Guinea pigs are naturally social and generally adapt well to the introduction of a new cage mate. Observe quarantine procedures, however, and be careful to keep only one male to a cage. Two males kept together in one cage may become territorial and will fight. Make the introduction when there is no other excitement. Try to set things up in advance in favor of the introduction by using a neutral or freshly cleaned and disinfected cage, with plenty of fresh bedding and some treats in different corners. Put both guinea pigs in at the same time and let them look for the treats. If they fight, remove the aggressor and leave the other one in the cage; try again a day later.
Companionship is very important to guinea pigs, since they often live in large groups in the wild. If you plan to keep just one guinea pig, you will need to give it extra love and attention to compensate for the absence of other guinea pigs.
Is routine important?
Guinea pigs appreciate, and respond positively to routines. Keeping a routine is especially important in the kind of food that you select, time of feeding, and handling schedules. If you suddenly change your behavior or their routine, they may grow uncomfortable or stressed. A routine forms the framework for their daily lives, so avoid making unnecessary changes, and when necessary, do it gradually. Your guinea pig will thank you for it.
Signs of stress
Guinea pigs can become stressed by sudden changes in water, food, or bedding. Guinea pigs display symptoms of stress in ways similar to other mammals. They become increasingly susceptible to disease, can become irritable and aggressive or the reverse, depressed and less active. They may also develop diarrhea and consequently lose weight, drink more water, and become listless. These may also be signs of an underlying illness. If your guinea pig is showing these signs and you are unable to pinpoint any recent changes in your pet's daily life that could have caused stress, it's best to seek a veterinarian's consultation. If you feel the signs are due to stress, remove the cause of stress, and consult your veterinarian if the signs are severe or continue for more than a day or two. Guinea pigs are generally hardy, but once they become ill, they are even more easily stressed. They do not handle clinical procedures or treatments well, so it is vitally important to keep your guniea pig in a good environment and on a proper diet to maintain his health.
Environmental enrichment (toys and exercise)
Appropriate toys for guinea pigs include seesaws, solid-floor ramps, run-about balls, thick-walled PVC pipe (also provides a good "hide" for your guinea pig - a definite must!), and just about anything they can explore. Guinea pigs are not particularly agile and do not climb well, but they love to chew and need to chew on hard substances such as wood to keep their teeth worn down. As with other rodents, their teeth continue to grow throughout their lives.