4,11. Running Wheels

Is there any evidence that access to running wheels can prevent the development or decrease the incidence of behavioral disorders—such as barbering?

Gebhardt-Henrich et al. (2005) found that single-caged hamsters show significantly less stereotypical bar-mouthing when they have access to running wheels. Similar findings have not been published for mice and rats.

Do mice compete over access to one running wheel?

The answer is definitively "No." We have often seen several mice on one running wheel, and never witnessed any antagonism related to the wheel. It's not uncommon to have two mice running in the wheel and one or two, in addition, running on the top of the wheel (Figure 28). It is quite a sight!

Figure 28 Properly sized and designed running wheels provide effective environmental enrichment for rodents. Photo by Maureen Hargaden.

Do "old" rodents have any use for running wheels?

Running wheels are great for young and adult animals who have the energy to exercise. Aged mice may sit in a wheel, but they are unlikely to run in it. I remember a study in which "aged" rats—24 months old—were tested on running wheels. These animals had hardly any use for the wheels. The researcher tested two separate groups of aged rats, and neither of them was interested in the wheels. For old rodents, an object for gnawing and manipulation is a better enrichment idea than a running wheel.

Running wheels provide suitable enrichment for rodents.

4,12. Burrows

I use 10 cm deep carfresh bedding, along with cardboard tubes and nestlets, in regular mouse cages. The mice build amazing nests and dig tunnels in this paper-based substrate. It is quite a revelation to see laboratory mice burrow in substrate. I always have a broad grin on my face when watching mice dig so furiously that they flick the substrate out of the cages and all over the place—a technician's nightmare! The mice build the tunnels along the sides of the cage—touching the sides (thigmotaxis) seems to be reassuring to them—so you can see them running about and behaving in very different ways underground. It's fascinating to watch!

Mice readily work to gain access to a suitable burrowing susbstrate, and they are more motivated to burrow in it than run through a tunnel (Sherwin et al., 2004). This suggests that burrowing constitutes a "behavior need" for them that is not satisfied by an already prefabricated burrow.

We give our rodents lots of shredded paper, straw and/or hay that they tunnel through and use for nesting. However, to check every animal on a daily basis can be a challenge with mice. To take the lids off the cages and search for mice amongst the nesting/burrowing substrate is relatively time-consuming and also probably causes considerable stress for the mice. This is less of a problem with rats who, unless sick, nearly always come to the front of the cages—even if this implies leaving a shelter—to see who is approaching their cage.

Rats will use about anything that can cover them, even if it's not really suitable. I have videotaped a rat who tried hard to dig into and burrow under a handful of wood-wool to become invisible to my presence. It is very important to realize that the domestication of rats has not eliminated their inheritance of being a prey animal. Their sense of security is very much dependent on being able to disappear from sight quickly, either by seeking cover or ducking under in a burrow. Unlike mice, rats will readily accept a prefabricated burrow.

The need to dig a burrow is probably not as strong in rats as it seems to be in mice. In sharp contrast to rats—who are very curious—mice are reluctant to leave their burrow in order to be checked, unless they know you very well and have good reason to trust you.

4,13. Gerbil Idiosyncrasies

I recently adopted two female gerbils who were used to test a new ventilated housing rack. I have them in a snake aquarium—there's no snake in there!—and initially had them housed on aspen chips. Several months ago, I changed their environment completely. I replaced the aspen chips with a 10 cm layer of ground walnut shell, into which I buried a PVC pipe with bends and elbows so that three openings were positioned above the shell. Here are my questions:

  1. The gerbils seem intent on burying their food dish and they seem to do it deliberately: They'll jump in the bowl, sniff about, and then jump out and shovel walnut shell into the food bowl, then repeat the entire procedure. Is there a better way of providing their feed other than spreading it across the cage?
  2. The gerbils move their nesting paper every few weeks to different corners of the tank. Is this normal or does it indicate that something in the environment is stressing them?
  3. How much space do gerbils need? When they were on aspen chips, the tank seemed more than spacious, judging by how much of the space they actually used. Now that they have a digging substrate, they would probably be happy with an enclosure that took over the entire room.

Since gerbils are proficient diggers, I always give them at least 30 cm of substrate, consisting of wood chips, hay, straw and twigs. I also add branches and cardboard boxes to stabilize this substrate. Stable burrow systems can only be constructed if the enclosure is big enough. For your two females, I would recommend living quarters with a floor space of at least 100 x 50 cm and a height of at least 50 cm—the bigger the better.

If the substrate is stable enough, the gerbils will not need an artificial burrow system made of pipes, but they will prefer to construct their own burrow. The burrow will be constantly "under construction" and change practically every day.

