the other objects. Nelson et al. (2003) videotaped singly caged Wistar rats in a test cage with two platforms of unspecified material that were placed at different unspecified heights. Individuals spent an average of 21 percent of one 24-hour recording session on the platforms. This could reflect the novelty effect of the platforms, because they were not the habitual furniture of the rats' home cages.
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Collier et al. (1990) noted that singly caged Sprague-Dawley rats spent about seven percent of the 24-hour day in a freely accessible running wheel to which the animals had been habituated for ten days. They readily worked by pressing a bar to obtain access to the wheel, indicating that wheel running was a rewarding experience for them.
Coviello-McLaughlin and Starr (1997) examined the effect of environmental enrichment in the form of nestlets and cardboard tubes on post-surgical premature wound clip removal by BALB/c nude mice. The percentage of animals removing wound clips dropped from:
Hobbs et al. (1997) furnished the group-cages of four male CD-1, DBA/2 and B6CBF1 mice with two halves of a 10-cm-long plastic tube, a marble with a 1.3-cm diameter, and a nestlet. Six-hour videotape recordings during the night revealed that all three strains spent significantly more time contacting the nestlets (75 percent) than the tube (14 percent) and the marble (one percent).
Mice climb on and explore tubes, but there is no scientific report demonstrating their long-term usefulness as burrows or sleeping sites (Figure 18a & b).
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| Figures 18a&b Mice explore ceramic or plastic tubes, but there is no scientific report demonstrating their long-term usefulness as burrows or sleeping sites. (Photos by Maureen Hargaden, Hoffmann-La Roche Inc., Nutley, NJ, USA. ©Roche Laboratories Inc., 2005) | |
Sherwin (2004a) tested C57BL/6 mice individually in a preference cage with a mirror placed in one of the two interconnected cage sections. The animals showed no preference for the section with the mirror, but 13 of 16 mice spent less time in the cage section with the mirror than in the section without the mirror. Food consumption from the feeder immediately adjacent to the mirror was significantly lower than from the feeder in the other cage section. This indicates that the mirror had aversive qualities and was not a species-appropriate environmental enrichment object.
Sherwin and Nicol (1996) and Sherwin (1998) demonstrated in a series of experiments that TO mice are highly motivated to gain access to a metal rung-type running wheel with a 15-cm diameter. Harri et al. (1999) found that single C57BL/6 mice with free access to such a wheel spent approximately eight percent of the 24-hour day running (Figure 19).
Banjanin and Mrosovsky (2000) gave C57BL/6 mice the choice of using different types of running wheels. The animals showed a strong preference for a standard wheel that had a black plastic mesh (3.5 x 3.5 mm) wrapped around the outside of the rods.
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Figure 19 Running wheels provide very attractive cage enrichment for mice. (Photo by Maureen Hargaden, Hoffmann-La Roche Inc., Nutley, NJ, USA. ©Roche Laboratories Inc., 2005) |
Arnold and Westbrook (1997/98) placed a T-shaped PVC pipe (8-cm diameter) or a pint-sized clear glass jar (12.7-cm diameter) into the cages of groups of four same-sex golden hamsters. After being exposed to each of these two objects for two weeks, the hamsters contacted the jar more than twice as often as the pipe. The jar was primarily used for standing on top of it while peering out from the cage.
Hamsters are attracted to running wheels, spending much of their time exercising in them (Richards, 1966; Mrosovsky et al., 1998). Gebhart-Henrich et al. (2005) compared the behavior of female hamsters who had access to a functional or a non-functional large running wheel. Hamsters with a functional wheel showed significantly less stereotypical bar-mouthing than hamsters with non-functional wheels.
Reebs and St-Onge (2005) found that the animals have a strong preference for wheels that are larger than those often used for rats (35 cm vs. 23 cm diameter) and for completely circular wheels over truncated ones (Figure 20).
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There are no data-supported published reports on environmental enrichment options for gerbils. Like other small rodents, gerbils spontaneously make use of running wheels (Roper, 1976).
Environmental enrichment options for guinea pigs have been described but their usefulness has not been tested and documented in the literature. Scharmann (1991) demonstrated with a photo that guinea pigs use gnawing sticks of unspecified dimensions.
