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Fancy rats (Rattus norvegicus domestica) are becoming increasingly frequent patients of veterinarians in Europe. Indeed, because of their gentle and intelligent nature, they make very good pets. Rats have been used in research for decades and literature provides a large choice of publications about the main laboratory rat strains. However, due to the highly selective breeding and unique husbandry conditions, their genetic background and their environment differ greatly from those of pet rats. Thus, it seems relevant to suppose that pet rats’ ailments might differ from those of laboratory rats. Currently, veterinary literature on pet rats is still scarce, with exotic small mammals medicine books focusing more on rabbits, guinea pigs, ferrets, and hamsters.

Hence, this study aimed to provide a classification of the main diseases in pet rats in France.

For this purpose, a retrospective study of more than 1000 rat patients was performed. Medical records of companion rats examined at a French Hospital and Reference Clinic between 2006 and 2021 were reviewed. Information regarding the age, sex, chief complaint of the owner and diagnosis of the veterinarian was extracted from each file and analyzed.

Major chief complaints in our total population included respiratory signs (35%), masses (21%), neurological signs (13%), and lameness (9%). Using the age and sex of the patients, chief complaint profiles could be established. Those profiles were displayed as a classification tree, allowing veterinarians to easily visualize the most likely chief complaints for a given age group and sex. Each profile was also further detailed and displayed as double level-pie charts using the most frequent veterinary diagnosis for each chief complaint. Through this process, three statistically relevant age groups emerged, offering a definition of aging in pet rats, not yet described to the best of the author’s knowledge. Pet rats can be considered young until 12 months old, senior until 24 months, and geriatric over 24 months.

In our population, respiratory signs were most often a manifestation of chronic respiratory disease (CRD) in all groups (over 60%). Masses were most often mammary gland tumors in senior and geriatric females (over 65%, 75% fibroadenoma) and abscesses in males (over 50%). Neurological signs were often under-investigated and mostly diagnosed as vestibular syndrome (over 55% in all groups). Pituitary gland tumors in senior and older rats were mostly suspected (14 to 65%). Lameness was overrepresented in geriatric male rats (22% vs 8% in geriatric females) and was mostly associated with polyradiculoneuropathy (59%).

The provided material is intended to be a useful pedagogic tool for both veterinarians and pet rat owners, which could be further complimented by providing illustrated clinical brochures of pet rats’ major diseases.