Occasionally moving the nesting paper to different places is a biological normal adaptation to the fact that the nest might become infested with parasites, if the animals contact it for too long a time period. I have studied gerbils kept in moist sand-filled tanks that were designed in such a way that I could observe the animals almost everywhere within their burrow system. It turned out that gerbil families change their nest site every three to five days!

The strong urge to bury the food that is not stored in food chambers is also a biologically normal behavior, as food competitors—in the natural environment, especially the steppe vole—might steal it. Even if you scatter the food all over the substrate, the gerbils will first store some in food chamber-like places and then bury the rest. There is nothing you can do about it.

4,14. Shelter and Nesting Material

What kind of shelters and nesting materials work best for rodents and rabbits?

4,14,1. Mice

4,14,1,1. Indestructible Material

We use the commercial plastic mouse house in combination with cotton nestlets. The mice use these shelters regularly. Some investigators noticed a better breeding performance when their mice had access to a mouse house plus a nestlet. As a result of this, most of our mice have now a mouse house along with a nestlet.

My experience with the mouse house is not so favorable. I have noticed that, in a cage furnished both with the house and with paper tissues, mice will typically drag the tissues to a suitable location away from the house, build a nest and sleep in their own nest rather than in the house (Figure 29).

Figure 29 When given the choice C57Bl/6 mice will build their own nest with appropriate materialhere paper tissuesand sleep in it rather than make use of a red plastic mouse house. Photo by Pascalle van Loo. 

I have made a similar observation. Some of our females with pups just don't like this sturdy "mouse house." I would place a mother with her litter in a house, but she would soon move the whole litter out. I repeated this game several times, always with the same result. Some mothers simply refused to stay in these houses and preferred building their nests outside with paper tissues. It's not really surprising that some—perhaps most—mice prefer to construct their own nests according to their mice-specific microclimatic needs, and sleep in them instead of a prefabricated structure.

We have a group of mice who, without apparent reason, showed a decline in breeding performance. After we placed plastic mouse igloos and nestlets in their cages, these mice returned to their normal breeding performance. I have seen some of them take their nestlet into the igloo—where they probably built their nest—and keep their pups under the igloo. Possibly, the mice feel more secluded in the relatively small igloo, while the much bigger mouse house may feel too open for them. The igloo is also less heavy than the big mouse house, and the mice can push it around, adjusting the entrances/exits exactly the way they want them to be.

4,14,1,2. Destructible Material

We have tested cotton nestlets in several strains and found that: MF1 nudes shred them and build nests, and ordinary MF1 and Balb/c mice seem to ignore them; the same is true for C3H mice. Some C57Bl/6 mice shred them or sit on them, while others also ignore them.

With the strains that don't use the nestlets, it's almost as if the mice don't recognize them as nesting material. It might help if you started them off, but it would be quite fiddly, and I don't think the advantages over shredded paper are sufficiently clear to warrant the extra labor, especially when you have several thousand cages to deal with. We have stopped using the nestlets, as all strains of mice that we work with seem to be "happy" with shredded paper. The additional advantage of shredded paper is that it costs nothing.

When given a choice between a paper-based and a plastic nestbox, mice always choose the paper box. Usually they sleep inside this box and, when given nesting material, they drag it into the box and build a nest (Van Loo et al., 2005). When no extra nesting material is available, they will shred the paper box and use the shredded material to build their own nest and sleep in it.

We use hardpaper igloos. The mice climb on them, chew holes in the walls, and mark them with urine, thereby giving a personal touch to their homes. When we move these urine-impregnated igloos during the cage cleaning process to the new cage, the mice are much less restless and aggressive among each other. They probably feel "at home," as it literally smells like home.

I think you are right. We give our mice paper-based nest boxes that we also move along with the animals into fresh cages. The repeated transfer of the soiled nest boxes and the scent marks adhering to them probably accounts for the fact that we also see hardly any fighting in strains considered to be conspicuously aggressive. Over the six years that we have been using paper-based nest boxes, we have encountered no ill effects on the mice's health status.

Our mice get cardboard boxes brought in from home by animal care staff. We first autoclave these items before placing them into the cages. The animals seem to enjoy the boxes, and we like to think we are being "green" by not wasting paper. It often raises a smile to see a gang of rats or mice using an empty cat food box as a house. Who said animal techs don't have a sense of humor! We also use egg cartons, which autoclave very well. The mice explore the little "huts" and quickly turn the cartons into shredded pieces that make a good bedding and can be turned into nests.

4,14,2. Rats

In contrast to mice, rats have a strong preference for solid shelters. They have little use for nesting material unless it comes with a secluded shelter in which the nest can be built. Both female and male rats will move suitable substrate, such as straw, into a shelter and build well-formed nests even when they have never before been exposed to nesting material (Figure 30; Jegstrup et al., 2005). Rats will rest in a shelter during the light period, and climb on it and spend much of the time resting in that elevated position during the light period. Almost any type of solid shelter will do for them, but they seem to have a particular preference for opaque boxes with two or more small entrance holes (Patterson-Kane, 2003).