Whary et al. (1993) provisioned the floor pen of eight female NZW rabbits with a 30 x 150-cm shelf mounted 25 cm off the floor, a 60 x 20-cm container filled with absorbent chips, and a 75-cm-long PVC tube (30-cm diameter) anchored to the floor in the center of the pen. Over a five-week period, the rabbits were seen near or in the litterbox 42 percent of the time, near or in the tube 45 percent, on the resting board ten percent and under the resting board three percent of the time. The litterbox was preferentially used as a resting area and for playfully hopping in and out of the box in rapid succession. The PVC tube was very popular as a retreat and as an object of investigation. Individuals often rested in the tube for several minutes before being "gently" displaced by another rabbit entering the tube from behind. The tube was rarely empty. The surface of the shelf was used only occasionally for resting. The area under it served mainly as refuge during alarming situations (Figure 21).
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Figure 21 Rabbits use platforms primarily as a place of refuge during alarming situations. (Photo by Tamara Godbey, University of British Columbia, Vancouver, Canada) |
Huls et al. (1991) placed one 23 cm long gnawing stick fastened to the side of the cage, one wooden parrot toy suspended from the top of the cage, and one brass wire cat toy in random order over a period of five days into the cages of eight NZW does and collected behavioral data, for each object during five 5-minute observations, at 15-second intervals. The rabbits chewed the stick and nudged it with their heads during 94 percent of observation intervals, the wooden toy during 77 percent and the brass toy during 79 percent of observation intervals. The long-term attractiveness of these three objects was not examined.
Wood items seem to be safe for rabbits. Brooks et al. (1993) noted no clinical problems in 48 animals who had access to regularly replaced fir sticks (12 cm long, 2.5 cm in diameter) throughout a two-year test period.
Johnson et al. (2003) tested a stainless steel rattle in singly caged NZW rabbits. The toy was contacted frequently in the beginning, but both females and males quickly lost interest and virtually ignored it after eight weeks. Harris et al. (2001) exposed singly caged NZW rabbits to three toys and videotaped the animals daily for one hour during a 15-day test period. The 10-cm-diameter polyethylene ball containing a stainless-steel jingle and the 11 cm long rubber toy generated much interest in the beginning, but by day six neither toy generated more than one minute of interaction both by females and males. The animals never paid much attention to the 10-cm-diameter nylon ball (Figure 22).
Enrichment objects made from plastic material can carry a certain risk. Shomer et al. (2001) reported an injury caused by a perforated hollow ball made of hard plastic. The ball had been considered safe, because it was made of non-toxic material, had no sharp edges, was too large to be swallowed or inhaled, and was judged too sturdy to be broken. However, the ball became lodged in the incisors of a doe, preventing her from eating or drinking, and causing trauma to her gums.
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Edgar (2004) attached a mirror to the inside of the cages of singly housed NZW rabbits and videotaped the individual subjects' behavior and location in the cage during a 7-day test period. No evidence was found that either does or bucks were attracted by the mirrors, even though their responses suggested that the animals did perceive the image in the mirror as a social counterpart. Jones and Phillips (2005) recorded the behavior of singly caged Dwarf Lop and Lionhead does after mirrors were installed at the rear and both side walls of their living quarters. The rabbits spent an average of about 63 percent of the first hour sniffing and scrabbling at the mirrors versus about eight percent of the time on day seven. This indicates that the novelty effect of the mirrors was of short duration.
Patterson-Kane (2002) tested female and male Wistar rats in a T-maze preference apparatus and found that all subjects showed a significant preference [66%] for a large [1620 cm2 ], yet barren, cage over a small [540 cm2 ] barren cage. The preference was comparable to that shown by rats for a nest box versus an empty cage (Patterson-Kane et al., 2001). Using the same paradigm, Patterson-Kane (2001) failed to detect, either in female or in male Hooded Norway rats, a significant preference for a large, empty cage [1800 cm2 ] over a small empty cage [900 cm2 ]. The animals were not inclined to work to get access to a barren cage that was twice as large as their home cage (Patterson-Kane et al., 2002).
Galef & Durlach (1993) gave male Long-Evans and Sprague-Dawley rats the choice to enter 1240-cm2 barren cages that were 16.8 cm or 23 cm high. The rats exhibited no preference for either of the two cages.
