Abstract
Experiments were conducted to determine the effect of ambient temperature, 5, 20, or 35°C, on thyroxine secretion rate (TSR) and on thyroid epithelial-cell height. Male chicks were treated for a 10-day period for the TSR determination by the goiter prevention method, and for a 11-day period for the the measurement of epithelial-cell height.
Exposure to 35°C, starting at 28 days of age, caused a significant reduction in TSR and epithelial-cell height, when compared with exposure to 5 and 20°C. The results obtained at temperatures of 5 and 20°C were not significantly different.
The reduction in epithelial-cell height was observed on the 4th day of the treatment. A similar effect was obtained when the treatment (35°C) was started at 14 days of age.
Consequently, it was proved that the thyroid activity determined by two methods is reduced by ambient temperature of 35°C for a 10-day period, but not at 5 and 20°C When 14- or 28-days old chicks are employed.
A trial was made to investigate the influence of the administration of thiouracil from 28 days of age on feed consumption and body weight, when treated at 20°C. It was confirmed that the administration of thiouracil adversely affected on feed consumption and body weight during the first 2 days of treatment, subsequently recovered to some extent.
