Guinea pigs are far removed from their wild ancestors—similar to how dogs have evolved away from their wolf ancestors. As a member of discussion groups for veterinarians treating exotic pets, I often come across the abbreviation, “GP.” My first impulse is to wonder why, for instance, a general practitioner should have an ailing part of their anatomy—usually close to the tail or thereabouts—soaked in chlorhexidine solution. Then I quickly remember that not all GPs are humans. Non-exotics colleagues who have opened their practices and their hearts to rabbits, invariably see another beloved species piggybacked onto the long-eared one: guinea pigs, often informally abbreviated to GP. Guinea pig basics Like rabbits, guinea pigs are popular pets that have been overlooked by the mainstream veterinary curriculum. Although domestic guinea pigs are the result of selective breeding for the purpose of meat production, in Western culture we do not tend to think of them as food animals. While guinea pig owners do not have to listen to compulsive jokes about stew, both guinea pigs and rabbits are traditionally associated with experiments, and are still widely used in medical research. In this role, guinea pigs have contributed to the discovery of vitamin C, the tuberculosis bacterium, and the development of the vaccine against tuberculosis and asthma medications.1 Their respiratory system is one of their weakest links, while the mechanisms of their immune defenses are similar to humans. To their owners, guinea pigs are adorable little animals with a mischievous and playful side, and with a whole lot to say to each other and the world in general. The various noises they make have been described as “bubbling,” “rumbling,” “whistling,” and, less commonly, as “someone aggressively cleaning windows.” For all their cuteness and pleasant nature, guinea pigs are definitely not pushovers. They express their alarm and discontent by loud vocalization and by “tusking:” nipping with their incisors, much like other rodents and rabbits. Although they are social animals, they cannot be forced on each other, and require time and a stress-free environment to develop bonds. To veterinarians, guinea pigs present a cornucopia of illnesses, from common ones, like respiratory infections, pododermatitis, dental disease, skin issues, uroliths, and ovarian cysts, to more unusual ones, like pituitary-dependent hyperadrenocorticism and cholangiohepatitis, hyperthyroidism, gastric dilatation with volvulus, and even mesenteric torsion. An unexpected (to me) and perhaps counterintuitive feature of this species is if a female guinea pig is to be bred, this must take place before she is seven to eight months of age in order to prevent dystocia. During the last week of pregnancy, the hormone relaxin causes disintegration of the fibrocartilage of the pubic symphysis, literally opening a lifelong window for normal parturition. If the animal is bred for the first time, purposefully or accidentally, after seven or eight months of age, her pelvic symphysis will have already fused, and she will not be able to deliver the fetuses naturally, but only by C-section.2 The guinea pig’s distant cousin, the peaceful and dignified capybara, is known for getting along with just about any other animal, including predators. Guinea pigs are similarly agreeable, but far more vulnerable to attack from predators due to their small size and fast movements. It is never a good idea to leave them unattended with dogs or cats, no matter how well these animals might get along in the presence of humans. Moreover, out of the common house pets, guinea pigs are the most susceptible to catching infections from other species. Bordetella bronchiseptica is a pathogen carried by rabbits and dogs that are often asymptomatic, but can infect guinea pigs, resulting in bronchopneumonia. It is never recommended to keep guinea pigs together with rabbits, the only exception being animals that have already bonded and would be stressed by a separation. Health While many guinea pigs live healthy long lives (up to nine years), others are afflicted with chronic ailments resulting from neglect, and persisting even after they are rehomed into excellent living conditions. Then there are those that suffer from imperfect health through no fault of the owner. One might wonder how an animal so robust in its severe natural habitat of the Andes is prone to so many health problems when living in the safety and plenty of people’s homes. The main reason is simply they are not the same animal any more. The domestic guinea pig, Cavia aperea f. porcellus, is as distinct from its wild ancestor as dogs are from wolves. Like all domestic species, it is neither represented in the wild, nor fit to survive without human care and protection. There is no consensus as to which species of present-day wild cavy was the ancestor of the domestic guinea pig. The process of domestication of wild guinea pigs started, according to some archeologists, as early as 7,000 years ago.3 The animals were selectively bred for their meat, resulting in profound changes over time. Wild cavies are more streamlined, lean, and nimble; their ears and feet are smaller and their snouts longer. The wild prototype of domestic guinea pigs has a robust musculoskeletal system, while the bones of domestic cavies are more fragile and brittle, making them prone to diseases such as osteodystrophy, which often result from calcium-phosphorus imbalance in their diet, even with adequate levels of vitamin C. Those little feet Many of us have seen the slow-motion video of a herd of house guinea pigs following their human owner in a stampede over carpets separated by a strip of bare floor, taking off and leaping over this gap with a lightness surprising in such stocky and short-legged animals. Whatever the reason for the animals’ avoidance of the bare floor, to me, this video symbolizes the fragility of guinea pigs’ feet. In my experience, pododermatitis, or bumblefoot, is the second most common presenting complaint in guinea pigs after respiratory illness. I have often wondered why this might be, seeing as guinea pigs’ feet actually have more cushioning structures4 than those of other rodents that are not prone to pododermatitis. Perhaps there is a correlation between the presence of a large dome of hyaline cartilage, which is resistant to compression in the posterior pad of the forepaw, and the susceptibility of this particular location to pododermatitis. Studies showed the forepaw pad did not deform much against the floor during locomotion,5 suggesting the skin over this pad cannot retreat from the impact of harsh surfaces, such as wire cage floors or sharp bedding substrate. Once the skin is broken and makes contact with soiled bedding or flooring, inflammation and infection set in fast. It is most commonly caused by Staphylococcus aureus, but can also be fungal. The condition often becomes chronic, with periods of calm in between flare-ups. If infection is not treated immediately and decisively, it can spread to the tendons and ligaments and even bone, leading to osteomyelitis and deformity in the entire foot. Pain control is essential, with doses of metacam for guinea pigs being even higher than for rabbits: 1.5 mg/kg twice daily. In advanced and severe cases, limb amputation, unfortunately, is the only solution to ongoing pain and inflammation. Scabs form over ulcerated areas of the feet, and it is not always clear whether a given scab is preventing a festering infection from draining, or protecting an area that has gone quiescent. Since one of the procedures for treating pododermatitis is soaking the feet in chlorhexedine solution, this in itself can help detach scabs that “don’t belong.” While the science of treating this condition has been described extensively,6 the art relies on the individual circumstances and temperament of the patient. Some guinea pigs do well with bandages and all manner of improvised padding, while others will not tolerate anything attached to their feet. This part of their bodies keeps a record of how well they were or are cared for, and how clean is their environment. Veronica Gventsadze, MA, PhD, DVM, worked as a conference interpreter and a university professor of the humanities before gathering the courage to turn her love of science and animals into a profession. Upon graduating from Ontario Veterinary College (OVC) in 2008, she settled in British Columbia where she works in small animal private practice. Dr. Gventsadze writes fiction incorporating lessons learned from animals. She can be reached through her website https://veronica-gventsadze.com/contact. References https://www.understandinganimal research.org.uk/animals/a-z-animals/guinea-pig/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7150066/ https://www.nature.com/articles/s41598-020-65784-6 https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24271 https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24271 https://www.veterinary-practice.com/ article/guinea-pig-pododermatitis-bumblefoot-sore-hocks
