Cobalt supplementation - effect on ewe and lamb performance

The productivity of Irish lowland flocks is low at approximately 1.3 lambs reared per ewe joined, and has remained relatively static for the last 40 years. In this article, Dr. Tim Keady, Teagasc Athenry, looks at the effect of cobalt supplementation on ewe and lamb performance.

Whilst high levels of lamb performance is consistently achievable from grazed grass offered as the sole diet, many producers report that they are unable to finish lambs from grazed grass alone.

Whilst the reasons for producers inability to finish lambs from grazed grass or the lack of an increase in ewe productivity are likely to include ewe genotype, grassland management practices and parasite control, mineral (trace element) deficiency can be an issue.

Cobalt

Cobalt is an essential mineral for sheep as it is a component of vitamin B12, which is acquired by ruminants from the B12 synthesised by rumen microorganisms. 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.

Trace element deficiency

Two of 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 73% of farms had deficient cobalt concentrations whilst herbage on 11 and 89% of farms had deficient and marginal selenium concentrations, respectively.

Athenry ewe study

The effects of supplementation with cobalt, and method of administration (drench, bolus), on ewe reproduction and offspring performance to weaning were evaluated in a recent study at Athenry. There were three treatments: no supplementation (control), cobalt only drench and cobalt only bolus.

The ewes on the cobalt drench treatment received a drench each 2 weeks from 7 weeks pre-joining until 6 weeks pre-lambing. The ewes on the bolus treatment received a bolus at 7 weeks pre joining. The mean cobalt concentration of the grazed grass was 0.10 mg/kg dry matter. Mean plasma concentration of vitamin B12 was marginal or low for 64 and 44% of the ewes which received no supplementation (control) in years 1 and 2 of the study, respectively. 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.

Table 1: Effect of trace element supplementation on ewe and lamb performance

Athenry lamb study

The effects of supplementation with cobalt, either alone or in combination with vitamin B12 and selenium, on lamb performance post weaning were evaluated in a recent study at Athenry. 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 2.1kg and 1.4kg, respectively (Table 2). There was no benefit from including vitamin B12 and selenium with cobalt under the conditions of the Athenry farm.

Table 2: Effect of trace element supplementation on lamb performance

This article first appeared in the Teagasc Sheep Open Day booklet 2022.