Managing trace element deficiencies in sheep

Summary

This Producer Demonstration Site will demonstrate appropriate practices for diagnosis of trace element deficiencies (i.e. blood tests, liver samples/biopsies for Cu) and use leaf analysis to highlight seasonal variation in clover & grass mineral status. The benefits of using the EID technology to collect and collate data will also be demonstrated.

Objectives

By October 2023, in the East Gippsland region of Victoria:

1. Ascertain the trace element status of 10 flocks in east Gippsland

2. Demonstrate and assess the effect of different trace element treatment options on (In flocks identified to be deficient in one or more trace elements):

   a. Live-weight gains of Merino and Composite/Cross-bred lambs

   b. Wool production of lambs at their lamb shearing plus hogget shearing for self replacing flocks

   c. The reproductive rate (Scanning % and marking %) of Merino and Composite ewes

3. Conduct a cost-benefit analysis to determine the relative economics of the different treatment options used on each farm.

4. Conduct an annual field day and other activities to showcase the demonstration site results and encourage adoption of key practices by the group and other regional producers.

Progress

The Bairnsdale Bestwool/Bestlamb group in East Gippsland in Victoria set out to demonstrate best practice for the diagnosis of trace element deficiencies in sheep flocks and conduct cost-benefit analysis of preventative treatment options.  

The trace element status of 10 flocks was determined from a blood testing program that occurred in spring 2020.  Marginal blood selenium levels (GSHPx between 20 and 50 U/gHb) were found in composite, first-cross and Merino lambs on 5 farms and deficient levels (less than 20 U/gHb) in Merino lambs on 1 farm.  Marginal blood vitamin B12 levels (between 200 and 400 pmol/L) were found in lambs on 1 farm.  Following weaning, five producer demonstration sites were established to assess the effect of selenium and cobalt/vitamin B12 supplementation on sheep live-weight gains, wool production and reproductive rate. Four farms compared a “Control” group of lambs (no trace elements), a “Farm practice” group (occasional use of short acting products) and a “Long acting” group (rumen pellets). The fifth farm compared 2 different short-acting injection regimes and a long-acting treatment, and did not have a Control group (as was very deficient in selenium and cobalt).  Trial sheep were blood sampled 3 months and 12 months post treatments. The demo sites were monitored until June 2022, which covered 2 springs and by which time sheep were nearly 2 years old.    

On the four farms with a Control group, no major production responses were measured from administering selenium or cobalt. The fifth farm, with no Control group, found that the 2 different regimes of short-acting injections used regularly were able to maintain adequate blood selenium and vitamin B12 like the long-acting rumen pellets, but they were a more expensive option and involved more labour for the yarding and injection of sheep.  

The response trials highlighted that where sheep tested marginal or at the low end of the normal range for selenium or vitamin B12, there were no production benefits from supplementing selenium or vitamin B12. Although the east Gippsland region has soils that are low in trace elements, deficiencies in sheep do not occur every year and different farms will have different risk factors. Blood testing is an important diagnostic tool to determine the trace element status of young sheep and whether they are at risk.