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in Research Institutions Washington, DC 20007, USA |
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in Research Institutions Washington, DC 20007, USA |
Guinea-pigs are domesticated, conspicuously docile, social rodents originating from South America. Emitting squeaky contact sounds like little pigs is the explanation for their misleading name. They live in small groups of five to ten individuals. Even though they do not groom one another, guinea-pigs seek each other's bodily contact during periods of rest. Scent marking with urine squirted on the coat of another partner, and scent marking with secretions from perineal and supracaudal glands rubbed on the substratum reflect the animals' relative social status and social roles within the group. Strange individuals are recognized by the absence of group-characteristic scents (Reinhardt, 1971).
The young are born after a relatively long gestation period of about 66 days. Unlike other rodents, guinea-pigs do not construct nests. In fact, the newborn are so precocial that they do not need a nest. They look like small-sized adults and start nibbling and eating solid food on the day of their birth. Young guinea-pigs - unlike adults - are very active and engage in exuberant running-and-hopping games alone or with other peers. However, the stage of infantile gamboling is very brief. Young females may successfully breed when they are only three weeks old and give birth to their first litter at the age of three months. Young males engage in sexual courtship activities also in their third week, and by doing so become sexual competitors for the boss male of the group who will target them with persistent chasing. In this way, young males gradually become sexually and behaviorally inhibited unless they are removed from the group (Reinhardt, 1971).
Guinea-pigs neither compete over food nor do they hoard food. This leaves little reason for aggressive disputes. Females never engage in fighting and only rarely do they have harmless squabbles with each other. They get along with each other so well that they even practice communal nursing. In sharp contrast to rats, mice, gerbils and hamsters, guinea-pig mothers do not seem to care much about their own offspring. They neither groom their young nor will they defend them if need arises. If several females have newborns, a naïve observer is not able to tell from the animals' behavior which offspring belongs to which female, because the mothers treat all the young equally and the young suckle from any lactating female. Guinea-pig mothers nurse for no longer than three weeks. During that period of lactation they are tolerant nurses for all – not only for their own – infants of the group. It is the lactating female - not the young - who sets the timetable for nursing. If she feels ready to nurse, she will get restless and walk back and forth thereby attracting the attention of all infants, who will gather and follow until the `nurse' squats on her favorite location and tolerates being suckled. Once she has started, the nurse will butt away any straggler even if it happens to be one of her own progeny. After about ten minutes, she will abruptly walk away leaving a heap of perplexed young. Even though females seemingly do not develop a bond with their offspring, the presence of suckling young makes them aggressive toward strange females (Reinhardt, 1971).
Males are inhibited to show any kind of aggression – including threats – against females, but they viciously fight with each other in the presence of oestrus females. Usually, there is one male who monopolizes such females; his strong dominance keeps all other males in a state of social distress most of the time. In order to prevent attacks, subordinate males behave like females and stop emitting male-typical pheromones. The dominant male treats such 'frustrated' subordinates like females and displays courtship rather than aggressive behaviors (Reinhardt, 1971).
Adult guinea-pigs measure up to 30 cm in length. For the stretching posture they need approximately 3 cm additional horizontal space to allow free expression of this comfort behavior (Figure 1). They are poor diggers but greatly enjoy burrowing in hay. Vocalization plays an important role in their social and sexual behavior. There is always some purring, whistling, squeaking or teeth-chattering to be heard in a guinea-pig room, and a friendly caretaker can count on receiving a noisy welcome. Like most other rodents, guinea-pigs are susceptible to noise stress (Anthony et al., 1959).
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Guinea-pigs are relatively heavy rodents – with adults weighing about 1 kg – and are, therefore, prone to developing pressure sores and pododermatitis on wire mesh floors (cf., Fullerton and Gilliatt, 1967). They are distinctively quadrupedal animals who usually keep all four feet on the ground and, unlike most other rodents, do not show a bipedal orientation stance. Therefore, relatively little head room – approximately 20 cm – is required when keeping them in enclosures. There is no need for a cover because the animals are poor climbers and will normally make no serious attempts to escape over walls that are only 30 cm high (Reinhardt, 1971).
"Rodents appear to
prefer sheltered areas of the cage, especially if those areas
have decreased light and height. Providing such a confined space
within a cage might be one way to enrich the environment of rodents"
(National Research Council, 1996, p. 48). The provision of such
protected, safe space is a basic requirement to assure data collection
of animals who are not unduly stressed by their living environment.
Guinea-pigs instinctively avoid open surfaces that expose them
full-view to potential predators. They will always keep close
to walls and shun the empty, unprotected central area of an enclosure
(White et al., 1989). To conclude from this that "social
groups of rodents do not use all the available space recommended
in current guidelines and probably do not require it for well-being"
(National Research Council, 1996, pp. 48) is a misleading generalization
that could be twisted in such a way that the animals are granted
only the bare minimum space without option to move around at all.
"All who care for or use animals in research, teaching, or testing must assume responsibility for their well-being. ... A good management program provides the environment, housing, and care that ... minimizes variations that can affect research results" (National Research Council, 1996a, pp. 1 & 21) and hence, reduces the number of research subjects needed to achieve statistically significant results. In the United States approximately 500,000 guinea-pigs were used in research during the year 2000 (United States Department of Agriculture, 2000).
