Changes in thyroid hormones concentrations in chicken blood plasma during fattening

Thyroid hormones concentration changes in blood plasma of 30 male hybrid chickens of the heavy Ross breed were studied during broilers ’ fattening period. Blood samples were collected in heparinised tubes after decapitation of chickens at 28, 35 and 42 days of age. Blood plasma was separated by centrifugation and concentration of thyroid hormones triiodothyronine (T3) and thyroxin (T4) was determined by the RIA method. Concentration of both hormones gradually increased during the experiment following the broilers ' fattening process. However, only the increase of T3 concentration was statistically significant. This rise was related to its involvement in metabolic processes, particularly in processes of bio-oxidation. Different dynamics in concentration changes of investigated hormones may be related to an increase in thyroid gland secretion as well as the peripheral conversion of T4 to the reversible T3 (rT3) Key words: triiodothyronine (T3), thyroxin (T4), blood plasma, chicken