Guinea pigs

Guinea pig use in laboratories dates back to the 17th century and they were widely used in research until the late 20th century, predominantly as models of disease, immune dysfunction and for drug safety testing (Guerrini 2003; Reid 1959). Over the past two decades, guinea pig research has dropped greatly, with 22,740 (0.6%) of licenced research procedures in the UK using guinea pigs in 2017 (Home Office 2018).

Social Behaviour

Guinea pigs are highly social animals, forming close-knit groups in the wild and in captivity, making social housing essential for their welfare (Pritchett-Corning 2015). Guinea pigs display low levels of aggression in comparison to other laboratory rodents. However, boars (male guinea pigs) will become highly aggressive towards one another when kept in visual or olfactory contact with sows (females) (Berryman 1978). As such, separation into same sex groups at the weaning age of roughly three weeks is recommended (Kaiser 2010).

Breeding groups should consist of one boar co-housed with one or more sows. Breeding males can be replaced by another boar without risk of aggression from the sows. Guinea pigs have an acute sense of smell and exposure to the scent of sow urine will provoke aggression between boars. Care should be taken to remove scent from clothing when working between enclosures, or groups of boars should be tended to before sows (Pritchett-Corning 2015). Additionally, suckling sows may become aggressive towards unknown sows that enter their enclosure. New females should not be introduced to a group when there are lactating females or suckling young present (Raje & Stewart 2000).

Housing

Enclosure sizes

Minimum enclosure sizes for guinea pigs in EU research establishments are detailed in Table 1.5 of Annex VII to Directive 2010/63/EU. An adult animal over 700g in weight should be provided a minimum enclosure floor space of 2500cm2 and enclosure height of 23cm, with groups sizes greater than two being provided an additional 900cm2 of space per animal. Note that adult guinea pigs grow to roughly 30cm in length and require a minimum of 3cm additional horizontal space to perform their species characteristic stretching posture.

Lighting

Guinea pigs are a diurnal species typically most active in early morning and evening, though this activity will change in line with the feeding and cleaning routines of the animal unit they are housed in. Lighting in guinea pig enclosures should be soft to simulate these times of day and follow a 12-hour day-night cycle.

Temperature

Guinea pigs do not dissipate heat well, making them sensitive to heat stroke (Pritchett-Corning 2015). They should be housed within a temperature range of 15-21°C (Home Office 2014), preferably in an open floor pen to allow for good ventilation. Due to their relatively large size and weight (adult animals can reach weights in excess of 1kg), guinea pigs can develop pressure sores and pododermatitis (inflammation of the skin of the feet) if housed in cages with wire or mesh floors (Fullerton and Gilliatt 1967). It is recommended that all animals are housed in enclosures with solid floors, covered with a layer of dust-free substrate such as wood chip or fleece.

Structuring enclosures

Guinea pigs are sensitive to the presence of unfamiliar or unseen persons in their vicinity (White et al. 1989). To reduce stress, cages or pen walls should be made from a material that allows good visual contact with the surrounding environment (e.g. wire mesh or transparent plastic). Guinea pigs will recognise handlers and actively seek to interact with them (Bradley 2001).

Guinea pigs avoid open surfaces and housing them in an unsheltered environment will increase stress (White et al. 1989). Guinea pig enclosures should contain at least one sheltered area large enough to hold all animals within the group. Ideally a pen will contain multiple shelters to allow the opportunity for animals to hide or isolate themselves from other members of their group. Guinea pigs do not create burrows in the wild. However, hay should be added to an enclosure, to allow animals to actively utilise it both for burrowing and as a supplement to their usual diet (Kaiser 2010).

Summary of the key features of guinea pig housing

Guinea pig enclosures must:

  1. Be large enough to provide enough space for exercise and normal social behaviour – see Table 1.5 of Annex VII to Directive 2010/63/EU.
  1. Be designed with a minimum height of 23cm.
  1. Be well ventilated with sides that permit observation of the out-of-pen environment.
  1. Have solid floors covered with an adequate depth of an appropriate substrate (such as wood chip) for hygiene, comfort and to permit foraging.
  1. Contain sheltered areas for resting, security and managing social interactions.
  1. Be softly lit and subject to a light-dark cycle.
  1. Kept at a temperature range of 15-21°C.

Environmental enrichment

The most important environmental enrichment for guinea pigs is being part of a social group. As a minimum, animals should be pair-housed and without exceptional justification, single housing of animals should not be permitted. If single housing is found to be necessary, the animal should remain within visual and olfactory contact with its cage mates and the period of isolation kept to an absolute minimum.