Figure 30  Rats will move straw into a shelter and build well-formed nests even when they have never before been exposed to nesting material. Photo by Inger Jegstrup.

It is not the general view at the facility I work, but I personally think that an appropriate shelter should be considered basic cage furniture. The majority of our breeder rats prefer rectangular PVC tubes over round pipes, probably because the pipes are not stable enough for quiet resting or sleeping, but easily roll over when the animals play on them and when the cage is moved. Pipes are accepted under the condition that they are firmly attached to a side of the cage (Figure 31).

Figure 31 Round plastic pipes are accepted as sleeping sites under the condition that they are firmly attached to a side of the cage. Such elevated retreats can save rodents from drowning in the event of cage flooding. Photo by Maureen Hargaden.

I also consider a shelter a must for rats and would concur that the animals like small openings that the occupants can "plug" with their rumps. We use cardboard boxes or recycle old polypropylene mouse cages. Both are well accepted by the animals. I have never seen competition or aggression between rats over access to the shelter, although I am always careful to make it big enough for everyone to fit. They usually huddle together in it and very rarely sleep outside, even when they live in relatively large groups.

4,14,3. Hamsters

Our hamsters receive wood-wool, which they quickly turn into fantastic nests. Sometimes animal care staff also provide them with little cotton nestlets, which can be torn up and incorporated into the wood-wool structures. The hamsters are quite content in these nests. I say this because there is no movement in these retreats when personnel enter the room, whereas hamsters without access to such a secluded nesting area get very disturbed and desperately try to hide. I think it is very important to offer hamsters the option of hiding from the human potential predator. Hamsters tend to get hyperaggressive when they are kept in barren cages. An appropriate shelter, offering the caged hamster a "safe" retreat, can mitigate this problem (McClure and Thomson, 1992). They seem to really enjoy short PVC pipes (Figure 32). They typically tip them over and then sleep curled up inside.

Figure 32  Short PVC pipe sections provide appropriate shelters for hamsters. Photo by Gernot Kuhnen.

4,14,4. Guinea Pigs

Like hamsters, guinea pigs have a strong need to hide from the human predator. Their feeling of security depends on access to a covered refuge. PVC pipe sections provide great shelters. Group- and single-housed animals hide in them, run through or jump over them. I am sure they would prefer cardboard boxes, which they could gnaw and which would not roll over, but many of our researchers are concerned that the animals might ingest some of this easy-to-gnaw material, which then could exert an effect in nutritionally sensitive protocols. We have found no evidence that the animals gnaw the PVC pipes.

We use old polypropylene mouse cages with a hole cut out of one wall. They can be removed easily or flipped over when you need to get hold of an animal. Our guinea pigs use these shelters often, especially when people enter the rooms. I do recommend shelters for guinea pigs, because I see the animals making use of them so much, not only for taking refuge and sleeping in them, but also for sitting on top of them to get a better view of the room.

4,14,5. Rabbits

Even though rabbit pens are often furnished with wooden or cardboard boxes, there is no published evidence showing that the animals—with the exception of nursing does—make good use of such boxes as shelters. When we give our rabbits cardboard boxes, they spend a great deal of time sitting or stretched out on top of the shelters rather than resting in them. Once we cut holes in the walls, the animals use these boxes also as shelters and lie inside, looking through the holes.

We house females rabbits in groups of nine and have noticed that, if there are not enough hiding places available, fights are bound to happen. We found that the frequency of such fights is reduced when the animals have access to cardboard boxes that have an entrance and an exit. The doe who chases another doe usually calms down the moment she loses visual contact with her victim disappearing in such a refuge.

4,14,6. Conclusions

The needs of mice and rats for a shelter and nesting material are quite different. Building their own nests is almost a "must" for mice, and the nest will then also be used as a retreat. For rats, access to a solid shelter has high priority, and a nest will be constructed in it when the appropriate material is available; if it is not available, an unfurnished shelter will do. The general well-being of hamsters and guinea pigs is dependent to a great extent on hiding from humans. Rabbits tend to use shelters more as look-outs than dark refuges. In group-housed rabbits, such refuges can help avoid aggressive chases.

4,15. Bedding for Rodents

What is the most appropriate bedding/litter material for rodents?

We use ¾ "dust free" autoclaved softwood sawdust for all our rodents and have not encountered health-related problems in any species or strain, including nude mice. We switched to that substrate after quite a number of our nude mice had developed conjunctivitis on fine sawdust bedding that had a relatively high dust content.

