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There are a number of species of hamsters, but the Syrian or golden hamster (Mesocricetus auratus) is the species that is most commonly found in research institutions. The entire laboratory and pet population of the golden hamsters appear to be the descendants of a single brother-sister pairing. These littermates were captured and imported from Aleppo [Syria] by Aharoni, a zoologist of the University of Jerusalem in 1930. In Jerusalem the hamsters were bred very successfully. Years later, animals of this original breeding colony were exported to the USA, where golden hamsters started to become one of the most popular pets and laboratory animals (Figure 1). Comparative studies of domestic and wild golden hamsters have shown that there is a drastically reduced genetic variability in the domestic strain. However, the differences in behavioral, chronobiological, morphometrical, haematological and biochemical parameters are relatively small and fall into the expected range of interstrain variations in other laboratory animals (Gattermann, 2000).
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There are excellent books on the care of laboratory rodents, but they are dealing more with the demands of the experimentator than with the needs of the experimental animals. In this chapter, the focus is shifted and recommendations made on how to address the golden hamsters' basic behavioral and physiological needs under the constraints of confinement. To meet these needs is to assure the animal's well-being and the validity of research data collected from them.
The original habitat of the golden hamster is the elevated plain around Aleppo in the northeast of Syria. The climate in the summer is hot and dry during the day and cold during the end of the night and the early morning. The winter is wet and cool, and there may be some days with snow and temperatures below 0oC.
Hamsters are solitary animals. They dig burrows, create nests and will hibernate if the temperature becomes low. Golden hamsters are "real" hibernators who lower their body temperature close to the ambient temperature [but not below 0oC]. This kind of thermoregulation drastically diminishes the metabolic rate to about five percent and helps the animal to considerably reduce the need for food during the winter. The burrow buffers extreme ambient temperatures, offers relatively stable climatic conditions, and protects against predators. Golden hamsters dig their burrows generally at a depth of 0.7 m (Gattermann et al., 2001). A burrow includes a steep entrance pipe [4-5 cm diameter], a nesting and a hoarding chamber and a blind ending branch for urination. Hamsters use their fore and hind legs as well as their snout and teeth for digging. Laboratory hamsters have not lost their ability to dig burrows (Kuhnen, 1986). In fact, they will do this with great vigor and skill if they are provided with the appropriate substrate (Editors' note).
Hamsters are nocturnal rodents who are active during the night, busily searching for food like fruits, vegetable, grains, worms and insects. They carry and hoard the food in large cheek pouches.
The golden hamster uses so-called flank organs [glands located in the hip region] for territorial marking. The territory is defended against conspecific intruders with overt aggression. Hamsters are vicious fighters and show little inhibition to inflict serious injuries. Females are bigger than males, and they are also more aggressive. Non-aggressive social contact among hamsters seems to be restricted to the brief instance of copulation and the period of lactation.
The environments of laboratory animals are usually designed on the basis of economic, hygienic, ergonomic and research aspects, with little consideration of animal welfare. Poor housing conditions can affect normal physiological responses and inhibit the expression of species-typical behaviors that are essential to safeguard the well-being and behavioral health of the animal.
Any housing system for hamsters should satisfy the physiological and ethological needs for resting, nest building, grooming, exploring, climbing, hiding, digging, searching for food, hoarding and gnawing.
Cage size
Legal minimum cage size specifications are not satisfactory because they are based on an individual animal's body weight, with more space being allocated to heavier - and hence older - animals than to lighter, younger animals. This simplistic formula fails to take into consideration that young, relatively light hamsters are highly motivated to engage in energetic exploratory and play activities requiring extra space. Keeping them in small cages results in chronic stress as measured in an impaired febrile response, i.e., increased baseline core temperature and a reduced temperature increase in response to the administration of a fever-inducing substance. Comparing the febrile response of hamsters housed in different cage sizes indicates that a hamster should not be kept on less than 800 cm2 [124 in2] floor space (Kuhnen, 1999a). To house hamsters in smaller cages may jeopardize sound interpretation of experimental results.
Breeding females should be kept in primary enclosures that provide no less than 1800 cm2 [280 in2]. The female hamsters should not be handled or disturbed from about 2 days before to 7 days after parturition.
The importance of cage space for hamsters can also be deduced from anatomical differences indicating a higher fitness [bigger lungs and bigger hearts] of hamsters housed in relatively large cages versus hamsters housed in small cages (Kuhnen, unpublished findings). Housing hamsters in relatively large cages is not only directly beneficial for the animals but also indirectly by decreasing the interval of the extremely stressful cage cleaning procedure (Kuhnen, 1999a; Gattermann and Weinandy, 1996; Conn et al., 1990).
In the typical bipedal position (Figure 1) golden hamsters reach a height of about 16 cm. The primary enclosure should, therefore, have a minimum height of 17 cm [6.7 in].
