The general signs of a vitamin B12 deficiency in most animal species are a loss of appetite, variable feed intake and a dramatic growth suppression. In addition, sometimes there is rough skin and hair coat, vomiting and diarrhea, voice failure, and a slight anemia (Catron et al., 1952). Clinical cases in dogs and cats proven to be due solely to vitamin B12 deficiency have been limited. The megaloblastic anemia and the neurological symptoms observed in vitamin B12 deficiency in pernicious anemia in humans have not been observed in most other animals, including dogs and cats.
A positive diagnosis of vitamin B12 deficiency is usually made by the finding of subnormal serum and tissue B12 concentrations. Low serum levels are associated with low body content of the vitamin. In addition to serum vitamin B12, elevations of methylmalonic acid and total homocysteine are very sensitive and specific in diagnosing vitamin B12 deficiency and can be used to help differentiate vitamin B12 deficiency from folic acid deficiency (Stabler et al., 1996). Serum concentrations of vitamin B12 have been determined in dogs (Caprelli et al., 1994; Davenport et al., 1994) and cats (Dunn et al., 1984) to evaluate status of the vitamin. Vitamin B12 deficiency has been confirmed by elevated urinary methylmalonic acid in dogs (Williams et al., 1969; Chanarin et al., 1973) and cats (Vaden et al., 1992). A clinical test for vitamin B12 deficiency in dogs is to load the animal with a precursor of methylmalonic acid (e.g., valine) and measure urinary excretion of methylmalonic acid (Williams et al., 1969; Chanarin et al., 1973).
