The Condition

Many pastures in the United Kingdom are deficient in cobalt, causing a deficiency in sheep grazing those pastures. Lambs, after weaning, are particularly susceptible to 'pine', exhibiting growth retardation, debility, emaciation and a watery discharge from the eyes (Suttle et al., 1991; Vellema et al., 1997). In severe cases there is a loss of appetite and anaemia. Resistance to diseases such as helminthiasis may also be impaired (Ferguson et al., 1989; MacPherson et al., 1989; Vellema et al., 1996). The livers of the lambs become pale, swollen and friable through the accumulation of lipids (ovine white liver disease) (Kennedy et al., 1994a; Kennedy et al., 1994b).

Adult ewes affected by cobalt deficiency may show secondary effects in the form of infertility and poor mothering ability, and there is evidence that cobalt deficiency in pregnant ewes reduces the viability of their offspring (Fisher and MacPherson, 1991; Fisher and MacPherson, 1992).

The only known biological role for cobalt is as a constituent of vitamin B₁₂, which has two major coenzyme functions in the body. Methylcobalamin promotes methionine synthesis. Methionine supply ultimately influences DNA synthesis (Kennedy et al., 1992; Kennedy et al., 1994a). Deoxyadenosylcobalamin performs a key role in the energy metabolism of ruminants by facilitating the metabolism of propionate, which is an important precursor of glucose in ruminants (Kennedy et al., 1991).

Ruminants rely entirely on their rumen microbes to incorporate cobalt into vitamin B₁₂. The vitamin B₁₂ status of the animals is therefore not entirely dependent on the level of cobalt in the soil and diet (Paterson et al., 1989; Reid and Horvath, 1980). The efficiency with which cobalt is incorporated into vitamin B₁₂ by the rumen microbes, the efficiency of absorption and the metabolic demands of the coenzyme-dependent functions are also important factors (Suttle et al., 1991). Dietary levels of cobalt below 0.08 mg (1.4 m mol)/kg DM are regarded as inadequate, but are not invariably associated with loss of production. Soil values of cobalt below 0.3 mg (5.1m mol)/kg soil are regarded as 'deficient'.