Iodine deficiency

This year, herds in our practice have recorded lower than expected iodine levels. The classical sign of iodine deficiency is thyroid enlargement or goitre seen in young animals. Other signs noticed on farm may include late-gestation abortions, stillborn or weak calves and lambs that are unwilling to suck, more assisted births and increased neonatal mortality.

Iodine deficiency in cattle and sheep is also associated with reduced fertility, growth rates and milk yield. Cows deficient in iodine can also be more prone to retained placentas. If you are having issues with any of the above, contact your vet for a discussion. Submission of samples to the lab will aid a diagnosis and rule out infectious causes.

Severe goitre in calves/lambs will be detectable on exam by your vet or at your local vet lab. More subtle cases may require further investigation, comparing soil and forage analysis in conjunction with animal blood samples.

If these are not available, which is often the case, blood samples taken by your vet can give a snapshot of iodine levels at the time of sampling. Interpretation of iodine status can be multifaceted – your own vet is best suited to interpret and advise based on their knowledge of your herd/flock, area and annual changes.

Iodine deficiency can be primarily occurring where low iodine in the soil leads to reduced iodine in grass and forages. It can also be secondarily occurring due to ingestion of goitrogens found in certain brassicas and legumes, for example fodder beet, kale, rape or white clover.

Selenium is required to activate thyroid hormone and thus selenium deficiency may lead to secondary iodine deficiency. When sampling for iodine, we would usually test selenium levels also.

Methods of supplementation include drenches, boluses, painting 5% tincture of iodine on the flank skin fold, inclusion in concentrates, blocks, licks, and medicated water supply. Some of the above products deliver a cocktail of trace elements and vitamins also. Before using any of these products, it is advisable to identify exact deficiencies on the farm and supplement only according to specific need. Discuss this with your vet.

It is advisable to monitor all trace element levels on a regular basis. The availability of trace elements can change annually depending on weather, reseeding, liming, etc. Where routine supplementation is practiced, monitoring levels in stock is necessary to check that the level of supplementation is adequate. A monitoring programme should be drawn up with your vet as part of a health plan.

Kieran Devaney works at Ormonde Veterinary, 14 Barrack St., Kilkenny. Ormonde Veterinary is part of XLVets. XLVets is a group of progressive practices who are working together to achieve a better future for agriculture and veterinary in Ireland. For further information go to www.xlvets.ie.