Iodine deficiency in sheep and goats

What our vets are seeing across our region

Tablelands Telegraph – October 2020

Lucienne Downs – District Vet

Our District Vets have seen multiple cases of iodine deficiency causing goitre (enlarged thyroid glands) in kids and lambs this spring.

Goitre occurs when there is iodine deficiency during pregnancy. The demand for iodine in the developing foetus is especially high in the final trimester of gestation. In many regions of Australia, the soils are marginal in iodine. In high rainfall areas, levels are likely to be lower.

High autumn rainfall and resulting lush pasture growth will further reduce the availability of iodine in spring when it is most needed in pregnant does and ewes. For this reason, lambs and kids born September to October are most at risk.

Grazing brassica crops or white clover during pregnancy can cause goitre as they contain goitrogens. Goitrogens are substances that disrupt the production of thyroid hormones by interfering with iodine uptake in the thyroid gland.

Overt goitre may be seen in lambs and kids if the thyroids are many times larger than normal. In some cases of iodine deficiency, goitre may not be obvious, or present in few neonates. A ratio of thyroid to lamb or kid weight of more than 0.4g/kg indicates an enlarged thyroid.

In addition to goitre, iodine deficiency can cause abortions, stillbirths and the birth of premature, small and weak lambs or kids. Kids may be born with a sparse hair coat and lambs may be born without wool or appear hairy. Affected neonates have a decreased metabolic rate, impaired lung development and impaired suckling behaviour and have an increased mortality rate from starvation/mismothering. They are especially susceptible to hypothermia.

Prevention and Treatment:

The need for preventative measures will depend partly on the history of the property and herd/flock including a previous diagnosis or suspicion of iodine deficiency, timing of lambing/kidding and seasonal conditions.

As goats have a higher requirement for iodine it has become a standard recommendation that pregnant does grazing in high rainfall areas receive a drench of supplementary iodine once or, in some cases twice, during the last two months of their pregnancy.

Iodine supplementation of ewes depends on the region and seasonal conditions.

Iodised salt licks or iodised salt in the diet may prevent the development of iodine deficiency. Potassium iodide may be given as a drench.

Lambs with goitre can be treated with thyroxine or iodine supplements, however, only slight reductions in the size of the goitre are likely.

An overdose of iodine can result in iodine toxicity so correct diagnosis and supplementation is important. Speak to your veterinarian for advice.

Always report livestock abortions to a veterinarian so that they can investigate to find the cause and rule out zoonotic diseases (those that can cause disease in people) and exotic diseases via lab testing. Testing to show that we are free of exotic diseases supports our livestock markets. It is important to take precautions such as using personal protective equipment (gloves, overalls, boots, masks and googles) and to practice scrupulous personal hygiene when handling placentas and aborted livestock materials.

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