Selenium and iodine for breeding ewes

In this study, pre-tupping treatment with rumen boluses containing selenium at 0.1 mg per kg DM was found to provide adequate levels of selenium on a farm known to be deficient in selenium. No differences were observed in ewe condition and weight and lamb growth rates across all levels of selenium supplementation. The effects of supplementing with Iodine were lower than expected at all levels of supplementation. Boluses appeared to have a shorter duration of efficacy and no differences in animal performance were observed across all iodine treatments. Commercially available boluses claim to release selenium, cobalt and Iodine for 180 days; however results from this study suggest that all iodine treatments had limited effect on livestock 3 months  after administration. Reasons for the apparent short duration of efficacy could include:

• Bolus expulsion
• Increased rate of iodine depletion in bolus
• The accuracy of the sampling method (PII)
• A block on iodine absorption through the gastro-intestinal tract

Further research is needed to determine the cause of these results. The findings of this study need to be treated with caution because the data is limited to only one farm for selenium and 2 farms for iodine.

The Problem:                                                                                   

The current recommended dietary allowance of selenium and iodine for sheep are well below recommendations made by NRC (2006). Anecdotal evidence would also suggest that higher levels of selenium could be beneficial in terms of fertility, lamb viability and immunity.  Selenium deficiency is often associated with white muscle disease (WMD), ill-thrift and infertility whereas iodine deficiency is associated with late abortions presenting still-born or weak lambs. Selenium and iodine work together and have a key role in the mobilisation of brown adipose tissue in new-born lambs and therefore also have a role in improving lamb survival.

Aims and Objectives:

Aims

• To compare different levels of selenium supplementation to ewe
• To compare different levels of iodine supplementation to ewes
• To define the requirements for  selenium and iodine in ewes
• Identify production benefits of supplementation under commercial conditions

Deliverables

This will aim to define requirements for selenium and iodine for current breeds of ewe and identify production benefits of supplementation under commercial conditions. The beneficial effects of correct supplementation with selenium and iodine on fertility and lamb survival could have a significant impact on long term sustainability of the sheep industry by increasing the number of lambs reared and reducing GHG emissions per kg lamb produced.

Approach:

Two farms with a low selenium status and two farms with a low iodine status will be sourced. Each farm will have four treatments (one control group with no selenium or iodine supplementation and three groups with selenium or iodine supplementation at different levels).  Supplemented ewes will be given rumen boluses 3 weeks pre-tupping. Ewe and lamb performance will be monitored through till 6 weeks post lambing.