Mice prefer shredded paper and wood-wool over woodchips or sawdust probably because the paper and wood-wool not only serves as bedding but can also be used as nesting material (Blom et al., 1996; Eskola and Kaliste-Korhonen, 1999). Carefresh bedding, which is made of recycled paper, absorbs urine and odors well, is nice for bedding and does not cause skin or breathing problems that some of the wood-based litters do. Another advantage of carefresh is that the mice can build elaborate nests with it.

We use corncob litter which also absorbs urine pretty well. There is no indication that it irritates the skin of our mice, who use the corncob litter not only as a bedding, but also as a foraging substrate.

Having tested different types of bedding for rats, I think there will be little debate when I say that woodchip bedding is the worst. Corncob and smaller wood flake bedding is not too bad, but I like the compressed paper chip the best because:

You have to be careful with hamsters when you give them paper bedding. Hamsters, who are not familiar with paper, will chew and store it in their cheek pouches where it can get stuck easily. Starting already early in life, our hamsters get paper which they do not try to eat, but consistently use to build a nest. When they are adults, there is no risk that they will pouch paper material.

Paper-based substrate seems to provide the most appropriate bedding for mice and for rats.

4,16. Beds for Dogs

Does anyone of you supply some kind of bed for singly housed dogs?

I have the feeling that traditional cages are "uncomfortable" for a dog when he/she wants to rest. I would assume that dogs prefer to sleep in a partially closed-in area—against a wall or in a corner—giving them a sense of security. The addition of two, maybe 5 cm high, Plexiglas barriers to the inside of the cage could perhaps create such a secure rest area for a dog.

This is a great idea! I wanted to do something like that for a long time. I will never forget one experience that showed me that dogs want a "bed" to sleep in: We were switching some runs and it happened that we let the dogs stay a few days in the pig room that was vacant at the time. The pigs' empty food bowls were still there. When I walked into the dogs' temporary quarters the next day, I found almost all of them curled up inside these bowls; it was so cute! The dogs showed me very clearly that they appreciate this type of security. After all, they are den animals and appreciate small spaces, just as pet dogs do, who like to go into their crates to hang out and sleep.

An easy way to make a bed for dogs is to buy plastic dog kennels and use each half as a bed. It provides three sides that are high enough to give the animal a sense of security. Our dogs seem to be happy with these "beds."

There are practical options to provide dogs with a "comfortable" place on which they can rest and feel relatively secure.

4,17. Vertical Space Enhancement

Do caged animals benefit from elevated structures?

4,17,1. Rodents

I have designed for my "leftover" research mice—aka my work pets!—a multi-level caging system, by stacking a standard long mouse cage into a standard rat cage and drilling a single hole in the floor of the top cage, thereby providing an artificial underground space with a deep layer of woodchips (Figure 33). I think it really provides a much improved environment for the mice, allowing them to hide, tunnel and dig, and sleep in seclusion in the lower level during the light hours, and engage in various activities, including wheel running, in the upper level during the dark hours of the day. When they hear me enter the room, the mice always come to the top cage for treats. When they have pups, they keep them strictly in the bottom cage.


Figure 33 This is a species-adequate, custom-made multi-level caging system for mice. Photo by Tamara Godbey.

The cage arrangement that you describe is ingenious! Your observations strongly suggest that mice—I am sure rats also and maybe even guinea pigs—swould benefit from having access to two different levels in their cages, a low-level secluded area for resting during the light period, and a high-level activity area for the dark period of the day.

Nelson et al. (2003) found that rats spend only 22 percent of a 24-hour day on raised platforms. The low attraction of platforms is probably because they expose rather than shelter these prey animals.

4,17,2. Dogs

All our dogs have access to an elevated resting surface. We have mounted a little platform on one side of each cage. It can be flipped up against the wall, so that there is more room when we clean the cage. This simple system works well for us. The dogs seem to like their platforms, jump on them and have a good view of what is going on in the room or sleep on them (Figure 34a, b)

Figure 34a,b This elevated resting surface for dogs is a custom-made platform that can be flipped up against the wall to create more room during cleaning and to allow the water to run off quickly from it (a). Dogs will "even" sleep on their bench (b). Photos by Aziz Cetinsu.

Raised resting surfaces are liked by dogs. They provide some degree of security, increase the dog's ability to view outside the cage, and increase the overall area available to the dog. I have noticed that dogs who have access to a platform are more approachable, friendly and playful.

