Growth response in lambs injected with a long acting microencapsulated Vitamin B ₁₂

Abstract

Extract

Cobalt (Co) deficiency is an important problem in New Zealand grazing livestock, particularly in young lambs (Andrews, 1965; Grace, 1994). The deficiency is characterised by loss of appetite, poor growth rates and a watery eye discharge (Andrews et al., 1966). In order to synthesise sufficient amounts of vitamin B₁₂ the microorganisms in the reticulorumen require an adequate intake of Co, which for sheep is provided by pastures containing 0.1 mg Co/kg DM. Vitamin B₁₂ is a cofactor for two important enzymes, namely, methylmalonyl coenzyme A mutase and methionine synthase. About half of the glucose required by sheep is acquired by gluconeogensis from propionic acid (Judson et al., 1968) a volatile fatty acid produced in the reticulorumen during fermentation. The propionic acid is converted to succinc acid by the methylmalonyl coenzyme A mutase and the succinc acid is then metabolised to glucose via the tricarboxylic cycle and the glycolytic pathway (Rice et al., 1989). Methionine synthase converts homocysteine to methionine an essential amino acid (Kennedy et al., 1992). Thus Co deficiency impairs the energy and protein metabolism of ruminants.