The fancy rat (Rattus norvegicus domestica) is the domesticated form of Rattus norvegicus, the brown rat, and the most common species of rat kept as a pet. The name fancy rat derives from the use of the adjective fancy for a hobby, also seen in "animal fancy", a hobby involving the appreciation, promotion, or breeding of pet or domestic animals. The offspring of wild-caught brown rats, having become docile after having been bred for many generations, fall under the fancy type.
Fancy rats were originally targets for blood sport in 18th- and 19th-century Europe. Later bred as pets, they now come in a wide variety of coat colors and patterns, and are bred and raised by several rat enthusiast groups around the world. They are sold by breeders and in pet stores, and they are also often available at animal shelters.
Fancy rats are quite independent, affectionate, loyal and easily trained. They are often considered more intelligent than other domesticated rodents. Healthy fancy rats typically live 2 to 3 years.
Fancy rats are used widely in medical research, as their physiology is similar to human physiology. When used in this field, they are referred to as laboratory rats (lab rats).
Domesticated rats are physiologically and psychologically different from their wild relatives and typically pose no more of a health risk than other common pets. For example, domesticated brown rats are not considered a disease threat, although exposure to wild rat populations could introduce pathogens like the bacteria Streptobacillus moniliformis into the home. Fancy rats have different health risks from their wild counterparts, and thus are unlikely to succumb to the same illnesses as wild rats.
History
The origin of the modern fancy rat begins with the rat-catchers of the 18th and 19th centuries who trapped rats throughout Europe. Rat-catchers would then either kill the rats, or, more likely, sell the rats to be used in blood sport. Rat-baiting was a popular sport until the beginning of the 20th century. It involved filling a pit with several rats and then placing bets on how long it would take a terrier to kill them all. It is believed that both rat-catchers and sportsmen began to keep certain, odd-colored rats during the height of the sport, eventually breeding them and then selling them as pets. The two men thought to have formed the basis of rat fancy are Jack Black, self-proclaimed rat-catcher to Queen Victoria, and Jimmy Shaw, manager of one of the largest sporting public houses in London. These two men are responsible for beginning many of the color varieties present today. Black, specifically, was known for taming the "prettier" rats of unusual color, decorating them with ribbons, and selling them as pets.
Rat fancy as a formal, organized hobby began when a woman named Mary Douglas asked for permission to bring her pet rats to an exhibition of the National Mouse Club at the Aylesbury Town Show in England on October 24, 1901. Her black-and-white hooded rat won "Best in Show" and ignited interest in the area. After Douglas' death in 1921, rat fancy soon began to fall back out of fashion. The original hobby formally lasted from 1912 to 1929 or 1931, as part of the National Mouse and Rat Club, at which point Rat was dropped from the name, returning it to the original National Mouse Club. The hobby was revived in 1976 with the formation of the English National Fancy Rat Society (NFRS).
Differences from wild rats
While domesticated rats are not removed enough from their wild counterparts to justify a distinct species (like the dog versus grey wolf), there are significant differences that set them apart: the most apparent is coloring. Random color mutations may occur in the wild, but these are rare. Most wild R. norvegicus are a dark brown color called "agouti," while fancy rats may be anything from white to cinnamon to blue.Refer to specific information in the Varieties section
Behaviorally, domesticated pet rats are tamer than those in the wild. They are more comfortable around humans and known to seek out their owners while roaming freely. They have decreased reactions to light and sound, are less cautious of new food, and have better tolerance to overcrowding. Domesticated rats are shown to mate earlier, more readily, and for a longer period of time over their lifespan. Also, domesticated rats exhibit different behaviors when fighting with each other: while wild rats almost always flee a lost battle, caged rats spend protracted amounts of time in a belly-up or boxing position. These behavioral traits are thought to be products of environment as opposed to genetics. However, it is also theorized that there are certain underlying biological reasons for why some members of a wild species are more receptive to domestication than others, and that these differences are then passed down to offspring (compare domesticated silver fox).
The body structure of domesticated rats differs from that of a wild rat as well. The body of a fancy rat is smaller, with larger ears and a longer tail. Domesticated rats have generally smaller and sharper facial features as well.
Domesticated rats have a longer lifespan than that of wild rats. Because domesticated rats are protected from predators and have ready access to food, water, shelter, and medical care, their average lifespan is around two to three years, in contrast to wild R. norvegicus, which average a lifespan of less than one year. However, wild rats generally have larger brains, hearts, livers, kidneys, and adrenal glands than laboratory rats.
The fancy rat and wild rat also largely face different health concerns; for example, fancy rats may be at risk of developing a pneumococcal infection from exposure to humans, while wild rats may harbor tapeworms after coming in contact with carriers such as cockroaches and fleas.
Health
While living indoors decreases the risk of contracting certain diseases, living in close quarters with other rats, lack of proper protection from environmental factors (e.g. temperature, humidity), an unhealthy diet, and the stresses inherently associated with living in an unnatural habitat can all adversely affect a rat's health to make them more prone to specific conditions.
