Iodine is essential as a constituent of the thyroid hormones, in particular T3 and T4, and 80 per cent of the iodine in the body is found in the thyroid gland. The classical sign of iodine deficiency is thyroid enlargement (goitre) due to compensatory mechanisms invoked by the lack of thyroid hormone production. The swelling of the thyroid gland is located in the neck region posterior (far end of the neck) and ventral larynx (part of the throat that mostly contains vocal cords). It is a condition mostly common in areas such as Maun, Letlhakane and Francistown veterinary districts (Mushi et al., 1999).
- Natural deficiency in the soilsleads to primary deficiency. Sandy soils are leached by rain which results in the loss of iodine from the soil and therefore forage.
- Secondary deficiency results from ingestion/feeding on forages such as Brassica spp. Such as kale, rape and cabbages, as well as legumes like Cynadon leucoena which contain substances (goitrogens) that inhibit the accumulation of iodine into the thyroid gland.
- Selenium is required for the conversion of T4 to active T3, and thus selenium deficiency may lead to secondary iodine deficiency states.
- Abortion and hairless fetuses.
- Weak new borns which cannot survive cold stress.
- Susceptibility of these new borns to respiratory problems.
- Swollen thyroid gland.
- Low libido.
- Retarded growth and reduced appetite.
- Silent heat leading to infertility.
- Poor milk production.
- Retained placenta.
Diagnosis (how it can be recognized)
- Signs shown by the young and adult animals.
- Report the case to the district veterinary officer who will then collect serum from the females and the young for thyroid hormone assay.
- Dead young should be submitted to the National Veterinary Laboratory for post-mortem and histopathological studies on the thyroid gland.
Treatment and prevention
- Give young or all animals iodized salt licks.
- Sprinkle salt on feed of older animals.
- Iodine is frequently added to concentrate rations for feeding to cattle.
- Free-access minerals, medication of water supplies and pasture fertilizers can all be used to varying effect.
- Dose with potassium iodide, 2 months before and again 2 weeks before birth.Dosage: – Dissolve 20g of potassium iodide in 1 liter of water and use at a rate of 10ml/20kg live weight.
- 3-5 drops of Logul’s iodine in the young’s drinking milk, once a week.
Note: a high dose of iodine results in toxicity!
Signs of iodine toxicity
- Refusal of feed
- Watery eyes
- Hair stands out of its end.
Do not feed thyroid gland function-inhibiting substances (goitrogens) such as rape, kale cabbage etc.