Iodine deficiency

By: Seyedamin Razavi

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This can be the result of a primary lack of iodine. Secondarydeficiency is recorded following high intakes of brassicas, highcalcium ingestion, and plants containing cyanogen glycosides.Iodine deficiency occurs in most parts of the world wherethere is a high rainfall and there is little exposure to oceaniciodine. Soils with a high calcium content are likely to bedeficient. The condition is mainly seen in the newborn. Iodineforms part of them hormone thyroxin, and a deficiency willresult in them pituitary increasing the production ofthyrotrophic hormone. This in turn leads to goiter.

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Signs: Many of the affected calves are aborted or stillborn andusually there is evidence of thyroid enlargement (goiter). If theanimal is born alive it will be weak and disinclined to suck.Occasionally, the gland will be felt to pulsate. Very rarely areasof alopecia are apparent.

Necropsy: The thyroid glands are enlarged and heavier thanusual (normal fresh weight 6.5 g; a weight greater than 14 gis suspect). Histologically, there is thyroid hyperplasia.

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Diagnosis: Diagnosis depends on the area or a diet containinggoitrogenic plants. There is thyroid enlargement in thenewborn and several heifers or cows abort or producestillborn or weak calves. Plasma protein-bound iodine levelsare low. The plasma inorganic iodine can be used. Most (90per cent) of circulating iodine is bound as thyroxin and normalvalues are 36–89mg/l (80–160 moll/l). The thyroid weight isincreased and the iodine content of the gland is low.Differential diagnosis is mainly to eliminate other causes ofabortion.

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Treatment and prevention: Treatment is to ensure that the calfsucks and is kept in a warm, draught-free environment. Thyroidextract can be used at a dose of 1–2mg/kg body weight.Intravenous sodium iodide can be used at a dose of 5–7 g for theyoung calf, but it is not without risk; potassium iodide can beused orally at about 3g per calf. iodine poisoning can sometimesdevelop. Prevention involves allowing the dams adequate iodinein the diet. A recommended level is 0.8mg/kg DM for pregnantand lactating cows. The level for calves should be 0.12mg/kgDM. A bolus of 3400 mg iodine with selenium and cobalt canrelease iodine for five to six months. Some fertilizers are high iniodine and seaweed meal can be given in the feed and typicallycontains 50–100mg/kg DM iodine.

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