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Not Availablehe present experiment was conducted to evaluate the Hsp-70, 27 and Ubiquitin mRNA expressions and serum T3 concentration in synthetic colored broiler female lines, Punjab Broiler-2 (PB-2), and Naked neck (NN) broiler chicken whose eggs were exposed to 2°C increased incubation temperature for 3 hours each on the 16th, 17 th, and 18th day of incubation. Another set of eggs were incubated at normal conditions that were utilized as the control. A total of 432 chicks, 216 from each breed (PB-2; NN) and treatment (Heat exposed: HE; normal: N), were randomly distributed and reared at high ambient temperatures (32°C-45°C) during the summer season in battery brooders. Birds were sacrificed at 0 and the 28th day post hatch and different tissues (heart, liver, muscle, spleen, and bursa) were collected to study Hsps and ubiquitin mRNA expression. There was no difference between the breeds and age of slaughter in Hsp-70 mRNA expression. The Hsp(70, 27, and ubiquitin) mRNA expression was significantly (P≤0.001) lower in HE birds than that of N birds in PB-2 chickens. Nonsignificant variation was observed in NN chicken. The Hsp-70 mRNA expression was highest in bursa and lowest in muscle and liver. Serum T3 concentration was similar in both HE and N birds. The study concludes that exposure to increased temperature during incubation results in reduced expressions of Hsp mRNA in almost all tissues indicating better thermotolerance of the HE birds.ICAR-NICR