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

Key findings

Marginal blood selenium levels (GSHPx activity) were found on 5 farms, and deficient levels found on 1 farm, at either the pre-marking or pre-weaning sampling.

Low blood vitamin B12 levels were found on 3 or 4 lambs on 2 farms at the pre-marking sampling and did not appear to be an issue at the pre-weaning sampling.

For the 4 farms that had marginal blood test results for selenium and included a nil/Control treatment, no production responses to selenium or vitamin B12 were measured in the response trials.
The fifth farm did not include a nil/Control treatment, due to severe deficiency of selenium and cobalt in the lamb blood tests. The producer found that 2 different regimes of frequent treatment with short-acting Se and vitamin B12 injections were able to maintain adequate blood Se and B12 levels in the weaners as did the long-acting rumen pellets. The use of long-acting products would reduce product costs and labour.

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. The response trials found that there were no production benefits from administering selenium supplements where sheep tested marginal or at the low end of the normal range for selenium. This is consistent with the findings of experiments conducted in the 1970s and 1980s in Victoria, where responses were only obtained in flocks with very low selenium nutrition (blood GSHPx < 20 U/gHb).

Both the Core and Observer producers increased their knowledge on the PDS topic (scores lifted from 68% to 88% Core and from 54% to 84% Observer) but it was the core producers who dramatically increased their confidence in managing the issue due to their active participation in running the trials on their own farms.

Benefits to industry

This project is relevant to all sheep and cattle producers in east Gippsland as well as producers in other regions known to be marginal for trace elements such as south Gippsland, parts of north-east Victoria, south-east South Australia and King Island.

If not treated, trace element deficiencies cause major reductions in livestock production. Sub-optimum growth rates in lambs reduces the efficiency of pasture utilization, delays sales, increases risk and may lead to higher mortality. Poor mineral nutrition of ewes could affect their reproductive performance and longevity. Conversely, treating sheep that are not deficient increases the cost of production of meat and wool and in the case of Cu could be toxic to sheep.

Correct diagnosis and information on likely response is required to help producers, in all districts known to be marginal for trace elements, plan the most cost-effective preventative treatment program.

MLA action

MLA continues to deliver the Producer Demonstration Site (PDS) program, supporting livestock producers working in peer-to-peer groups to pursue new skills, knowledge and management practices applicable to their own commercial livestock production systems.

Future research

For producers with severe deficiency of selenium or cobalt, long-acting rumen pellets (3 years) are what have been used traditionally. The pellets are slow/labour intensive to administer but prevent the need to come back with repeated injections as per the short-acting products. For producers with a severe selenium deficiency, the availability of a long-acting selenium injection (18 months) can be a more labour and cost-effective option than pellets. The product gap in Australia is in the availability of a long-acting vitamin B12 injection (12 months) which is available in New Zealand and produced by Virbac (called SMARTShot B12).

There are currently no plans by the company to make it available in Australia. Perhaps future response trials could include this product to evaluate against the other options.
Animal health products containing selenium and vitamin B12 are readily available in rural merchandise stores in all districts and are widely promoted to sheep producers. Inclusion of trace elements significantly increases the cost and in many districts they are not needed.

More independent testing/evaluation and information about products is required to help producers in different regions make more informed decisions about whether to use a product and the cost-benefit. These evaluations could be supported by producer groups to customise them to the region.