Goitre and Iodine Deficiency

Introduction

The most serious thyroid disorder of farm animals is congenital goitre (goitre that animals are born with) caused by iodine deficiency.

A goitre can be detected as a swelling in the neck by passing the thumb and finger down the windpipe starting just below the throat. In severe cases the enlargement can actually be seen as a swelling in the neck. However, goitre should not be confused with a swelling of the head in newborn animals that results from dystocia, a prolonged or difficult birth.

Congenital goitre occurs most commonly in lambs, less frequently in calves and very occasionally in foals, fawns or piglets. Goat kids are particularly susceptible.

Lambs may be stillborn or weak at birth because of iodine deficiency yet show no visible enlargement of their thyroid gland. Newborn lambs with normal thyroid activity are better able to survive cold wet conditions. A mild deficiency of iodine, causing minimal outward signs of goitre, could be a major contributing cause of young lamb deaths.

Stock owners are urged to submit dead lambs for veterinary examination or to seek veterinary advice when lamb losses are high even if bad weather seems to be the cause.

Causes of goitre

Soil
Most properties on which goitre commonly occurs are in areas associated with the major river systems (Huon, Derwent and the South-Esk - Lake Macquarie system). The sandy textured soils in these regions are lower in iodine than are the clay textured soils.

Climate
Good rains usually result in prolific pasture growth. This tends to lead to the development of goitre by reducing the amount of surface soil eaten by grazing stock. Surface soil, when eaten, acts like a supplement because it contains various minerals including iodine. The amount of soil eaten is also influenced by stocking rates. Goitre is more likely to occur in flocks run at a low stocking rate than in flocks run at a high stocking rate.

Plants
Sheep or cattle fed on brassica fodder crops such as chou moellier, rape, turnips and vegetable crop residues of cauliflower and broccoli are likely to produce goitre in their progeny if access to these crops is prolonged. This is because brassicas contain compounds called goitrogens which interfere with the availability of iodine.

Prevention

Managerial Precautions
If practical, avoid grazing pregnant livestock over 'at risk areas' such as the sandier soil types especially during the latter half of pregnancy.

When pasture is lush and plentiful after a good growing season do not run pregnant stock on these pastures at low stocking rates. In good seasons iodine dosing is a wise precaution in known goitre areas.

Iodine Dosing
Dosing ewes with iodine compounds in the fourth and fifth months of pregnancy prevents goitre in their lambs. The iodine compounds can be given directly or mixed with worm drenches. Recommendations on the dosage and the compatibility of iodine compounds with various drenches can be obtained from your local veterinarian.

Salt Licks
Salt licks containing potassium iodide are likely to lose much of the iodine by evaporation and leaching.

Sodium iodate is more stable in salt mixtures but, as with all licks, not all animals in a herd or flock will use them.

Skin Application
For individual animals, such as goats and for small numbers of ewes or sows, tincture of iodine will prevent goitre in the newborn. It should be painted weekly on the soft skin of the inner thigh during the final six weeks of pregnancy.

Treatment of Goitre

The recommendations for prevention can be adapted for treating goitre in newborn animals. A Veterinarian can provide more specific advice if required.

Painting the teats of sows, ewes, goats and cows with tincture of iodine or an iodophor teat dip once each day for a fortnight, will allow the suckling young to obtain enough iodine to limit development of most goitres.

Summary

A swollen thyroid gland causing a visible swelling (goitre), is the result of a lack of iodine in the dam's diet.

Remember that a deficiency of iodine, causing a lack of thyroid hormone, can contribute to deaths of newborn young even though there is no visible swelling of the thyroid gland to suggest an iodine deficiency.




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