Fancy rats' susceptibility to disease can thus be impacted by exposure; stress; living conditions, including rat companionship; and diet.
Accordingly, like other animals, a fancy rat's health may benefit from access to veterinary care, a well-balanced and rat-specific diet, proper living conditions, and adequate enrichment.
Common concerns
Excess porphyrin Porphyrin is a brown-red, mucus-like substance which may look like dried blood that fancy rats secrete around the eyes and nose. An excess amount of porphyrin, called chromodacryorrhea, generally indicates stress, injury, or illness (especially respiratory infections). It may also be caused by temporary irritation in the eye, such as an accidental scratch.
Respiratory disease Fancy rats often suffer from bacterial and/or viral respiratory infections, including murine respiratory mycoplasmosis (MRM, caused by Mycoplasma pulmonis), rat coronavirus (RCV, particularly the SDAV strain), and Sendai virus.
MRM, also known as "chronic respiratory disease" (CRD), is common among pet rats but very rare in laboratory rats, who are generally bred to be specific pathogen-free. The bacteria causing MRM among pet rats, Mycoplasma pulmonis, are transmitted via aerosol, direct contact, and in utero; thus, infection generally begins at birth and persists for the rat's life. Approximately 70% to 100% of pet rats test positive for Mycoplasma, though many won't display symptoms of MRM until they're older, if at all. Earlier MRM symptoms may include "snuffling," sneezing, and excess porphyrin. Advanced MRM symptoms include shortness of breath, crackling sounds while breathing, weight loss, hunched posture, and ruffled coat.
Neoplasia Fancy rats are predisposed to both benign and malignant (cancerous) neoplasms.
Fancy rats very frequently develop mammary gland tumors and pituitary gland tumors, especially if they are intact females and/or are fed high-calorie diets Female rats spayed at a young age are significantly less likely to develop mammary and pituitary tumors than intact females.
Most mammary tumors are benign (fibroadenomas); less than 10% are malignant (adenocarcinomas). As long as the rat is an acceptable anesthetic candidate, veterinarians generally consider the surgical removal of mammary tumors to be beneficial due to improved welfare. However, mammary tumors are known to frequently recur.
Pituitary tumors affect over 80% of some strains of laboratory rats older than 24 months. They are generally benign (adenomas) and cause neurological symptoms that worsen over time. One study found that pituitary tumors affected ~5% of female rats spayed between 5–7 months old versus ~74% of intact females.
Kidney disease Chronic progressive nephropathy (CPN) is a common renal disease in older rats, especially males.
Lesser concerns Mites are microscopic bloodsucking parasites that can irritate the skin of fancy rats, and if they have a preexisting health condition, it can cause them to die from their bodies' inability to handle two problems at once.
Rats may also develop ringtail if kept in areas with low humidity or high temperatures. Staphylococcus spp. are a mostly benign group of bacteria that commonly reside on the top of the skin, but cuts and scratches from social and hierarchical fighting can open up the pathways for them to cause ulcerative dermatitis.
Fancy rats generally avoid disease-causing bacteria such as Salmonella and Pseudomonas aeruginosa; the latter is absent in treated water. They may also more easily avoid vectors like cockroaches, beetles, and fleas which are essential for the spread of endemic typhus and intestinal parasites like the rat tapeworm.
Tyzzer's disease, protozoic infections (e.g. Giardia muris), and pseudotuberculosis are usually seen in stressed or young rats. Additionally, pet rats are exposed to Streptococcus pneumoniae, a zoonotic disease caught from humans, not the same bacteria associated with pneumonia. A human-associated fungus, Pneumocystis jirovecii (also found in almost all domesticated animals), is usually asymptomatic in the rat, unless the rat's immune system is compromised by illness. If this occurs, the infection can develop into pneumonia.
Veterinary care
Pet rats require access to veterinary care, preferably from veterinarians experienced in exotic animal or small mammal medicine. Not all general practice veterinarians are trained in rat medicine, so owners are often advised to seek specialists.
Common veterinary procedures for rats include:
Physical examinations and wellness checks Treatment of respiratory infections (the most common health issue in pet rats) Tumor removal surgery, particularly mammary tumors Dental care for overgrown or misaligned incisors Treatment of skin conditions and parasites Emergency care for injuries or acute illness
Anesthesia in rats requires specialized knowledge due to their small size and unique respiratory anatomy. Isoflurane gas anesthesia is commonly used for surgical procedures.
Early detection of illness is important, as rats often hide symptoms until disease is advanced. Owners should monitor for signs such as labored breathing, lethargy, weight loss, porphyrin discharge around the eyes or nose, or changes in behavior.
Zoonotic risks Keeping rats as pets can come with stigma that rats supposedly transmit dangerous diseases to their owners. Usually, rats bred as pets are tested and treated for diseases and parasites.
One fear may be that rats carry plague, but R. norvegicus is not among the list of species considered a threat in the Western US.