Von Weiss & Taylor (1985) examined the issue of preferred cage height more systematically in male Wistar rats. The subjects had simultaneous access to barren standard cages [840-cm2 ] that were either lower or higher than the legally required 15 cm. The rats showed a statistically significant preference for the 18-cm-high cage. The percentage of a 48-hour test period spent in the four cages was:
Sherwin and Nicol (1997) trained male TO mice to operate a switch to move from a 270-cm2 barren cage to another barren test cage that was either smaller (196 cm2), moderately (360 cm2 and 625 cm2), or substantially larger (1600 cm2 ). The animals readily worked to gain access to the test cages probably out of curiosity but failed to show a preference for a larger vs. smaller cage. The similarity in responses is noteworthy, since the smallest cage provided less space than the standard cage just enough space for the mouse to turn around while the largest cage offered several times more space than the standard cage. Sherwin (2004b) repeated this study with group-housed female CB57 mice using correspondingly-sized cages and obtained equivalent results: The mice did not differentiate between small and large barren cages in their motivation to get access to them, probably because none of the cages offered structured space to be explored and functionally used.
Mahon et al. (2005) determined that breeding trios of C57BL/6 mice had a higher birth rate (9.6 pups/female) in presumably unfurnished, larger than normal 20 x 43 cm cages than in standard 15 x 25 cm cages (7.2 pups/female). Keeping the mice in larger cages not only improved their breeding performance but it also decreased labor investment.
Krohn et al. (1999) compared the activity and behavioral expressions of individually housed female Ssc:CPH rabbits kept in barren cages that were 2800 cm2 or 5600 cm2 and found no significant differences.
Rodents and rabbits are biologically adapted to spend a great portion of their time searching for and processing food. Neuringer (1969) and Carder and Berkowitz (1970) showed in rats that this inherent foraging drive is so strong that the animals readily work (press a lever) for food even if identical food is freely available to them. This behavioral response is so conspicuous that it has received a special technical term, "contrafreeloading" (Inglis et al., 1997).
Wrightson and Dickson (1999) redesigned the traditional food hopper for group-housed rats of unspecified strain by covering the access area with a sheet of aluminum, leaving only a narrow slot open. Rather than rapidly collecting and eating their pellet ration, the rats now had to skillfully retrieve their food, thereby engaging in a more natural foraging-like behavior. After eight months of exposure to such a limited-access hopper, the rats were still slim (prevention of obesity!) and showed no adverse clinical effects. Since up to three rats could obtain food at the same time, the new hopper did not lead to antagonism resulting from competition. Johnson et al. (2004) promoted more foraging activities in pair-housed Wistar rats by placing their daily pellet ration in a 3-cm raised metal dish and then covering the food with gravel. This simple modification of food presentation increased significantly the time that the rats spent obtaining their food.
There are no published articles addressing feeding enrichment possibilities for mice, hamsters and gerbils.
Sutherland and Festing (1987) concluded from casual observations that guinea pigs need hay, and that outbreaks of pathological hair-pulling and -chewing may occur when hay is not provided. Guinea pigs seem to indicate the great pleasure they derive from burrowing and foraging in hay by vocalizing when attending personnel are about to replenish it (Figure 23).
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Figure 23 Old rabbit cages can be recycled for group-housed guinea pigs. The Macrolon IV cage provides an area of solid flooring with a bedding of sawdust and daily hay. The guinea pigs defecate and urinate primarily on the grid floor of the rabbit cage, but they spend most of the time in the Macrolon cage nibbling and eating hay, sleeping in hay and hiding in "dens" made of hay. (Photo by Richard Weilenmann, Hoffmann-La Roche Ltd., Basel, Switzerland) |
Metz (1987) gave groups of five NZW rabbits continual access to straw over a period of four weeks. The animals spent an average of 11 percent of the 24-hour day exploring, nibbling and eating straw. Lehmann (1990) mounted a rack of hay in the pen of ten NZW rabbits and replenished it daily. Individuals spent eight percent of the time retrieving and eating hay (Figure 24). Engagement with hay was highest at dawn and dusk. Berthelsen and Hansen (1999) distributed hay on the cage tops of singly housed NZW x French Lop rabbits. The animals retrieved and ate hay 16 percent of the time during the day and nine percent of the time during the night.
Lidfors (1997) provisioned singly caged NZW rabbits daily with (a) either 20 g of hay stuffed into a plastic bottle so that the subjects had to manipulate the material to retrieve it, or (b) two aspen sticks of unspecified dimensions. Over a four-week observation period, hay was contacted 11 times more often than the sticks.