Hamsters organize their quarters into separate functional areas: a sleeping nest with adjacent larder, a separate urination spot and an area for climbing and exploring.
Cage material and design
The caging material must be smooth, impervious to moisture and liquids, corrosion resistant, easy to clean and durable to withstand hamsters from gnawing through. Stainless steel impairs the hamster’s visual orientation, may produce unpleasant noises and can create an uncomfortable ambiance due to its high thermal conductance, but it can offer the animal some shelter in the dark corners. Polycarbonate seems to be the better choice, because it allows the hamster to see what is going on outside the cage and enable care personnel to readily check the animal. Polycarbonate, however, does not offer the hamster any shelter. This drawback can be overcome with self-adhesive black foil patterns fixed on the outside surface of the cage walls and shelter-providing structural enhancement gadgets, such as sections of PVC tubing and small cardboard tubes or boxes (Figure 2).
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Hamsters are very keen to get out of their cages. The cage lids must therefore fit securely to prevent escapes. Golden hamsters are extremely good climbers and like to use the wire lids for gymnastics.
Hamsters show a strong preference for solid-floor cages with bedding over barren, wire-mesh floored cages (Arnold and Gillapsy, 1994). The animals should, therefore, be housed in obviously more comfortable solid-floor cages with bedding (cf., National Research Council, 1996).
Bedding
The bedding should allow digging and nest-building behavior, absorb urine, smells and toxins [particularly ammonia, which is very irritating to eyes and airways] and keep the hamster clean and dry. Dust-free woodchips or a combination of granulated softwood/filtered sawdust and dust-free woodchips are a good compromise between behavioral and hygienic needs. The change of bedding and/or cage induces a strong stress response in hamsters (Kuhnen, 1999a; Gattermann and Weinandy, 1996). In order to buffer some of the stress, the animal should always be allowed to retain some of the old, familiar nest material (Baumans, 1998).
Shelter and Nest
Hamsters are nocturnal animals who spend most of their time in a dark, secure burrow. Under laboratory housing conditions, direct, bright illumination must be avoided and crepuscular or dark retreat areas provided. They need to have access to a proper place of refuge and appropriate material and space to build a sleeping nest with adjacent larder. A simple, U-formed, opaque structure made of plastic material can serve as a suitable shelter, which is often used also as a nest site (Figure 3). In contrast to the closed nest box, the U-formed shelter permits care personnel to visually check the hamster without causing any disturbance. In order to construct a comfortable nest, the hamster should be provided with hay or wood-wool, paper tissue and a small tube of cardboard (Figure 3). For a hamster, nesting material is similarly important as is food and water, and he will readily work to get access to it (Jansen et al., 1969).
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Supplemental food
To satisfy the foraging, food processing and hoarding drive of hamsters, natural food like grain, seeds, peanuts, carrots, root vegetables and pieces of apple should be distributed frequently on their bedding in addition to the standard food ration.
Enrichment devices
During the night
hamsters have a very strong urge to actively interact with their
physical environment. They should have access to different kinds
of tubes [diameter equal or more than 4 cm] stimulating explorative
behavior (Figure 4) and indirectly increasing the useable floor
space by providing additional wall contact and refuge. The provision
of tubes can be an effective means to resolve aggressive behavior
problems such as growling, hissing, aggressive posturing toward
humans, destruction of water bottle rubber stoppers and attacking
objects introduced into the cage (McClure and Thomson, 1992).
The value of exercise wheels is still debated. The hamsters' intensive
running in the wheel may simply be a locomotor stereotypy. The
demand for a running wheel decreases with increased cage size,
suggesting that rather than fostering stereotypical wheel-running
in small cages, hamsters should be allowed to express their urge
to move around in sufficiently spacious cages.
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Hamsters should always have access to pieces of soft wood to satisfy their need for gnawing and prevent overgrowth of their teeth.
The positive effects of enriched housing on problem-solving tests is well documented since the experiments of Hebb (1947) in rats. In hamsters, environmental enrichment improves the febrile response to restricted cage space without a side-effect on the dispersion of the measured values (Kuhnen, 1999a). Behavioral tests indicate less fear and a better orientation (Kuhnen, 1999b) and improved spatial perception and discrimination (Thinus-Blanc, 1981) in golden hamsters housed in enriched cages.
Single-housing versus social-housing
Unlike all other animals commonly found in research facilities, golden hamsters are a strictly solitary species. Living in groups is artificial for mature hamsters. Enforced group-housing will result in severe and chronic social stress (Meisel et al., 1990; Zimmer and Gattermann, 1996) and a higher rate of wounding (Arnold and Estep, 1990). It is possible to keep immature male siblings in unisexual groups without unduly jeopardizing the animals' safety.
