Experiments were designed to investigate the effect of sub-clinical cobalt deficiency in pregnant hill sheep, on lamb viability. This form of the deficiency is not characterised by clinical symptoms. The disease is therefore difficult to detect, and may be of economic importance to farms on land of marginal cobalt status.

In each of two trials, both with sixty Scottish Blackface x Swaledale ewes, animals were randomly assigned to three treatment groups: A. Cobalt-deficient intake throughout pregnancy; B. Initially cobalt-sufficient intake, but deficient from mid-pregnancy (Trial 1) or initially cobalt-deficient intake, but repleted from mid-term (Trial 2); C. Cobalt-sufficient intake throughout pregnancy. A cobalt-deficient ration (<0.06 mg Co/kg DM) of Timothy hay, micronised maize and maize gluten, was fed from tupping in Trial 1, and from two months before tupping in Trial 2. Treated animals received a weekly oral dose of 0.7 mg Co/head.

Vitamin B12 (microbiological and radio-immuno assays) and methylmalonic acid (capillary gas chromatography) were analysed in ewe and lamb sera, as indicators of cobalt status. Levels of passively acquired immunity were measured by analysis of lamb sera, sampled at two and four weeks post-partum, for immunoglobulin G (IgG) and by the zinc sulphate turbidity test (ZSTT).