Hyperplastic goiter in two adult dairy cows

Area of Science:

• Veterinary Medicine
• Endocrinology
• Animal Nutrition

Background:

• Iodine excess and hyperplastic goiter are known in young ruminants.
• Limited data exists on iodine excess effects and thyroid histology in adult ruminants.

Observation:

• Two adult Holstein cows presented with nonspecific illness and were necropsied.
• Grossly enlarged thyroid glands were observed in one cow.
• Histological examination revealed cystic nodular hyperplasia and follicular atrophy in both cows' thyroids.

Findings:

• Both cows exhibited markedly elevated thyroid iodine concentrations.
• Investigation identified multiple supplemental iodine sources and poor feed mixing on the farm.
• Adult cattle are susceptible to excessive iodine doses, leading to nodular hyperplastic goiter.

Implications:

• Accidental excessive iodine supplementation may be common in adult dairy herds using iodized salt.
• Recognizing specific thyroid gland changes (cystic hyperplasia, atrophy, fibrosis) should prompt suspicion of iodine imbalance.
• Serum iodine measurements are crucial for diagnosing suspected cases of iodine toxicity or deficiency in cattle.