4,17,3. Primates

Primates are biologically adapted to spend most of their time—especially the night—above the ground. The vertical or arboreal dimension is safer for them and, when having the choice, they will spend more time on elevated structures than on the ground both in the wild and in captivity (Bernstein and Draper, 1964; Bennett and Davis, 1989; Reinhardt, 1992b; Ochiai and Matsuzawa, 1999; Buchanan-Smith et al., 2002; Taylor and Owens, 2004; Clarence et al., 2006; Ross and Lukas, 2006). Providing primates with high resting surfaces, therefore, seems crucial for their overall well-being in the research lab setting.

When I release our cyno males into their play room, they will typically spend most of their time on the highest structures available. They may come down to explore a toy briefly but will quickly return to a "safe" high place (Figure 35).

Figure 35  This is a play room where two male cynos spend most of their time on the highest climbing structures. Photo by Richard Lynch.

We keep a group of 18 Japanese macaques in a 13 m high tower that has a 115 m2 floor space and is equipped with various structures installed at different levels (Figure 36). Systematic observations revealed that individuals spend on average more than 80 percent of the day time on structures 4 m or higher above the ground.

Figure 36 At this Frame-Kit Tower for Japanese macaques at the PRI, Kyoto University, monkeys spend more than 80 percent of their time on structures at a level of 4 m or higher. Note the two monkeys on top of the tower. Photo by Yoshikazu Ueno Yoshi.

Our group-housed cynos became much more compatible after we installed elevated structures in their enclosures. Nakamichi and Asanuma (1998) and Neveu and Deputte (1996) also noticed in Japanese macaques and mangabeys, respectively, that placing high perches in their pens decreased agonistic interaction, probably because the perches allowed the animals to keep social distances as needed.

Do macaques have a preference for fixed perches versus suspended perches?

Most of the primates' natural environment is "fixed." Even a tree is "fixed;" it's only at the end of branches where a monkey in nature would have the sensation of anything like a swinging perch. A fixed perch is a great thing for a monkey. We used to hang numerous swings and movable raised structures into the enclosure of our group-housed cynos, but we could see very clearly that they prefer the stable perches or platforms. Our animals very rarely used ropes or swings. The only ones using those elements were babies and juveniles.

I gave adult rhesus macaques the choice of sitting on a PVC pipe suspended in the center of one section of a double cage, and a PVC pipe of the same diameter mounted diagonally at the same height of the swing in the other section of the double cage. The animals used the perch almost eight times as much as the swing (Kopecky and Reinhardt, 1991). The preference for the perch was probably related to the fact that, unlike the swing, it was a fixed structure permitting continuous relaxed postures rather than short-term balancing. Moreover, the perch, unlike the swing, allowed the monkeys to sit right in front of the cage and have visual control over what is going on in the room.

In the small standard cage, a swing cannot really be used for swinging—there is just not enough room for that—but macaques typically use them to produce a lot of noise, by slamming the swing against cage walls. This is perhaps a great acoustical enrichment for the animals but certainly not for the attending staff!

When they have a properly placed resting surface, such as a comfortable perch, do macaques spend the night resting on them?

Our group-housed rhesus macaques have access to perches at about 1.2 m off the ground. On some occasions, I have checked on them during the night and have always found them sleeping on the perches. I have never seen them sleep on the ground. A similar observation has been made by Van Wagenen (1950) who reported that sitting on a board approximately 1 m off the ground was the favorite position of single-caged rhesus macaques, and that the animals slept on the board at night.

Is it necessary to install resting surfaces as high as possible in the primary enclosure?

Yes, definitively! For example, a platform is very desirable for capuchins, but it must be placed as high as possible so that the monkeys can watch for predators from a safe location. High resting surfaces are used by the animals extensively. If they have blankets or similar texture available, they will sleep on their platform with the blankets pulled over their heads!

In the caging systems we use, there is no bottom tier. All cages are 0.6 m off of the floor. Each cage is furnished with a 1 m high perch, so it is pretty much at human eye level—1.6 m height. It seems to me that the animals feel relaxed when they sit on their perch and can meet me at eye level. A low perch has little or no value as a "safe" resting location from our monkeys' point of view.

What is true for capuchins is certainly also true for other monkeys, simply because all of them avoid ground predators, by climbing up trees and spending the night well off the ground in trees or rocky outcroppings (De Vore and Hall, 1965; Hamilton, 1982; Caldecott, 1986; Altmann and Altmann, 1970; Lindburg, 1971; Roonwal and Mohnot, 1977; Di Bitetti et al., 2000). For monkeys height is a major antipredator factor, determining the location of their "dormitories" in the natural habitat, and the presence of some large trees often seems to be the only limitation to their adaptation to a particular environment (Simonds, 1965; Anderson, 2000). Rhesus macaques, for example, sleep in trees sitting on branches, mostly in clusters of two to three monkeys huddled together (Vessey, 1973). A low perch would be of little value to them in the research lab setting. Yet, the placement of resting surfaces at a very low level is legally condoned by the US Animal Welfare Act Regulations (United States Department of Agriculture, 2002) and also by the US Guide for the Care and Use of Laboratory Animals (National Research Council, 1996). Both texts have included the following clause:

This legal loophole is probably the reason why built-in perches or ledges are usually installed at a height of only 20 to 30 cm, regardless of the fact that such a low resting surface can block part of the minimum floor space of standard cages that would be required by an animal to turn around freely and make normal postural adjustments (Figure 37). This situation is very unfortunate for the animals and does not have a parallel in any other country.

