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

Abstract

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 body
weighing. 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 were
determined for individual artificially inseminated hen. Effects of PTU and T4 treatment on plasma T4 levels were significant (P < 0.05), but T3 levels were only affected by PTU. No significant effect was observed in plasma estradiol levels. Increased body weight following PTU treatment was not observed in other groups. Weekly egg number of HYPER was significantly lower (P = 0.0435) than other two groups, while the effect of PTU was not significant. Hatchability of fertile eggs (%) in HYPO was significantly decreased (0.00%, P < 0.0001); while other groups did not significantly differ. The number of grade 1 chicks in control was greater than in HYPER group. Fertility (%) was not affected by PTU or T4. In unhatched eggs, percent of non-pipping or internal pipping stage of embryonic life in HYPO was more than other groups; but external piping was not affected by treatments (P > 0.05). In conclusion, among the different reproductive parameters in this study, hatchability and weekly egg production were
the most responsive parameters to decreased or increased plasma thyroid hormone levels, respectively.