Do my sheep need trace elements this year?

Dr Jeff Cave, senior veterinary officer, Northern Region

Do you sometimes wonder whether your stock has a trace element deficiency? If they do, is it likely to be all of them or just some groups? Is it likely to be all the time, or is it associated with seasonal conditions? Plus, which trace elements should I be concerned about on my farm?

When are trace element deficiencies most often seen?

Trace element deficiencies arise when there is an insufficient amount of the mineral ingested available for absorption by the animal through their gut to meet their needs.

The ingestion of soil is an important source of trace elements for an animal. Soil ingestion usually peaks when ewes graze short pastures after a dry summer and before the autumn break. On many properties in Victoria this year, soil ingestion would have continued at a higher level than normal through autumn, winter, and early spring.

Furthermore, lush, rapidly growing pasture is lower in trace minerals than slow-growing or mature pasture. Hence, trace element deficiencies are more often seen during spring in the more favourable years. It may seem counterintuitive to be less worried about trace element deficiencies in poorer years.

Young growing animals have the highest demand for trace minerals. For example, growing lambs need about twice the selenium in their diet that adult sheep require. They are also born with minimal reserves stored in their body, so a dietary deficiency will become apparent sooner than in an older animal with previous body stores.

What are the primary trace element deficiencies in Victoria?

The trace elements of most significant concern in Victoria are selenium, copper, cobalt and iodine. The likelihood of a deficiency varies markedly across the state. It is worth researching which of those trace elements are most likely to be an issue on your property.

Selenium deficiency causes ‘white muscle disease’ with white lesions in the red skeletal and cardiac muscle tissue, leading to lameness or sudden death. Ill-thrift reduced wool growth. Ewe infertility is also reported as a sign of deficiency.

Copper deficiency presents most dramatically as enzootic ataxia (or ‘swayback’), a condition causing paralysis of the hind limbs of newborn or very young lambs. Less apparent signs include steely wool, anaemia and reproductive loss in older sheep. Special care must be taken when supplementing ewes with copper, as sheep can be easily killed with relatively small amounts.

Cobalt deficiency is an ill-thrift disease of reduced appetite and growth, decreased wool production, anaemia and poor reproductive performance. Affected animals often have ‘white liver’ disease. Diagnosis is based on vitamin B12 levels (vitamin B12 contains cobalt), and treatment is with vitamin B12.

Iodine deficiency leads to a lamb with an enlarged thyroid gland, known as goitre. The lamb will be undersized or stillborn, have a reduced wool cover and be weak and susceptible to cold stress. Cases of goitre typically occur after 3 consecutive months of 80 ml or more of rain. To prevent goitre, an appropriate time to supplement ewes with iodine is mid-pregnancy, through giving iodised salt or a potassium iodide drench.

It’s worth remembering that a trace element deficiency may present as a suboptimal drop in production without any clinical signs.

How do you supplement and test for trace element deficiencies?

Once you have identified the trace elements of greatest concern on your property, it is then worth considering how you would supplement your livestock as a preventative measure using drenches, rumen boluses, and/or injections, with a particular emphasis on young, growing animals during seasons of plentiful pasture growth.

It is also worth considering testing at-risk stock to help decide whether they need trace element supplementation.

For more information or advice, speak to your local veterinarian or Agriculture Victoria animal health staff.