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SMALL mammals such as rabbits and rodents constitute a small, but nonetheless significant, part of veterinary practice, and are valued pets and show animals in many households. In Europe, figures collected by the pet food industry indicate that there are 21.25 million small mammals, including guinea pigs, kept as pets in the European Union, which is about 10 per cent of the pet population (FEDIAF 2012). In the UK, an estimated 0.7 million pet guinea pigs make up 1 per cent of the pet population (PFMA 2015) and 1.36 million are kept as pets in the USA (AVMA 2012).
Guinea pigs can make challenging patients; they are adept at masking signs of disease and are extremely sensitive to the effects of stress and pain, often becoming depressed and refusing to eat when hospitalised (Fawcett 2011, Quesenberry and others 2012). Many veterinary practitioners will have received minimal training in guinea pig medicine and surgery and may feel lacking in knowledge, confidence, and expertise when faced with this species. As guinea pigs do not require routine veterinary visits for vaccination, preventive medicine including routine neutering and regular health checks are far less widely employed than in other companion animals such as dogs, cats and rabbits, and some owners will be reluctant to spend much money on treating what they may perceive as a ‘cheap’ pet. The old adage that ‘common things are common’ and an appreciation of the conditions likely to be encountered can therefore provide valuable guidance for clinical examinations and diagnostic investigations.
Poor husbandry and diet are recognised as a leading cause of morbidity and mortality in guinea pigs (Fawcett 2011). Most veterinarians and many owners will be aware that guinea pigs are unusual among companion animals in requiring exogenous vitamin C, but the importance of other aspects of diet, such as fibre, calcium, phosphorus and vitamin D levels, and the benefits of neutering, are less widely appreciated. However, accurate husbandry and dietary advice, and awareness-raising campaigns about guinea pig welfare, are now widely available via the internet from charities such as the BVA's Animal Welfare Foundation, RSPCA and PDSA, and specific groups such as the British Cavy Council for breeding and show animals.
Better basic husbandry information, along with developments and improvements in commercial diets can be demonstrated to contribute to improvements in small mammal health and welfare. Guinea pigs, like rabbits, have continually growing elodont teeth and require high fibre levels for gastrointestinal (GI) function; the commonly fed muesli-type diets are considered detrimental to their dental and GI health. In rabbits, improvements in commercial diets and information from recent studies highlighting the detrimental effects of traditional muesli-type diets (Prebble and others 2014, Meredith and others 2015) have contributed to a greater understanding and awareness of the role of diet in disease. In the UK, the PDSA, through its Animal Wellbeing reports, has found that since 2011 there have indeed been significant improvements in the diets fed to pet rabbits, with an estimated 300,000 fewer rabbits being fed muesli-type diets and 200,000 more rabbits being fed the recommended amount of hay (PDSA 2014). Similar research would be beneficial in guinea pigs.
It is encouraging, therefore, to see the increasing amount of interest, research and welfare focus on small companion animals other than cats and dogs over recent years. Many textbooks and journals, eg, the Journal of Exotic Pet Medicine from the Association of Exotic Mammal Veterinarians, provide education and a forum for the dissemination of information, the European College of Zoological Medicine has a recently developed a small mammal speciality, the American Board of Veterinary Practitioners offers board certification in exotic companion mammal practice, and, in addition to a growing number of specific exotics conferences, most small animal veterinary conferences now have a well-established and popular exotic animal stream.
Our understanding of some areas of small mammal medicine, such as rabbit medicine, has increased greatly in recent years, but guinea pigs have received less attention. Although diseases are quite well described in their laboratory counterparts, diseases of pet guinea pigs are relatively poorly documented and there have been only very few studies on types and prevalence of diseases encountered in practice. Textbook descriptions by experienced practitioners, individual case reports, small case series or prevalence studies of a particular condition make up the majority of published information.