Guinea-pigs need the social environment to guarantee their behavioral health, safeguard their physiological well-being (Sachser and Lick, 1991; Fenske, 1992), and assist them to cope with circumstances of confinement (Canadian Council on Animal Care, 1993). Compatible group-housing should, therefore, be the standard arrangement for them in the research laboratory (cf., Brain et al., 1994; European Council, 2000a; Figure 2).
Animals living in groups should be provided a floor area of no less than 1200 cm2 per breeding female, and no less then 750 cm2 per weaned, non-breeding animal. A box with an access hole makes the central area of the enclosure a place of refuge for the animals thereby improving their well-being and, at the same time, increasing the usable floor space (Figure 2). Such a refuge is an attractive location to sleep together and for pregnant females to give birth. Provisioning the box with a sliding door is an elegant way of facilitating the capture of the animals for cage cleaning: The whole group is trapped in the box, which is then simply lifted out of the pen during the cleaning procedure. A removable top of the box allows the capture of individual animals (Gray, 1988).
To minimize social tensions
arising from the presence of several mature males, and from overcrowding
it is recommended to keep only one mature male with 3-6 females
and remove the naturally weaned young at the age of three weeks.
The adolescents can then be housed in same-sex groups without
risk provided that male groups have no visual and no olfactory
contact with female groups. The mere exposure to the smell of
female urine will turn even the most compatible males into fractious
enemies who will no longer tolerate each other's presence (Reinhardt,
1971). Exchanging the mature breeding male of a group with another
male constitutes no problem. The females will accept him and there
will be no overt aggression. Strange females can be introduced
into an existing group without causing social turmoil (Raje and
Stewart, 2000) as long as none of the animals is nursing. When
they lactate, females do not tolerate strange females (Reinhardt,
1971). It is, therefore, good advice to introduce females into
an existing group only when none of the animals is lactating.
An individual animal who has been removed from a group can be
re-introduced without triggering xenophobic aggression provided
that he or she has not been scent-marked by another conspecific.
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If a medical condition requires temporary single-caging, the floor area should be no less than 35 x 35 cm [1225 cm2] in order to provide the space needed for an adult animal to stretch and turn around freely, and for a young animal to engage in locomotor play activities. If a research protocol requires temporary single-caging the floor space must be doubled [35 x 70 cm; 2450 cm2] to allow the placement of a covered refuge area, such as a hiding box. Singly caged guinea-pigs must never be kept isolated, but provision must be made that they have visual, auditory and olfactory contact with others of their own kind (cf., Fenske, 1992; Canadian Council on Animal Care, 1993).
Multiple-tier caging systems are not recommended because the shade cast from upper tiers on lower tiers makes it impossible to assure that "lighting shall provide uniformly distributed illumination" (United States Department of Agriculture, 1995a, p. 53; cf., Bellhorn, 1980; Clough, 1982). Uniform lighting for all animals, however, is a fundamental condition of scientifically valid research methodology (American Medical Association, 1992) assuring that no more than the minimum number of guinea-pigs are used to obtain statistically significant research results.
Guinea-pigs do well on a
commercial pelleted diet supplemented daily with fresh produce
and hay. "When good quality hay is supplied the consumption
of the more expensive pelleted diet is reduced and, by their vocalization
when they realize that the hay is about to be replenished, the
animals clearly indicate the great pleasure they obtain from eating
it and burrowing in it" (Sutherland and Festing, 1997, p.
401). Guinea-pigs must engage in regular gnawing behavior to prevent
overgrowth of their front teeth. Hard food pellets, carrots and
softwood sticks (Scharman, 1991) are suitable to meet this need.
Regular distribution of food treats, such as fresh, leafy produce
(Figure 3) and gentle handling help guinea-pigs to overcome
their fear of personnel. They should be picked up gently with
both hands, one firmly around the shoulder and the other supporting
the hindquarters. "Animal care staff are expected, at all
times, to have a caring and respectful attitude towards animals
in their care, and to be proficient in their handling" (Council
of Europe, 2000b, p. 27). Proper handling depends on the investigator
rather than on the subject. "Investigators should [always]
consider that procedures that cause pain or distress in human
beings may cause pain or distress in other animals" (American
Association for Laboratory Animal Science, 1997, p. 51). Nervous,
impatient or even callous investigators startle and distress guinea-pigs,
rendering research data collected from such animals virtually
useless. Guinea-pigs should be handled "as expeditiously
and carefully as possible in a manner that does not cause trauma,
overheating, ... behavioral stress, ... or unnecessary discomfort"
(United States Department of Agriculture, 1995a, pp. 21-22).
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The rooms in which guinea-pigs
are housed have to be quiet to avoid stress responses triggered
by intense and/or chronic noise (cf., Anthony and Harclerode,
1959).
With the exception of specific short-term experimental protocols,
guinea-pigs should always be kept on solid floor with bedding
(cf., National Research Council, 1996a). “When grid or perforated
floors are used, a solid resting area must be provided” (European
Council, 2000a, p. 5) that is sufficiently large to allow all
animals to lie on it simultaneously. Bedding of dust-free shavings
from seasoned soft wood, supplemented daily with high-quality
hay should be regarded as a basic form of environmental and feeding
enrichment (Figure 2). Regularly - at least twice a week - changed
bedding is the best guarantee of a hygienic cage environment.
To make the quarters for guinea-pigs in research institutions ‘comfortable’ the following provisions are recommended:
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Viktor Reinhardt is Laboratory Animal Advisor to the Animal Welfare Institute in Washington, DC. He is a clinical veterinarian and ethologist. He studied the social behavior and social roles of captive guinea pigs for his doctoral dissertation.