When in oestrus, the female hamster usually gets agitated and accepts copulation from any sexually competent male. She will exhibit lordosis as a clear sign of receptivity. If not receptive, females are likely to attack and possibly kill males. It is favorable to set a receptive female into the territorially marked cage of a male to give the male the advantage of being on his own turf. The female - if fully receptive - will be less inclined to be aggressive under this circumstance. A male who is older, heavier and more experienced than the female has a good chance of not being beaten up. In consideration of the male's safety, the female has to be removed right after mating and returned to her own cage.
Daily visual, unobtrusive inspections of caged hamsters are important to notice pain, suffering or injuries in time so that prompt treatment can be initiated. The following signs are indicators that a hamster is not well:
A healthy golden hamster will typically go through the following ritual when waking up: stretching and yawning with fully opened mouth followed by grooming.
Hamsters are nocturnal animals who instinctively avoid being touched by man. It is therefore important to gently wake a hamster up before manipulating him or her during daytime hours. This not only helps to prevent data-influencing stress reactions, but a startled hamster is frightened and may react aggressively to the disturbing intruder. Hamsters are readily tamed and habituated to gentle handling (Figure 5). Regular gentle handling of a research hamster is no waste of time but will pay off in more reliable research data.
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| Figure 5. Golden hamsters readily overcome their instinctive fear of humans when they are regularly handled with gentleness. |
Arnold CE, Estep DQ 1990. Effects of housing on social preference and behaviour in male golden hamsters (Mesocricetus auratus). Applied Animal Behaviour Science 27, 253-261
Arnold CE, Gillapsy S 1994. Assessing laboratory life for golden hamsters: social preference, cage selection, and human interaction. Lab Animal 23, 34-37
Baumans, V 1998. Enrichment bei Labormäusen: Eine Sache für Mäuse und Menschen. In Tierlaboratorium 21 Juhr NC, Hiller HH, Scharmann W (eds), 59-62. Zentrale Universitätsdruckerei, Berlin, Germany
Conn CA, Borer KT, Kluger MJ 1990. Body temperature rhythm and response to pyrogen in exercising and sedentary hamsters. Medicine and Science in Sports and Exercise 22, 636-642
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Gattermann R 2000. 70 Jahre Goldhamster in menschlicher Obhut - wie groß sind die Unterschiede zu seinen wildlebenden Verwandten. In Tierlaboratorium 23 Juhr N-C, Hiller HH, Scharmann W (eds), 86-99. Zentrale Universitätsdruckerei der Freien Universität, Berlin, Germany
Gattermann R, Fritzsche P, Neumann K, Al-Hussein I, Kayser A, Abiad M, Yakti R 2001. Notes on the current distribution and ecology of wild golden hamsters (Mesocricetus auratus). Journal of Zoology 254, 359-365
Hebb DO 1947. The effect of early experience on problem-solving at maturity. American Psychologist 2, 306-307
Jansen PE, Goodman ED, Jowaisas D, Bunnell BN 1969. Paper as a positive reinforcer for acquisition of a bar press response by the golden hamster. Psychonomic Science 16, 113-114
Kuhnen G 1986. O2 and CO2 concentrations in burrows of euthermic and hibernating golden hamsters. Comparative Biochemistry and Physiology 84A, 517-522
Kuhnen G 1999a. The effect of cage size and enrichment on core temperature and febrile response of the golden hamster. Laboratory Animals 33, 221-227
Kuhnen G 1999b. The effect of housing conditions on the results of behavioural tests in golden hamster. Zoology 102 (Supplement 2), 84
McClure DE, Thomson JI 1992. Cage enrichment for hamsters housed in suspended wire cages. Contemporary Topics in Laboratory Animal Science 31, 33
Meisel RL, Hays TC, Del Paine SN, Luttrell VR 1990. Induction of obesity by group housing in female syrian hamsters. Physiology and Behavior 47, 815-817
National Research Council
1996. Guide for the Care and Use of Laboratory Animals, 7th
Edition. National Academy Press, Washington, DC
Full Text: http://www.nap.edu/readingroom/books/labrats/
Thinus-Blanc C 1981. Volume discrimination learning in golden hamsters: effect of the structure of complex rearing cages. Developmental Psychobiology 14, 397-403
United States Department
of Agriculture 2000. Animal Welfare Report - Fiscal Year 2000.
U.S. Department of Agriculture - Animal Care, Riverdale, MD
Full Text: http://www.aphis.usda.gov/ac/awrep2000.pdf
Zimmer R, Gattermann R 1996.
Der Einfluß von Haltung und Rang auf die Nebennierenaktivität
männlicher Goldhamster (Mesocricetus auratus). Zeitschrift
für Säugetierkunde 61 (Sonderband), 74-75
Dr. Gernot Kuhnen is lecturer at the Physiological Institute of the University of Giessen, Germany, and head of the 'Büro für Thermophysiologie'. He is a biologist and has worked for many years with hamsters studying hibernation, thermoregulation and housing systems.