A retrospective study from the Czech Republic by Minarikova and others (2015), summarised on p 200 of this issue of Veterinary Record, reviewed the disease prevalence in 1000 pet guinea pigs presenting to a single university exotic animal clinic over a five-and-a-half-year period, either as first opinion (82 per cent) or referral (18 per cent) cases. These included animals presented for routine health checks as well as for specific conditions, and overall only 8.1 per cent were free of disease. In addition to a full clinical examination, all 1000 guinea pigs had an oral examination using a paediatric laryngoscope and 30 per cent had blood samples taken, which probably reflects the specialist nature of the authors' clinic. A wide variety of conditions were diagnosed covering all body systems, although otitis media was the only condition documented that could be categorised as neurological disease. The authors also investigated the influence of age and sex on disease prevalence.
Dental disease was the most common condition, seen in 36.3 per cent of guinea pigs, and emphasises the need to include an intraoral examination as part of any clinical examination in this species. Acquired disease such as tooth elongation was the main finding, as expected, but this category also included iatrogenic damage due to clipping of teeth by other practitioners. As in rabbits, this practice is outdated, unnecessary and traumatic, and should not be used (Cope and other 2013). The authors highlight the need to avoid muesli-type diets and feed good quality hay, grass, vegetables and pellets for both dental health and to avoid GI conditions, such as GI stasis (seen in 8.4 per cent). Other recent studies have reported that dietary factors such as mineral (eg, calcium/phosphorus) imbalances or genetic factors, rather than dietary abrasiveness, are likely to be associated with the development of acquired dental disease in guinea pigs (Müller and others 2014). Optimum vitamin D levels are also recommended, and exposure of guinea pigs to UVB, which is shown to significantly increase serum 25-OHD3 levels in albino animals, may also be important (Watson and others 2014).
Skin diseases were the second most common disorder, seen in 33.1 per cent of guinea pigs, of which a third were due to sarcoptic mange (Trixacarus caviae). This, and the finding of several other ectoparasitic species (mites, lice, fleas), highlights the need for routine checks and ectoparasite control, particularly in groups of young guinea pigs at breeders or in pet shops.
Ovarian cystic disease is known to be common in guinea pigs and this was confirmed in this study, being seen in 21.9 per cent of the 456 female guinea pigs presented. Routine neutering of female guinea pigs is increasingly offered by veterinarians as a preventive measure and is recommended by the authors to prevent this and other reproductive disorders. Ovariectomy is a simpler and less invasive option than ovariohysterectomy and is to be encouraged.
Ophthalmological disease (15 per cent), including heterotropic calcification of the ciliary body and ‘fatty eye’ (seen almost exclusively in this rodent species), along with gastrointestinal disease (13.1 per cent), also featured highly.
The apparent impact of hypovitaminosis C was surprisingly low, with only three cases (0.03 per cent) suspected at postmortem examination. However, vitamin C levels were not measured in any guinea pig and details of dietary histories are not presented, and so the potential role of suboptimal levels cannot be fully assessed. On the basis of their findings, the authors do not recommend additional vitamin C supplementation in non-breeding guinea pigs, pointing out that high doses could be linked with osteoarthritis. While this suggests that standard diets are providing sufficient vitamin C to prevent overt signs of hypovitaminosis C, I would suggest that further studies are needed to assess the role that vitamin C levels play as a potential underlying or contributory factor in conditions such as dental, skin, and urinary tract diseases, seen so commonly in guinea pigs.
The documentation of the very wide variety of disease conditions seen in guinea pigs, and the finding that dental disease, ovarian cystic disease and scabies (sarcoptic mange) are the commonest, will probably come as small surprise to practitioners seeing guinea pigs as part of their case load and reflect their clinical experience – common things are indeed common, and most are preventable with good husbandry and routine neutering. The welfare implications of all these common diseases are significant: dental disease can cause severe oral pain, cystic ovarian disease frequently causes abdominal pain, and mange can cause intense pruritus and self-trauma, which can all lead to anorexia, metabolic and GI disturbances, and death. This study provides a valuable boost to our understanding of disease prevalence in this popular species. I hope it will help to direct and encourage further research in guinea pig medicine and help to emphasise the requirement for education and preventive interventions to improve guinea pig welfare.
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