Guinea pigs are social animals, so they should always have a companion of their own species. Never pair a guinea pig with a rabbit – it’s dangerous for the guinea pig who may be bullied or catch a lung infection from the rabbit (Mancinelli & Bament 2014). Male guinea pigs that grow up in a mixed sex colony have social skills and fit in easily to a group: those that been brought up by just a mother or a mother and father are usually more aggressive to other males (Sachser et al., 2013). Adopt two or more guinea pigs: don’t buy one – that way you can get a bonded group.
So most guinea pigs can adapt either to large or to small groups, but the group needs to be a stable one. Keeping them together in a familiar group, or in the company of a bonded friend, reduces their stress (Kaiser et al., 2010). Like humans, they can get very distressed if they are parted from their friends. The regions of the brain that register this distress are very similar to humans (McMillan 2005). Ill or injured guinea pigs should not be isolated: put them with a friend and make all vet visits with that friend.
Male guinea pigs that are not brought up in a colony have trouble relating to other animals later in life while female guinea pigs are more adaptable whatever their social background (Kaiser et al., 2010). You can keep two female guinea pigs together, or a female with a neutered male (castrating males is straight forward). Two brothers that have been brought up together will usually also live in harmony or two unrelated males that are put together within a few days of birth. Adult males in larger all-male groups usually fight. Keeping mixed sex groups is not practical, as you will soon have a population explosion unless you neuter the males!
The other way you can get males to live together is to introduce a baby male guinea pig to an adult after it is weaned, for an adult male usually has no problem accepting a youngster of about eight to ten week of age. He may chase it for a bit for he will catch the scent of its mother but this will soon stop. Make sure there are places for the little one to retreat to – small enough so the adult cannot get in.
Don’t just put the new animal in with an existing guinea pig. The resident animal will fight to defend its territory. Adopt your new guinea pig from a rescue shelter and ask them to handle the introduction before you take the new animal home. Or you can introduce them on neutral territory, which does not belong to either of them.
Take time with the introduction. First mix their individual body scents. Take a clean hankie and wipe it over each piggy so that each individual takes on some of the scent of the other. Swap bedding daily. If you can, get a new run which will act as neutral territory, or try introducing them in the bathroom (not the slippery bath) or a kitchen.
When the two animals are newly together, make sure each animal can retreat into something like a cardboard box or a drainage tunnel from a builders merchant. What is needed are two hidey holes small enough for just one guinea pig – so that both can have their own space (Nordlund, 2004). Putting in just one larger box, and you may find that one guinea pig just monopolizes it. Sometimes it is useful to provide hidey holes with multiple openings so that it is impossible for either of the guinea pigs to be trapped inside by the other.
The introduction must be supervised at all times until there is no unrest. If there is serious fighting with blood, then the animals must be separated. Sometimes if a guinea pig has lived alone for a long time it will not accept a companion (McBride 2011). There is a longer more detailed article about this topic here.
Kaiser, S., Kruger, C. & Sachser, N, (2010), ‘The Guinea Pig,’ in eds Hubrecht & Kirkwood, J., The UFAW Handbook on Care and Management of Laboratory and other Research Animals, Eight Edition, Wiley-Blackwell, Chichester, UK, 381-398
McBride, A., (2011), Guinea Pigs. Understanding and caring for your pet, Magnet & Steel.
McMillan, F. D. (2005), Mental Health and Well-Being in Animals, Oxford, UK, Blackwells, 68.
Mancinelli, E. & Bament, W., (2014), ‘Chinchillas, guinea pigs, and degus: what vets need to know’, Veterinary Times. Available at http://www.vetsonline.com/publications/veterinary-times/archives/n-44-08/chinchillas-guinea-pigs-and-degus-what-vets-need-to-know.html Downloaded November 10, 2014.
Norlund, A., (2004), ‘Does the design of the shelter influence the levels of behavioural stress and aggression in group housed guinea pigs,’ Student Report 27, Skara, Sweden, Swedish University of Agricultural Sciences.
Sachser, N., Kaiser, S.,& Hennessy, M. B., (2013), ‘Behavioural profiles are shaped by social experience: when, how and why,’ Philosophical Transactions of the Royal Society, 368, 1-11.