Diurnal variations in plasma triiodothyronine and thyroxine levels of the domestic chicken from day-old to egg-producing age
Muray, T.; Pethes, G.; Losonczy, S.; Rudas, P.
Acta Veterinaria Academiae Scientiarum Hungaricae 29(3): 277-281
1981
ISSN/ISBN: 0001-7205 PMID: 6890305 Document Number: 181976
Triiodothyronine [T3] and thyroxine [T4] levels were determined by direct radioimmunoassay in the blood plasma of TR-90 broiler hybrid chickens under 12 h of light-12 h of dark light regime at 1 day, and 3, 15, 21 and 22 wk of age to follow up the diurnal variation of thyroid function. Plasma T3 showed a morning minimum and an afternoon maximum at 1 day and 3 wk of age, but dropped to a lower level at which it persisted practically without fluctuation in a more advanced age (at 15, 21 and 22 wk). The plasma T4 level showed a morning maximum and an afternoon minimum in each age group studied. At 3 wk of age, the T3 level increased considerably over the values found in all other age groups throughout the respective part of the day while T4 level rose only during the morning maximum.