The effect of levamisole treatment every 3-4 weeks, cobalt therapy, or both, on the performance of yearling cattle grazing together on known cobalt-deficient pastures on a siliceous sandy soil in south-eastern Queensland was studied between August 1978 and October 1979. In the first stage of the observations, from August to March, the responses (Pc0.05) in liveweight gain compared with the controls (C) were 18, 54 and 75 kg for levamisole (L), cobalt bullets (B), and both (LB) respectively. Thus the responses were additive with no interaction. Deaths were recorded in the control and levamisole only groups in March. Steers in the levarnisole only group were treated with cobalt in March (L + B). Liveweight gains between March and October were 9, 71,47 and 41 kg for C, L + B, B and LB groups, respectively (L + B > B, LB > C, P< 0.05). Cobalt therapy increased faecal worm egg counts in undrenched groups between November and April (P<0.05). At 30 weeks after the start of the study many animals in groups C, L and B were anaemic. Cobalt concentrations in green panic ranged from 0.015 to 0.029 �g/g dry matter and in Siratro from 0.036 to 0.048 �g/g dry matter.

The response to cobalt therapy of weaned calves grazing green panic-siratro-Townsville stylo pastures, on a siliceous sand in the coastal foothills of south-east Queensland was measured. Overall liveweight gains for weaners given a 30 g cobalt bullet following weaning (May), or a cobalt bullet in the following spring (November), or the untreated (control group), were 0.24, 0.18 and 0.08 kg day-' respectively. Twenty-five percent of the calves in the control group died. These deaths were associated with anaemia in the presence of low to moderate levels of helminths. Twelve percent of animals in the cobalt-treated groups died due to an anaemia associated with helminth infections, comprising mainly Haemonchus placei. Faecal worm egg counts in cobalt-treated groups were higher than in controls on two collection dates in December and March, but differences were significant (P < 0.05) at the second date only, when larval differentiation showed 82% H. placei. Cobalt levels in samples of siratro and green panic were in the range 0.01-0.07 ppm. It is concluded that cobalt therapy will eliminate weaner ill-thrift on these siliceous sands but may lead to increased infections of H. placei.

Surveys by the USDA confirm that bovine respiratory disease (BRD) is the leading cause of death of nursing (preweaned) beef calves three weeks of age and older. Management modifications decrease BRD in some cattle populations; however, management-related risk factors for BRD in nursing calves are poorly characterized, making it difficult to develop evidence-based control measures.