This study was conducted to evaluate the effects of chronic fluorosis in cows on their blood serum levels of thyroxine (T4), triiodothyronine (T3), and protein-bound iodine (PBI). Data collected from twenty cows with chronic fluorosis in the Tendurek Mountain region (altitude about 2000 m) in East Anatolia, Turkey, were compared with data from ten healthy cows from the Van region (altitude 1700 m). Statistically significant differences (p<0.05) between the serum values in the fluorotic cows and the controls were found: 5.7±0.48 vs 3.7±0.45 ug/dL for T4, 1.53±0.038 vs 0.97±0.051 ng/mL for T3, and 3.8±0.29 vs 2.6±0.23 ug/dL for PBI. Hypothyroidism was therefore evident in the cows with chronic fluorosis.
In this study, the serum levels of thyroxine (T4), triiodothyronine (T3), and protein-bound iodine (PBI) in the control cows were in the normal range of healthy cows, but they were significantly lower (p<0.05) in the fluorotic cows. These findings are consistent with the results of research with sheep, calves, cattle, and rats. . . . On the other hand, Choubisa reported that none of a group of fluorotic domestic animals exhibited any apparent evidence of hypothyroidism, stunted growth, [or] low milk production . . . . In our view, the reason for decreased levels of T4, T3, and PBI in our cows with chronic fluorosis might be due to: 1) inhibition of the absorption of the iodine and some amino acids (e.g., tyrosine) in the gastrointestinal tract, 2) insufficient synthesis and secretion of thyroglobulin and oxidized iodides from the thyroid glands, 3) low levels of bioavailable iodine in the Tendurek Mountain region.