Abstract: 【Objective】 To investigate the effects of exogenous triiodothyronine (T3) on development and deiodinases expression during late-term embryonic and early post-hatch development in newly hatched Jinding ducks, we injected fertile eggs with T3 or vehicle before incubation, observed the changes of body weight and the weight of pectoralis major (PM) in prenatally T3-exposed ducks, and analyzed serum thyroid hormones level as well as the mRNA expression, the protein level, and the activity of deiodinases I (D1) deiodinases Ⅲ (D3) in liver. 【Method】Two hundreds fertile Jinding breeder eggs were randomly divided into two groups and injected with 0 ng (the control group) or 250 ng (the treatment group) of T3 in 100 µL of normal saline from the sharp of eggs before incubation. All the eggs were hatched at the same time and under the same conditions. Body weights and the weight of PM were recorded, meanwhile. Serum T3 and T4 levels were detected by Radioimmunoassay (RIA), deiodinases mRNA expressions were evaluated by Real-time fluorescent quantitative PCR (RT-QPCR), deiodinases protein content as well as the activity in liver were evaluated by Enzyme-Linked Immunosorbent Assay (ELISA) at the embryonic day 27 and the age of 7 days. 【Result】The results showed that body weights (P = 0.035, 0.044) and the weight of PM (P = 0.027, 0.037) in the treatment group were higher than that in the control group on the embryonic day 27 and the age of 7 days. There were no significant difference in serum T3 and T4 levels between the treatment group and the control group on the embryonic day 27 (P＞0.05), but they were all declined compared with the control group at the age of 7 days (P = 0.040, 0.040). The protein content and the activity of D1 (P = 0.017, 0.013) and D3 (P = 0.045, 0.039) as well as D3 mRNA expression (P = 0.040) in liver were all down-regulated compared with the control group at the age of 7 days. There was a significantly negative linear correlation between serum T3 level and the weight of PM during late-term embryonic and early post-hatch development (r = -0.431, P = 0.025), T3 level and D3 mRNA expression in liver was significantly positive correlated (r = 0.778, P = 0.005), but there was also a significantly positive linear correlation between T4 level and D1 protein, D1 activity, D3 protein, and D3 activity (r = 0.685, P = 0.020; r = 0.662, P = 0.026; r = 0.710, P = 0.014; r = 0.705, P = 0.015). 【Conclusion】These results suggested that in ovo T3 administration promoted the ducks’ development during perinatal period, meanwhile, along with the decline of circulating THs level and the down-regulation of D1 and D3 expression in liver after incubation.

Key words: duck, T3, early development, D1, D3, gene expression, enzyme activity