Iodine is essential for the production of thyroid hormones which control energy metabolism and protein synthesis. Iodine intake is most critical during pregnancy when the dam must provide enough iodine for the growing foetus.
Signs of iodine deficiency include decreased scanning percentage in sheep, goitre in newborn animals (seen as a swollen neck), low birth weights and poor survival as neonates are weak and more susceptible to cold stress.
Many cases of iodine deficiency are caused by goitrogens in the feed. Goitrogens are present in certain brassicas and clovers in New Zealand and act by preventing the uptake of iodine by the thyroid gland.
Unfortunately there are no reliable tests for iodine status in the live animal. The best test, if iodine deficiency is suspected, is for your vet to post-mortem some of the dead newborn lambs/calves. As well as general observation, the weight of the thyroid gland is compared to the body weight of the newborn to determine if the dam was iodine deficient during her pregnancy. A supplementation plan can then be put in place to prevent it happening again.
Urine and blood iodine tests are available for sheep and cattle. However, these tests have limitations and on their own are generally not reliable tests of iodine status.
Dairy cattle on farms that use an iodine teat spray are likely to be receiving adequate iodine. Intake levels may be inadequate over the dry period especially if the cattle are grazing brassicas. Treatment of water with iodine is usually the simplest way of supplementing.
Iodine deficiency in ewes can be prevented with iodine drenching from mid-pregnancy or a long-acting iodine injection pre-mating.
The type of supplementation suitable for your farm will depend on the level of risk, whether or not goitrogenic crops are being fed and the history of iodine deficiency on the property.
