Goiter an indication of iodine deficiency
The thyroid gland, nestled against the upper trachea, produces the two key thyroid hormones the body needs for normal function and metabolism.
Goiter is the term for abnormal, non-cancerous swelling of the thyroid gland.
These swollen glands can develop in a wide range of animals, including mammals, reptiles and birds.
Among domestic animals, species most often affected by this condition are sheep, goats, cattle and pigs.
Foals can develop fetal thyroid issues, but the cause of this condition, known as congenital hypothyroidism and dysmaturity syndrome, is complex and the outcomes severe.
The most common cause in Western Canada is iodine deficiency.
Soil with low levels of iodine produce plants that are also deficient in this critical mineral, leading to feed that can’t provide enough iodine to animals. Pregnant female animals fed iodine deficient diets can give birth to offspring that have goiters.
Other causes of goiter occur less frequently, including excessive dietary iodine.
Goitrogenic components in the dam’s diet can also lead to this condition.
Plants produce molecules that inhibit thyroid hormone production. When there are low levels of thyroid hormones in the blood, the body signals the thyroid gland to produce more, which leads to the tissue swelling.
Plants commonly associated with this issue include soybeans and the brassica family, which includes canola, kale, turnips and cabbages.
Adequately heating the feed destroys these harmful compounds.
As well, hereditary goiters have been detected in pigs, sheep, goats, cattle and dogs.
The genetic defect reduces the ability for the thyroid gland to produce adequate hormone levels, resulting in the same signals as other causes and goiter development.
These are rare and are thought to be recessive traits, making it possible to control through selective breeding.
Iodine is a critical structural component in thyroid hormones, but animals that have low iodine levels are often not able to produce enough of these hormones.
Thyroid hormones are critical for many bodily functions, which is why an improperly functioning thyroid gland can have devastating effects on a growing fetus.
As with many mineral imbalances, it is the fetuses and young animals most severely affected.
Goiter is rare in adults; thyroid swelling in mature animals should be examined for potential tumours.
Why does the thyroid gland swell like this?
Due to low iodine or other causes, there is not enough thyroid hormone in the system. The body signals over and over again that the gland should put more thyroid hormones into the blood.
However, when there is not enough iodine, the gland grows to try to meet the demand. Often in fetuses and young animals, even with the tissue swelling, the thyroid gland cannot produce enough thyroid hormones.
The disease is confirmed clinically or during an autopsy examination based on the presence of a large swelling in the throat that corresponds to enlarged thyroid glands.
Microscopically, the tissues are busy with too many cells. Importantly, there is no inflammation or cancerous changes.
Goiters in fetuses and newborns can also be accompanied by an underdeveloped hair coat and slow growth.
Some animals also get swelling in the skin, making their eyelids and muzzle look abnormally puffy.
Other causes of swelling in the throat area include lymph node infections, salivary gland infections and edema (sometimes referred to as bottle jaw). An examination by a veterinarian, possibly with assistance of ultrasound, can distinguish these.
Negative outcomes can include abortion, stillbirths or newborns that are weak or poor doing.
Those that are born alive may develop infections such as pneumonia and diarrhea, or be particularly sensitive to poor environmental conditions.
At a herd level, these negative outcomes can be further investigated by submitting one or more deads for an autopsy and additional testing that may include mineral levels.
Prevention involves checking feed levels and providing supplemental iodine, usually in the form of iodized salt. Treatment is similar and involves providing supplemental iodine to the affected herd or flock.