Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Animal, Dairy, and Veterinary Sciences

Department name when degree awarded

Toxicology Graduate Program

Committee Chair(s)

R. P. Sharma


R. P. Sharma


Art Mahoney


Thomas Bunch


LeGrand Shupe


William Brindley


3,5,6-trichloro-2-pyridinol, when administered in the diet, increases the feed efficiency (the ratio of weight gain to feed consumed) in various species of domestic animals and also appears to be retained in the liver at low concentrations, possibly by binding to a specific macromolecule. Because of its structural similarities to the outer ring of the thyroid hormones, trichloropyridinol and three structural analogs (2,4,5-trichlorophenol, 4-bromo-2,5-dichlorophenol, or 4-iodo-2,5-dichlorophenol) were tested for ability to compete in vitro with 3,5,3'-triiodothyronine (T3) for nuclear receptors specific for the thyroid hormones. All four of the halogenated compounds were found to be weakly competitive for the receptor, indicating a possible anti-thyroid effect.

Weanling male rats were fed diets containing 5, 50, and 500 ppm trichloropyridinol for 30, 60, and 90 days. Other groups received a diet containing 200 and 2000 ppm 2-thiouracil, a known thyroid toxicant. Both chemicals significantly reduced serum thyroxine (T4) levels in a dose-related manner. It was of interest that trichloropyridinol was about as potent as thiouracil in suppressing serum T4 levels. Serum T3 and 3,3'5'-triiodothyronine (rT3) levels were depressed by thiouracil, but generally not with trichloropyridinol. Nuclear T3 binding capacity was not changed in the liver of rats ingesting trichloropyridinol. Body weight, feed efficiency, and organ weights and histology were not significantly altered by the chronic ingestion of trichloropyridinol.

In conclusion, the effects of trichloropyridinol upon animal growth and feed efficiency may involve various mechanisms surrounding thyroid hormone expression including reduction of serum T4 levels and competition with T3 for the nuclear receptor.



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