Guinea pigs are notably neophobic (fearful of novelty) and may stop eating as a response to the stress of new foods or structures in their enclosure. While it is important that these animals be provided with a diverse home environment, introducing new enrichments should be carried out carefully, gradually and with particular attention to the responses of the animals (Pritchett-Corning 2015).

Unless there is justification to the contrary, diets should be supplemented with fresh fruit and vegetables such as carrots or lettuce as a form of enrichment and, if given by hand, to help foster a positive animal-handler relationship. Guinea pigs are unable to synthesise vitamin C in sufficient quantity to meet their nutritional requirements, and provision of fruit or vegetables is a simple way to meet this need (Home Office 2014). Note that maintaining a consistent food selection from a young age is recommended as guinea pigs will typically refuse to eat unfamiliar food items (Kaiser 2010). Guinea pigs may respond to appearance of a favoured food item (or handler) with behaviours such as a high pitched ‘weeking’ vocalisation or a quick jumping motion referred to as ‘popcorning’. Both behaviours are associated with low anxiety and positive affect (mood) in guinea pigs and should be considered an indicator of good housing and husbandry (Bradley 2001).

Hay is a particularly important form of food enrichment for guinea pigs, supplementing their usual diet and encouraging natural foraging and grazing behaviours. Lack of forage material may result in stereotypies such as trichophagia (compulsive eating of hair) and as such hay should not be withheld without scientific justification (Gerold et al. 1997). The hay utilised should be of good quality and soft enough to prevent risk of eye damage to the animals.

Guinea pigs’ front teeth continue to grow throughout their lifetime. Provision of hard items to chew on is essential to preventing overgrowth. A hard-pelleted diet should be considered a minimum requirement to maintain tooth length, with preferable inclusion of wood blocks or chew sticks from a young age (Kaiser 2010).

Summary of environmental enrichment options for guinea pigs

Guinea pigs:

  1. Must be socially housed and should be kept either in single sex groups or in stable breeding colonies.
  1. Require objects to gnaw on (e.g. soft wood blocks, hard pellets, cardboard tubes) to prevent their teeth overgrowing.
  1. Require soft hay for burrowing, as a supplement to their usual diet and to allow enactment of natural foraging behaviour.
  1. Should have their standard pelleted diet supplemented with fresh fruit and vegetables as a form of enrichment and a source of vitamin C.

Recommended resources

Donnelly M (2015). Guinea pigs. In: Comfortable Quarters for Laboratory Animals (Eds. Liss C, Litwak K, Tilford D, Reinhardt V), Animal Welfare Institute.
Kaiser S (2010). The Guinea Pig. In: The UFAW Handbook on the Care and Management of Laboratory and Other Research Animals (Ed. Kirkwood RHJ), Wiley-Blackwell.

References

Berryman JC (1978). Social behaviour in a colony of domestic guinea pigs: Aggression and dominance. Zeitschrift für Tierpsychologie, 46(2), 200-214. doi:10.1111/j.1439-0310.1978.tb01445.x

Bradley TA (2001). Normal behavior and the clinical implications of abnormal behavior in guinea pigs. Veterinary Clinics of North America: Exotic Animal Practice, 4(3), 681-696. doi:10.1016/S1094-9194(17)30031-2

Fullerton PM, Gilliatt RW (1967). Pressure neuropathy in the hind foot of the guinea-pig. Journal of Neurology, Neurosurgery, and Psychiatry, 30(1), 18. doi:10.1136/jnnp.30.1.18

Gerold S et al. (1997). Influence of feeding hay on the alopecia of breeding guinea pigs. Journal of Veterinary Medicine Series A, 44(1‐10), 341-348. doi:10.1111/j.1439-0442.1997.tb01118.x

Guerrini A (2003). Experimenting with humans and animals: from Galen to animal rights, JHU Press.

Home Office (2014). Code of Practice for the Housing and Care of Animals Bred, Supplied or Used for Scientific Purposes, Williams Lea Group London.

Home Office (2018). Annual Statistics of Scientific Procedures on Living Animals Great Britain 2017, APS Group.

Kaiser S (2010). The Guinea Pig. In: The UFAW Handbook on the Care and Management of Laboratory and Other Research Animals (Ed. Kirkwood RHJ), Wiley-Blackwell.

Raje SS, Stewart K (2000). Group housing female guinea pigs. Lab Animal, 29(8), 31-32. Available at https://www.researchgate.net/publication/11958131_Group_housing_female_guinea_pigs

Reid ME (1959). The guinea pig in research. Academic Medicine, 34(1), 74. Available at https://journals.lww.com/academicmedicine/Citation/1959/01000/The_Guinea_Pig_in_Research.32.aspx

White WJ, Balk MW, Lang CM (1989). Use of cage space by guinea pigs. Laboratory Animals, 23(3), 208-214. doi:10.1258/002367789780810617