Iodine deficiency is common in animals which are grazed in areas with low soil iodine levels. Goats are particularly sensitive to iodine levels, and in areas of known low soil levels, routine supplementation should be established. This supplementation could be by feeding or providing appropriate salt licks. Some keepers choose to take a more active approach and drench all animals with a solution of 2% potassium iodide at a rate of 10mls per 20kg. The particularly important periods within the breeding cycle are:
- 4 weeks prior to mating
- 6-8 weeks prior to kidding
- 2 weeks after kidding
The requirement for iodine
The thyroid gland requires iodine to produce thyroxine, which is implicated in growth and development of animals both before and after birth. Thyroxine is not transferred across the placenta, and the thyroid gland of a fetus is responsible for adequate production of thyroxine from around half way through gestation. In the absence of sufficient iodine, the thyroid gland is continually stimulated to produce thyroxine which it cannot due to the lack of the vital ingredient. The stimulating hormone (Thyroid Stimulating Hormone, TSH) eventually causes a functional change in the thyroid tissue and the gland enlarges.
The classic appearance of iodine deficiency in a herd is the production of weak, poor growing kids, with a sparse hair coat. These animals may or may not have an enlargement of the thyroid glands (goitre). If swelling of the neck is seen in a well-growing healthy kid, then Milk Goitre should be considered. True goitre can be difficult to detect until it is advanced, since the thyroid glands sit behind the larynx. Milk goitre appears in front of and on both sides of the larynx.
High levels of iodine will also cause a swelling of the thyroid glands. These animals are hyperthyroid. The goitre is the result of hormone synthesis blockage by excess iodine uptake (called the Wolff-Chaikoff effect). The fetal thyroid gland is very sensitive to high levels of iodine and kids born to does with high levels are born with obvious thyroid swellings.