Figure 37  In American primate research facilities, perches are often placed in such a way that they block part of the floor area that the caged monkeyhere baboonswould need to freely turn around. Photo by Viktor Reinhardt.

4,17,4. Conclusions

Under normal circumstances—when the cage is not flooded—rodents do not necessarily benefit from a raised platform, unless it also provides cover. Elevated resting surfaces are beneficial for dogs and primates, especially at times when their enclosure is hosed down and the animals can "escape" to a dry place (Figure 38). Given their adaptation to an arboreal life style, a high fixed resting surface should be a basic furniture of every primate cage.


Figure 38 A high perch allows this male rhesus monkey to meet the caretaker at "safe" eye level and sit on a dry place while his cage is rinsed with water. Photo by Viktor Reinhardt.

4,18. Environmental Enrichment for Ferrets

There is very little published information on the species-appropriate housing of ferrets. Can anybody share first-hand experience on this issue?

There have been six ferrets at our facility who have since all been adopted out. It struck me that these animals had very short attention spans, so it was important to have a variety of toys and to rotate them frequently. You do not have to spend a lot of money to make ferrets happy. Empty bedding bags were a great hit! They also enjoyed rolling around small cat balls with bells in them, though they destroyed them rapidly and, hence, needed frequent replacements. They also enjoyed playing "tug of war" with a hanging rabbit carrot toy. A large hanging bird bell fascinated them quite a bit. They seemed to be particularly attracted to the ringing, as they would run over to you, if you jingled the bell. One of their favorite toys was a green gummabone. As soon as one of them would pick up the bone, the others would chase him and try to get it.

From what I have heard, ferrets are commonly housed on gridded floors in modified rabbit or cat cages. We housed ours on aspen shavings in a standard pet ferret cage surrounded by a plastic playpen, the kind you can buy at a pet shop as a puppy enclosure. The ferrets used the litter box only occasionally. They would not drink from water bottles, so we gave them ceramic water bowls and discovered that they also like "fishing." We filled a litter pan with approximately 3 cm of water and put floating and sinking items in the pan. One of the ferrets would actually submerge his entire head! For "hammocks," we used surgical drapes and attached them to the rungs of the cage. Typically, the animals slept in a pile either inside a box or in a clean litter pan. We were concerned that they would climb out of the enclosure and get into trouble in the room, but we found that the only time they scaled the wall of their enclosure was when people were in the room playing with them. They loved being held!

4,19. Environmental Enrichment for Guinea Pigs

Is it too messy to provide guinea pigs with hay on a permanent basis?

In my experience, loose hay autoclaved at 220º F for 5 minutes is the best enrichment for guinea pigs. I have used it successfully for a decade with our animals. They nest and hide in the hay, and they eat it. They will trill when you bring them new hay. Their excitement shows you that hay is a species-appropriate enrichment for them.

We keep our group-housed animals in recycled rabbit-cages with perforated floors. Each cage is furnished with a Macrolon Typ IV rodent cage that has sawdust bedding with a generous layer—about 8 cm thick—of hay (Figure 39). The animals "tunnel," hide and sleep in the hay. On top of that, hay is a favored foraging substrate for them. I do not find that hay creates a mess. Guinea pigs like to have a clean sleeping area. They jump out of the Macrolon cage and defecate and urinate in a corner of the rabbit cage, in which they also find water and food pellets. We have worked with this cage design many years, and I think the guinea pigs are no less satisfied with it than we are.


Figure 39  An old rabbit-cage, furnished with a rodent cage that is provisioned with sawdust topped with hay, provides species-adequate enrichment for guinea pigs. Photo by Richard Weilemann.

Our large breeding groups live in floor pens. For enrichment, hay is placed in plastic barrels that have holes in the bottom. Since guinea pigs love to go under anything that covers them, we mount the barrels on approximately 20 cm high iron legs, allowing the animals to run under the barrel. This arrangement also provides foraging enrichment, and the animals skillfully pull strands of fresh hay through the holes in the bottom of the barrel. The only occasional problem we have had with hay was when guinea pigs were tethered and long blades of hay would wrap around the cannula. We now prevent this by simply chopping the hay for cannulated animals into short (about 15 cm) blades.

