The effect of excess dietary iodine on pregnant mares and foals.

The research analyzes the effects of excessive iodine intake in pregnant mares on their offspring, with the study observing thyroid enlargement and leg weakness in foals, attributing these effects to the high iodine content in the mares’ diet.

Research Context

• The study was carried out on a thoroughbred stud where four foals were born with significantly enlarged thyroids and leg weakness. Among them, two died within 18 hours of birth, while the others managed to recover over time. An enlarged thyroid was identified in one resident mare as well.
• The researchers closely examined the conditions surrounding the foals’ births, which included analyzing the horse feed’s constituents and investigating the health conditions of the stud’s resident mares.

Pertinent Findings

• Upon examination, the researchers found that the thyroids from the dead foals were hyperplastic, i.e., they showed an abnormal increase in volume due to the rapid growth and multiplication of the constituent cells.
• The examination of the feed showed that the mares had been intaking about 83 mg of iodine daily, 8-8 parts per million (ppm) of the dietary dry matter. This high iodine content was almost entirely owed to a proprietary compound horse nut that was being fed to the horses at twelve pounds per head daily.

Conclusions

• Considering the histology of the thyroids, the excessive iodine intake, the non-response to potassium iodide treatment, and the elevated levels of serum protein-bound iodine, the researchers concluded that the conditions observed in the foals on the stud were more likely an outcome of the excess iodine consumed by the mares during pregnancy.