The guinea pig does not have the microsomal enzyme L-gulonolactone oxidase, which catalyses the conversion of D-glucose into ascorbic acid or vitamin C. Vitamin C is involved in the synthesis of collagen and in the metabolism of cholesterol, carbohydrates and amino acids; its deficiency leads to breakdown of collagen and essential intercellular material. The guinea pig’s daily requirement of vitamin C is 10-30 mg/kg. Conditions such as pregnancy, lactation, growth, stress and concomitant diseases increase the needs.
Food pellets for guinea pigs contain vitamin C supplements, but this vitamin is extremely labile and is readily broken down, particularly if exposed to light, heat or humidity; even in optimal storage conditions, it disappears in about 3 months. For this reason, even guinea pigs fed with an apparently adequate bran can develop scurvy if the vitamin C content is insufficient or completely absent; it is, therefore, important to ensure an adequate daily supply through fresh food. Foodstuffs rich in vitamin C include cabbage, kale and citrus fruits. A cup of cabbage contains about 60 mg of vitamin C and 100 g of kale contains about 125 mg. The daily vitamin C requirement of a guinea pig can be provided by half a cup of these vegetables or a quarter of an orange. Attention should, however, be given not to provide excessive amounts of Brassicaceae, since these vegetables contain high levels of oxalates (which can cause the formation of urinary stones) and substances potentially able to cause goitre. Apples, carrots and lettuce do not contain much vitamin C.
Vitamin C can also be supplied in the drinking water at a dose of about 0.5-1 g/l; the drinking water should be changed at least once a day. Direct administration into the mouth with a pipette or dropper is, however, preferable; the product should be diluted in a small amount of water or fruit juice, at a dose of 10-30 mg/kg. Dietary supplementation with multivitamin products is not advised because such products could cause an overdose of the other vitamins.
Guinea pigs fed with a diet containing absolutely no vitamin C show clinical signs of the deficiency within 2 weeks. The symptoms include anorexia, swollen, tender joints, reluctance to move, altered development of bones and teeth, spontaneous bleeding from the gums and muscles and dishevelled fur. Death occurs within 3-4 weeks from emaciation, haemorrhages or secondary infections. However, a chronic form of deficiency is more likely in pet guinea pigs, with poorly specific signs: reluctance to move, limping, diarrhoea and altered appetite.
Treatment consists of parenteral administration of 25-50 mg/kg of vitamin C, parenteral administration of fluids, forced feeding and, possibly, antibiotics. Following this, the vitamin C is given orally and the diet is corrected. Clinical recovery usually takes 1 week. However, bone and joint lesions in growing animals may leave permanent deformations.
The incidence of vitamin C deficiency is probably greatly underestimated; furthermore, this condition may facilitate or accompany other disorders, so vitamin C supplementation is recommended for all sick guinea pigs.