Our singly caged guinea pigs have PVC tubes or paperboard oat containers—when the guys are too big to fit through the PVC—through which they run and over which they jump. They seem to enjoy this and do it constantly, suggesting that the novelty effect of these short tunnels does not wear off. Other than that there is really not enough space in the cage to add any other enrichment object. We also try to address their social needs by housing them in transparent cages and arranging the cages in such a way that the animals can see each other. This also implies that they can keep vocally in touch with each other, which they certainly do pretty much most of the time.

Guinea pigs do not manipulate their food, but pick it up directly from the ground with their teeth. This suggests that any toy-like enrichment gadgets that may be useful for rats, mice, hamsters or rabbits serve no purpose for guinea pigs, especially those who are kept in single-cages. My pet guinea pig, whom I adopted after he was released from research, does not care to play with any toy-like enrichment gadgets, but loves to chase my hand and then run away from it. I wish I had the time to do this also with the animals in the lab!

Hay and tubes provide suitable enrichment for guinea pigs. To minimize the distress resulting from being alone (Fenske, 1992; Lazaroff et al., 2006), a guinea pig should always be housed in such a way that the isolated animal can keep vocal contact with conspecifics.

4,20. Environmental Enrichment for Rabbits

What are the most effective, yet practicable enrichment options for rabbits?

Branches provide inexpensive enrichment. The rabbits spend quite some time gnawing at the bark, but once all the bark has been removed, the branch is of no more interest to them. Hay is more attractive for the animals and more practicable for the personnel. Our rabbits do not get tired of nibbling and eating this natural foraging substrate. Presenting the hay on the top of the cage is a particularly simple but very effective way of providing species-adequate environmental enrichment—strictly speaking "feeding enrichment," because the rabbits are given the opportunity to engage in foraging behavior. Offering the hay in a "hanging manger" is equally useful (Weaver, 2004).

We autoclave the hay at 120oC for our specific pathogen-free (SPF) rabbits. The hay does change its color and takes on a smell that is difficult to describe, but this does not seem to bother the rabbits who still eat it with gusto.

Toys, especially durable toys, are of little use for rabbits (Harris et al., 2001; Johnson et al., 2003) unless they are replaced constantly. If you have to replace toys all the time to prevent habituation and subsequent boredom, the question arises, if the term "environmental enrichment" is really appropriate for them. Probably not.

I entirely agree. Enrichment should meet the rabbits' behavioral needs. Durable toys do not meet those needs.

There are exceptions: The rabbits in my charge get a lot of entertainment by pushing metal jar lids along the floor and moving the shavings out of the way.

Yes, jar lids, either loose or suspended on a chain, provide great enrichment for caged rabbits. They show keen interest in these gadgets for prolonged periods of time (Bell, 2000). If one rabbit picks up the lid and drops it—or if a person picks one up and drops it—within moments all the rabbits in the room will come and join playing with the lid. They push it around energetically, thereby creating quite a noise. Small bells hung from the ceiling of the cage, are similarly attractive. Our bunnies love these and will nose and push them during long play periods.

Hollow plastic cat toys with bells inside are also great enrichment gadgets. I guess it is the noise of the bells that makes these toys so attractive. Our rabbits play with them over long periods of time. I also have witnessed the domino affect, with one rabbit starting to play and the other(s) promptly joining. When I pick up the toy and toss it, sure enough, one of them will fetch it—just like a dog—and bring it back to me. I will toss the toy again, and this game can go on and on. These cat toys have been a big hit and the rabbits never seem to lose interest in them. The bell inside gets rusty after a while, and some of the rabbits chew on the toys and finally destroy them, but they are not expensive and we replace them as needed.

We give our rabbits autoclaved cardboard boxes, which the animals use not so much as hiding places but as lookout posts. They spend much time sitting on top of the boxes and spy out the land, but they also tear holes in the sides and then spend hours playing tag in and out of the holes. When the box finally collapses after about a week, we just throw it away and replace it with a new one. Our staff saves boxes, so this kind of enrichment costs nothing apart from the effort of collecting and distributing it.

If they can trust you, rabbits enjoy human contact. The rabbits in my charge climb on anyone who visits them, pets them and distributes treats. This is a perfect form of entertainment, not only for the rabbits, but also for the staff and students who volunteer to socialize with these animals.

Hay provides the perfect environmental enrichment for rabbits. Objects that the animals can push and that make some noise, while being moved around, can entertain rabbits for long periods of time. Regular positive interactions with humans provide optimal social enrichment for rabbits.

4,21. Environmental Enrichment for Pigs

What kind of environmental enrichment works best for pigs?

Figure 40 These are custom-made suspended toys for pigs. Photo by Tamara Godbey.

