Pathological changes in cobalt-supplemented and non-supplemented twin lambs in relation to blood concentrations of methylmalonic acid and homocysteine

In a controlled field study of three years' duration we evaluated the effec t of cobalt supplementation on pathological changes in cobalt/vitamin B12-d eficient Texel twin lambs grazing the same cobalt-deficient pasture. Semi-q uantitative evaluation of the histopathology of liver and brain was done on 44 sets of twins, Pathological changes were related to blood concentration s of vitamin B12, methylmalonic acid, and homocysteine, Lesions were mainly confined to the liver and brain. Acute hepatic changes were characterized by steatosis, hepatocytic degeneration, and single cell necrosis, Chronic c hanges consisted of bile duct proliferation, the presence of ceroid contain ing macrophages, and fibrosis in the portal triads, Many non-supplemented l ambs showed polymicrocavitation and Alzheimer type II reaction in the brain . Polioencephalomalacia was observed in three non-supplemented lambs but wa s regarded as a secondary lesion. Our results indicate that the main lesion s found in cobalt/vitamin B12-deficient lambs are acute and chronic hepatit is. These lesions were associated with low concentrations of vitamin B12 an d high concentrations of methylmalonic acid and homocysteine in the blood, The liver lesions were also associated with polymicrocavitation of the brai n, probably as morphological evidence of hepatoencephalopathy.