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Figure 24 Offering hay and vegetables in a hay rack, rather than distributing it directly onto the floor, promotes food retrieval and food processing behaviors in rabbits. (Photo by Novo Nordisk A/S, Denmark) |
3.2.4. Interaction with Humans
Werner and Latané (1974) and Werner and Anderson (1976) noticed that male and female Sprague-Dawley rats readily get attracted to the human hand that interacts with them in rat fashion by poking, lifting, rubbing and scratching, tapping, and tumbling but, of course, never holding them. Davis and Pérusse (1988) confirmed in female and male Wistar rats, that about half of the subjects tested worked in a Skinner box for petting by and social interaction with a familiar human in the absence of any other reward. Positive interaction with humans can, therefore, serve as species-appropriate environmental enrichment for these rodents.
Hirsjärvi and Junnila (1988) and Hirsjärvi and Valiaho (1995) exposed adult male Wistar rats, who had been either (a) gently handled on a regular basis or (b) left with the routine care involving minimal handling, to the presence of a potential predator the experimenter standing next to an open test arena. The gentled rats showed lower frequencies and durations of freezing and significantly lower incidences of loose stool and rigid movements than the nongentled rats, suggesting that the regular gentle handling had reduced their fear towards the experimenter (Figure 25).
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Shyu et al. (1987) compared the pharmacokinetics of two different drugs (amikacin and ticarcillin) injected in Sprague-Dawley rats who were either (a) handled daily prior to the study and then held rather than wrapped in a towel and petted by the investigator during the experimental procedure or (b) were not extra handled but simply picked up and wrapped in a towel while the experimenter obtained a tail vein blood sample. For rats, who were handled in a manner to minimize stress, pharmacokinetic profiles of the two drugs were typical. Aberrant serum concentration-time curves were observed in rats who received no extra gentle handling.
Nerem et al. (1980) tried to alleviate the potential stress associated with single-caging in male NZW rabbits. The animals were assigned to an atherosclerosis study. One group of animals received normal laboratory animal care while the other group received special attention by one person who talked to, played with and stroked each subject daily during brief visits (Figure 26). The rabbits with human contact were significantly less susceptible to atherogenesis as measured in aortic sudanophilia than control rabbits. The study was repeated and the result confirmed with a different set of rabbits.
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| Figure 26 The affectionate relationship of attending care personnel with the animals in their charge is a safeguard not only that the animals receive optimal care but also that they are not unduly disturbed by the presence of people during scientific experiments. (Photo by Natasha Down, York University, Toronto, Canada) |
New things elicit curiosity and if they are not dangerous, exploration. Beyond this novelty effect, however, many objects quickly lose their attraction, and hence have no true environmental enrichment value for the confined animal. It is sometimes recommended to rotate toys in order to recharge their novelty effect. This strategy may not be practicable in facilities that keep thousands of animals for research purposes. Rather than investing the extra time needed to exchange the toys on a regular basis, it would probably be more effective and less expensive to offer the animals enrichment in which they do not lose interest over time.
Toys do have their value under the condition that their long-term effectiveness as enrichment gadgets has been tested and documented for the species they are designed for.
Properly-sized wooden objects prompt rats to engage in species-typical gnawing and manipulating without causing noticeable clinical risks. Along with the natural dehydration process of the wood, these behaviors make the object constantly change its configuration, size and texture. The gnawing block or gnawing stick thereby becomes a dynamic object which, unlike indestructible objects, maintains its novelty effect until it is completely worn down. Rats don't seem to get bored by wooden material but by plastic or other relatively indestructible objects. They should, therefore, always have access to gadgets made of natural wood to help them cope with boredom.
Objects that can be turned into nesting material seem to be the preferred environmental enrichment for mice.
With the exception of guinea pigs, rodents make use of running wheels with consistency. They should, therefore, be provisioned with appropriate running wheels to allow them to engage in some exercise.
Vertical structures offering additional wall contact and elevated look-out posts provide particularly suitable environmental enrichment for rats.
PVC tubes are very useful enrichment objects for rabbits. Instead of commercial toys in which the animals quickly lose interest, each rabbit enclosure should be furnished with one or several PVC tubes as objects for investigation and places for retreat.
Space has little or no enrichment value unless it is structured. Confined rats, mice and rabbits make no clear distinction between a barren cage that is small and one that is large and has the same shape. This does not imply that they would not benefit from cages larger than the minimum-size; the additional space of larger cages should serve to hold appropriate environmental objects and structures that promote species-typical behaviors.
