The 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.

The mRNA expression profiles of Hsp-90 alpha, Hsp-90 beta and Hsp-60 were evaluated in coloured broiler chickens, that is, Punjab broiler-2 (PB-2) and naked neck (NN), exposed to 2°C increased incubation temperature for 3 h each on 16th, 17th and 18th days of incubation. Another set of eggs were incubated at normal conditions that were utilized as control. A total of 432 chicks, 216 in each breed (PB-2; NN) and treatment (heat exposed; normal), randomly distributed were reared at high ambient temperatures (32–45°C) during summer in battery brooders. Birds were sacrificed on 0 and 28th days post-hatch and different tissues (heart, liver, muscle, spleen and bursa) were collected to assess the mRNA expression. Heat exposure during incubation significantly (P ≤ .05) influenced the expression of Hsp-90 alpha in spleen of day old; in heart, liver and spleen at 28 days in PB-2 chicken. Hsp-90 alpha mRNA expression was not significant among the tissues at different ages in NN chicken. Hsp-90 beta did not show any significant variations in gene expression across the tissues at both the age groups either in NN or in PB-2 chicken. Heat exposure had significant effect in the expression patterns of Hsp-60 at 28 days in heart, liver and spleen in PB-2 chicken. The mRNA expression of all the three genes significantly (P ≤ .05) varied in different tissues across the age groups in both PB-2 and NN chickens. The study concluded that thermal adaptation during the embryonic stage to higher incubation temperature reduced Hsp gene expression in different tissues in postnatal life during high ambient temperature which might result in increased heat tolerance capacity of the broiler chickens.