After hearing a recommendation of chain-toys for pigs, I made my own: I use about 75 cm lengths of heavy metal chain with assorted dog toys attached to the middle or end of it. The toys include Booda rope, the pigs' favorite toy (Figure 40), nylabone rings, kong toys and rubber bones. I attach these toys to the chain with metal clips so that they can be easily removed and rotated from pen to pen. I can hear the pigs rattling their chains and toys when I leave at night and when I come in on the weekends. Whenever I enter the pig runs, I can always see a pig or two with the toys or chains in their mouths (Figure 41). I gave our pigs their toys four months ago. They still use them, and there are no signs that they have lost interest in them. It just makes sense that they need something to mouth as they chew on each other all day long—and chew on me when I enter the pen!

Figure 41 Chewing a toy is probably more species-appropriate than stereotypically chewing pen fittings. Photo by Tamara Godbey. 

It is my experience that pigs display far more species-typical behaviors and are less restless—no longer bang at the door—when they have access to kong toys, hanging rubber tires and cloth strips than when they are kept in barren enclosures. The kong toys are a great hit. We replace them twice per week so that they can be cleaned—pig saliva tends to be very difficult to wash off once it dries onto/into the rubber material. I have to come with a new kong toy, plus scratch the pig, so that she reluctantly releases the kong that I need to get out for cleaning. Rubber tires or cloth strips also provide great enrichment, however, I have noticed that pigs housed on crates, rather than bedding, tend to lose interest in these items. For these pigs we rotate the tires and strips about every ten days to enhance novelty.

Each of our pigs has access to a 15 cm deep wooden tray filled with sawdust that we top every day with fresh straw. The animals spend more time "rooting," chewing the straw and playing with the straw than they do with any of the toys we have ever given them (Figure 42). Straw seems to be the perfect enrichment substrate for them, and there is no indication that they will ever get bored from it. Spoolder et al. (1995), Whittaker et al. (1998) and Scott et al. (2006) have shown that the provision of straw prevents the development and reduces the incidence of stereotypical oral activities, such as chewing pen fittings, in pigs.

Figure 42 Straw provides optimal environmental enrichment that pigs do not get bored of over time. Photo by Diane Halverson.

We have attached a "scrubbing brush" on the side of every pen, so that our pigs can scratch those itchy spots! Since most pens are smooth stainless, or the walls are smooth tile, the pigs usually do not have an opportunity to rub against anything. The scrubbing brush does not lose its attraction over time, probably because it offers great relief from itching. Our pigs also get discarded linens, which they like to shake and carry around but, fortunately, never try to ingest.

Well-treated pigs don't get tired of human contact. Our animal techs spend quite a lot of time just "popping" in to say hello and to give their animals a scratch, which they always seem to appreciate a lot.

Within the given constraints of single-housing, straw provides optimal species-appropriate enrichment of which pigs do not get bored, because it allows them to engage in rooting, foraging, chewing and playing. Toys are best suspended with chains so that they do not get in contact with the manure. Given the strong social disposition of pigs, human companionship is probably the most appreciated form of environmental enrichment for the singly housed animal.

4,22. Environment Enrichment for Fishes and Frogs

Just curious, is anyone providing enrichment for fish or frogs?

Our frogs get PVC tubes in which they hide upside-down plastic boxes, rocks and bricks on which they climb, and plastic litter boxes filled with water serving as little pools. Brown and Nixon (2004) tested frogs in tanks that were empty in one half and furnished in the other half with plastic pipes, an upside-down plastic box with entrance, plastic aquarium foliage, rocks, wood, lid cover or gravel. The frogs showed a clear preference for the tubes, followed by the foliage, the rocks and wood, the box and finally the lid cover (Figure 43). They were not at all attracted by gravel.

Figure 43 Tubes and floating foliage provide species-adequate shelter for Xenopus laevis. Photo by M.J. Brown; reproduced with permission of the Institute of Animal Technology; published in Animal Technology and Welfare 3, 87-95, 2004.

For our fish, we place PVC pipes in the tanks. We have bottom dweller-type fish. They get really spooked if they do not have a place to hide. It also helps with males, who are territorial, but you have to place enough pipes in the tank to avoid competition. We also float pieces of black trash bags on top of the water to create hiding places.

The best enrichment I can think of for fishes are oxygenating plants, e.g., Anacharis and Cabomba. These plants release oxygen into the water, and the fish like to graze on them. They yank off pieces as if they were horses in a pasture. The plants also give the fish a more complex environment—navigating through the fronds, etc. I just let these plants float; they will send out roots even without being potted.

Empirical evidence suggests that objects under, in or behind which they can retreat or hide provide suitable environmental enrichment for frogs and some fish species commonly found in research labs.

5. Social Housing

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