Agriculture Victoria senior veterinary officer Dr Robert Suter said the early season rain that has been welcomed by producers across the state should result in good pasture growth throughout the winter.

However, the flush of new pasture increases the likelihood of trace mineral deficiency diseases in lambs born in winter and early spring.

Dr Suter said trace mineral deficiencies can result from ewes grazing lush green feed during the last half of their pregnancy. 

"These ewes are likely to have lambs with low or deficient levels of trace minerals selenium, copper, iodine and cobalt," he said.

"Sheep ingest several essential trace minerals from soil intake. This usually occurs when ewes graze short pastures after a dry summer and before the autumn break.

"When there is a lot of early season pasture growth, the intake of trace minerals via the soil is less likely to occur."

Growing animals, such as lambs, also have a higher demand for trace minerals than adult sheep and are likely to suffer a dietary deficiency sooner.

Dr Suter said trace minerals such as copper, cobalt, selenium and iodine are only required in small amounts but are still essential for optimal production, and for life.

The signs of deficiency vary according to the mineral involved:

• 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, and ewe infertility are also reported signs 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.
• 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 results in an enlarged thyroid gland, known as ‘goitre' in lambs.

There are effects on the developing foetus including reduced foetal size, brain retardation and increased lamb mortality.

Dr Suter said sheep producers in known deficient areas should review their trace mineral supplement strategies to ensure ewes have adequate levels to produce healthy lambs.

"Most of Victoria is iodine deficient; and an appropriate time to supplement ewes is mid-pregnancy," Dr Suter said.

"A good time to do this is at pregnancy scanning. Special care must be taken with supplementing ewes with copper, as sheep can be easily killed with relatively small amounts of copper."

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