Effect of transient postpubertal hypo- and hyperthyroidism on reproductive parameters of Iranian broiler breeder hens

One hundred and thirty two 26-week-old broiler breeder hens were randomly assigned into one of three treatments as control, hypothyroid (HYPO; propylthiouracil (PTU)-treated) or hyperthyroid (HYPER;thyroxine (T4)-treated) group. PTU and T4 were administered between weeks 30 and 33 of age. Blood sampling was started at week 29, and repeated every week until week 35, coinciding with weekly bodyweighing. Using ELISA, plasma levels of T3, T4 and estradiol were assayed. Egg number, fertility, hatchability, grading of day-old chicks and embryonic developmental stage of unhatched eggs weredetermined for individual artificially inseminated hen. Effects of PTU and T4 treatment on plasma T4 levels were significant (P 0.05). In conclusion, among the different reproductive parameters in this study, hatchability and weekly egg production werethe most responsive parameters to decreased or increased plasma thyroid hormone levels, respectively