Since rodents shun open areas, the determination of their minimum floor space requirements will also have to take the shape of the cage into consideration. If a cage is not furnished with a shelter, the cage should be relatively long and narrow. This will minimize the area of the central open field that is avoided by the animals.
Systematic preference studies are required to objectively determine the most species-adequate shape of the primary enclosure and the minimum horizontal and vertical unstructured space requirements of rodents and rabbits. The pilot study by von Weiss and Taylor (1985) demonstrates for male Wistar rats that the animals have a strong preference for a cage that is moderately (3 cm) but not substantially (7 cm) higher than the legal requirement of 15 cm. The legal determination of minimum horizontal space is particularly important for caged rabbits (Figure 27a & b). These animals are prone to develop muscular atrophies, poor bone growth and backbone distortions as a result of lack of locomotor activity in small cages (Wieser, 1984; Bigler and Lehmann, 1991; Rothfritz et al., 1992) that may provide the rabbit the legally required floor space to make normal postural adjustments (United States Department of Agriculture, 2002) but is not large enough to allow for the rabbit-typical hopping.
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| Figures 27a&b The dimensions of the primary enclosure have to take species-typical postures into account to provide reasonably comfortable living quarters. For an adult, 4-6 kg NZW rabbit the enclosure should be no less than 80 cm long to allow for resting in the rabbit-typical lateral sternal position (a), and 75 cm high for sitting in the rabbit-typical lookout position (b; Gunn-Dore, 1997). |
Modifying the food hopper so that skillful manipulations are required to obtain the standard food ration is a simple, practical and effective enrichment technique allowing rats, and probably also mice, hamsters and gerbils, to get more actively involved in the feeding process. The idea of having the animals work for their daily food ratio, and thus engage in foraging behavior by modifying their food boxes, has been applied with success also in nonhuman primates (Reinhardt, 1993; Murchison, 1994). It is probably the least expensive, yet most effective feeding enrichment option.
Guinea pigs and rabbits are easily prompted to engage in foraging behavior by offering them hay on a daily basis.
There is a need to study the impact of regular positive interaction with humans, and to implement the findings in the daily work schedule of attending care personnel and animal technicians. The few articles dealing with this issue in rats and rabbits strongly suggest that the confined animal subject receives special benefits from such interaction not only in terms of distraction in an otherwise boring environment but also in terms of stress reduction and decreased fear of humans.
Developing a relationship with rodents and rabbits that is based on trust rather than fear will also provide the condition for positive reinforcement training, an area that is being explored intensively with great success in nonhuman primates assigned to biomedical research (Reinhardt, 1997), but that has been largely ignored by researchers working with rodents and rabbits.
Inertia of tradition is a big hindrance for concerned animal care personnel, veterinarians, and young scientists who wish to change the status quo of rodents and rabbits assigned for biomedical research. The outlook for animals kept in European facilities is more promising than for those kept in the United States. While European animal welfare law (European Economic Community, 1986) covers all rodents, including those who make up the bulk of laboratory animals, i.e., rats and mice,
US "animal" welfare law and its regulations explicitly exclude without any stated reason these animals in its definition of the term animal (Animal Welfare Act, 2002; United States Department of Agriculture, 2002).
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This lack of protection makes the situation for rats and mice particularly problematic in the United States, because there is no serious legal incentive to take the welfare of these "non-animals" into earnest consideration as we design their living quarters and define the ways they are handled during procedures. Fortunately, many animal caretakers, animal technicians and investigators who do the hands-on work with rats and mice and have daily contact with their charges do regard rats and mice as true animals and treat them accordingly, by making their lives as comfortable and bearable as possible (Figures 28-30).
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The combined number of rodents and rabbits used for biomedical research in the United States and Europe is >29,000,000. Of these animals an estimated:
70 percent (>20 million) are kept in US laboratories and
30 percent (>9 million) in European laboratories (Gauthier, 2004; Kaliste, 2004).
Even though most of the rodents and rabbits are used in US research facilities:
less than half (47 percent; 123/260) of the relevant articles pertaining to the improvement of their housing and handling conditions were published in US journals;
more than half (52 percent; 134/260) of the relevant articles were published in Europe.
The outlook for rodents and rabbits kept in research facilities will be more promising in Europe until researchers in the United States seriously acknowledge the fact that improving the living conditions of their animals is a prerequisite for scientifically sound research methodology.
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| Figure 30 Rats are sensitive animals who deserve to be treated with consideration of their well-being. |
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