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Cobalt Supplementation

Teagsac researchers, Tim Keady and Daniel Hession discuss cobalt supplementation to lambs post weaning and ewes pre joining.

Main Messages

  • 69% of farmers supplement their ewe and/or lambs annually
  • 35% of supplementation decisions are based on laboratory analysis and/or veterinary advice
  • 73% of farms have deficient herbage cobalt concentrations
  • At Athenry cobalt supplementation
    • had no beneficial effect on ewe productivity
    • increased post weaning lamb performance 
    • No benefit to including B12 with cobalt on lamb performance


High levels of lamb and ewe performance are readily achievable from grazed grass offered as the sole diet.  However, many producers report that they are unable to finish lambs from grazed grass alone.  Whilst the reasons for this inability are likely to include grassland management practices and parasite control, mineral (trace element) deficiency can be an issue. 

Recent results from the Teagasc National Farm Survey show that 69% of Irish sheep farmers supplement their flock (ewes and/or lambs) with minerals at least once annually. The most used methods are drenching for lambs and mineral buckets for ewes. Only 35% of farmers who supplement base their decision on veterinary advice or laboratory analysis. 

Trace element deficiency

The main trace elements of concern in sheep production are cobalt and selenium. Results from a recent survey undertaken on 56 lowland sheep farms throughout Ireland showed that, based on NRC requirements, herbage on

  1. 73 % of farms had deficient cobalt concentrations
  2. 11 and 89% of farms had deficient and marginal selenium concentrations, respectively

The concentration of trace elements in pasture varies during the grazing season. From a recent study involving 56 farms throughout Ireland mean herbage cobalt concentration tended to decrease from March to June and increase from August to October. Mean herbage selenium concentration tended to increase from May to August. 

Cobalt is required by sheep for the synthesis of vitamin B12 in the rumen. Symptoms of deficiency include loss of condition, poor fleece quality, ears become dry and scaly (photosensitisation), loss of appetite, runny eyes with tear staining on the face, and raised worm counts (immune suppression). As cobalt is not stored in the body and is needed in the rumen, a continuous supply is required throughout the grazing season for vitamin B12 production.

Selenium deficiency is associated with poor lamb performance and white muscle disease.  Its metabolism is closely related to vitamin E which acts as an antioxidant.

Athenry ewe study 

In a recent study the effects of supplementation with cobalt, and method of administration (drench, bolus), on ewe reproduction and offspring performance to weaning were evaluated. There were 3 treatments: no supplementation (control), cobalt only drench cobalt only bolus. The ewes on the cobalt drench treatment received a drench ewe 2 weeks from 7 weeks pre-joining until 6 weeks prelambing. The ewes on the bolus treatment received a bolus at 7 weeks pre joining. 

The effects of cobalt supplementation and method of supplementation, on ewe performance and the performance of their progeny to weaning is presented in Table 1. Supplementation with cobalt, either by drench or bolus, had no benefit on litter size or the number of lambs reared. Lamb weight at birth or at weaning was not improved by cobalt supplementation, either by drench or bolus.

Athenry lamb study

In a recent study the effects of supplementation with cobalt, either alone or in combination with vitamin B12 and selenium, on lamb performance post weaning were evaluated. There were 3 treatments: no supplementation (control), cobalt supplemented alone, or a combination of cobalt, vitamin B12 and selenium. The lambs received their treatments, by drench, every 2 weeks. Lambs were drafted for slaughter at regular intervals when they had achieved target liveweight.

During the first 7 weeks of the study (July/August) trace element supplementation had no effect on growth rate. However, as the grazing season progressed supplementation with cobalt, either alone or in combination with vitamin B12 and selenium, increased lamb weight gain. Consequently trace element supplementation increased average weight at drafting and carcass weight by 2.1 kg and 1.4 kg, respectively (Table 2). There was no benefit from including vitamin B12 and selenium with cobalt under the conditions of the Athenry farm.