Investigation of changes in thyroid hormones and blood metabolites in broiler breeder hens after peak production

Trend in body weight, thyroid hormones and some blood metabolites changes in broiler breeder hens after the peak egg production was studied. Blood samples from 20 Ross 308 broiler breeder hens, were investigated from 47 to 55 weeks of age. Plasma lipid profile including cholesterol, triglyceride, lipoprotein LDL, lipoprotein HDL, and also glucose concentrations were measured every two weeks, and plasma concentrations of triiodothyronine (T3) and tetradothyronine (T4), aspartate aminotransferase (GOT) and alanine aminotransferase (GPT) were measured at the beginning and at the end of the experimental period. Results showed that body weight and plasma concentration of glucose, triglycerides, cholesterol, and LDL were increased, and concentrations of HDL were decreased (P<0.05) over the experimental period. Plasma T4 concentrations were decreased with age of the birds (P<0.05), while T3 concentrations were not affected. Plasma GOT and GPT enzymes activities were increased over the experiment period (P<0.05). In general, by increasing of age and subsequently body weight of breeder hens, several major changes have been occurred in blood metabolites and metabolic hormones which could reduce production and reproduction of broiler breeder flocks.