An investigation into the methods of improving the cobalt status of soil, herbage and grazing ruminants and its field assessment

In a field trial of two years duration using grazing ewes and lambs an assessment was made of the efficacy of three cobalt (Co) treatment methods, namely, the application of cobalt sulphate to pasture, monthly vitamin B₁₂ injections, and the administration of a slow-release bolus at the start of the grazing season. All three methods led to improved serum vitamin B₁₂ values and liveweight gains, but in terms of cost-effectiveness the application of cobalt sulphate to pasture proved superior, even though this treatment produced a similar or only slightly higher herbage Co concentration than the untreated ground in the second year. The improvement in the Co status of the grazing animals in the second year as a response to applied cobalt sulphate was thought to be due to the ingestion of Co-enriched soil at the start of the grazing season. However, both soil and herbage Co measurements failed to diagnose the Co status of grazing ruminants in response to Co application to pasture. The use of electric shears to sample herbage provided the best prediction of the Co status of sheep based on herbage analysis.