Rodents (for example, rats, Rattus norvegicus domestica; mice, Mus musculus domestica; gerbils, Meriones unguiculatus; and golden hamsters, Mesocricetus auratus) are well-known and popular companion species commonly seen in the pet trade. The prevalence of these species as laboratory models means that research into appropriate dietary composition and nutritional requirement is prevalent. However, there are still some common pathologies with a nutritional basis that can afflict companion rodent species. Obesity, poor coat condition, impacted cheek pouches, skeletal problems and poor faecal consistency can all affect pet rodents. An inappropriate diet or one with too much rich and “empty calorie” food is often the underlying or principal causal factor of these conditions.
Guinea pigs and the vitamin C problem
Perhaps the most well-known nutritional need in the rodent world is that of guinea pigs (Cavia porcellus) and vitamin C (ascorbic acid). Among rodents, guinea pigs have the unique requirement of the dietary inclusion of vitamin C (Ediger, 1976). Guinea pigs cannot synthesise vitamin C as they lack the enzyme (L-gulonolactone oxidase) that converts L-gulonolactone to L-ascorbic acid (Fawcett, 2011). As such, guinea pigs need a consistent supply of dietary vitamin C to prevent any illnesses associated with hypovitaminosis C.
Guinea pigs cannot synthesise vitamin C as they lack the enzyme (L-gulonolactone oxidase) that converts L-gulonolactone to L-ascorbic acid
The estimated number of pet guinea pigs in the UK is around 400,000 (Harrup and Rooney, 2020). However, in spite of this popularity, guinea pigs can mask signs of illness incredibly well, which can cause issues in the timing of veterinary intervention (Fawcett, 2011). Like many prey species, the evolutionary adaptations that preserve life when the animal is feeling “off colour” in the wild can result in premature death in captive conditions because they make it harder for owners to spot potential problems.
Prevention of dietary conditions in guinea pigs
It is important that owners have the nutritional needs of guinea pigs (Figure 1) explained to them. As such, veterinary surgeons should advise on the quality and quantity of foods provided as part of their daily husbandry. A “balanced diet” of correct, species-specific pellet with vegetables and quality forage (eg meadow hay, timothy hay and alfalfa) will keep a guinea pig healthy. Veterinary surgeons should also advise owners on how to store and maintain the quality of their pet’s feed. Any storage of pellets in warm conditions or direct sunlight will result in the breakdown of vitamin C. Natural loss also occurs over time, therefore pelleted feed that has been kept for longer will contain less vitamin C than those more recently manufactured. Although owners may provide vitamin C in the animal’s drinking water, this can be lost quickly due to exposure to sunlight.
The term “hypovitaminosis” refers to the condition caused by a dietary lack of a vitamin. In guinea pigs, an insufficient intake of vitamin C can cause “scurvy” or hypovitaminosis C, a condition with potentially serious effects.
A guinea pig suffering from hypovitaminosis C will present with:
- Poor hair-coat condition
- Swellings or sores in and around the mouth
- Abnormal tooth wear/growth
- Delayed wound healing
- Poor appetite and potential diarrhoea
- Lethargy and a reluctance/difficulty to move normally
- Joint swelling/enlargement
- Reduced fertility
Although these signs are generic and common to a range of conditions, the veterinary surgeon can make a differential diagnosis by asking for details of the husbandry and diet provided.
|Further information can be found in relevant BSAVA manuals (Keeble and Meredith, 2009; Meredith and Delaney, 2010).|
Hypovitaminosis C can be treated if caught early. Malocclusion will require future dental work to continually correct as the animal ages, and patients may require long-term analgesia for arthritis and afflicted joints. Veterinary surgeons should educate owners to spot signs of gut stasis and bloating, as these can be life-threatening and require urgent veterinary care. Good quality roughage will ensure that a guinea pig’s digestive tract continues to function normally and maintains its constant motility.
Veterinary surgeons should educate owners to spot signs of gut stasis and bloating, as these can be life-threatening and require urgent veterinary care
Just as hypovitaminosis can cause health problems, so can hypervitaminosis in guinea pigs, therefore it is important not to over-supplement with vitamin C. Bladder and renal stones, joint problems and increased prevalence of arthritis occur at levels of vitamin C above 100mg/kg. Although acceptable ranges vary, 10 to 20mg/kg of vitamin C per day per animal is recommended to keep a guinea pig healthy (Richardson, 2000).
Small amounts of fruit and root vegetables should be offered as these are high in sugar content but low in fibre. Higher amounts of leafy green vegetables are best, avoiding brassicas as they are high in calcium and can cause bloat or renal stones. Kale, spinach, turnip greens, parsley, romaine lettuce, dandelion leaves and chickweed (so long as the source is pesticide free) are good leafy green sources of vitamin C. Natural grazing is also to be encouraged, but grass clippings should be avoided as they can cause diarrhoea (Richardson, 2000).
Hypervitaminosis D and pelleted food
Guinea pigs have also been noted as susceptible to hypervitaminosis D when pelleted feed contains vitamin D content that is higher than expected (Jensen et al., 2013). In this study, the authors noted that this condition presents suddenly and unexpectedly and that affected guinea pigs respond poorly or not at all to supportive care. The authors also stated the importance of the close scrutiny of individual animals, even when normal conditions of husbandry and diet are or are assumed to be maintained, to check for untoward signs of poor health in the animals. Any unfortunate or unexplained change in feed consistency at the manufacturing stage can result in toxicity for the animal, and a keen eye from the owner can help save the animal’s life.