Effects of feeding high dosages of vitamin E to laying hens on thyroid hormone concentrations of hatching chicks

Long-term experimental feeding of 20,000 ppm alpha -tocopheryl acetate to l aying hens caused a significant (P < 0.05) decrease in hatching rates as co mpared to the control group, which was fed a diet containing 19 ppm alpha - tocopherol. When the thyroid hormones in the developing chicks were checked on incubation days 16, 19, 21, and 22, the following results were ascertai ned: During the latter part of incubation, increases in plasma concentratio ns of thyroxine and triiodothyronine were observed. No significant differen ces in hormone concentrations (P > 0.05) between the control and the treatm ent group were observed during incubation days 16, 19, and 22. However, on the day of hatching (day 21 of incubation) significantly lower (P < 0.05) t riiodothyronine concentrations in chick embryos of pipped eggs were found i n the treatment group. Moreover, thyroxine concentrations in non-pipped egg s and in hatched chicks were found to be significantly higher as compared t o the control group. Given these results, one concludes that extremely high dosages of vitamin E may affect thyroid hormone concentrations of hatching chicks, Emd therefore, the chicks might be inhibited in pipping the egg sh ell. Hypothetically, the hepatic enzyme 5'-monodeiodinase is involved in th e mechanism of inhibition. (C) 2001 Wiley-Liss, Inc.