Abstract

Early-life thermal conditioning (TC) in broiler chickens has long-lasting impacts on later life. Therefore, this study aimed to clarify the molecular mechanism by which TC impacts the hepatic expression heat shock proteins (hsps), antioxidant enzymes, NADPH oxidase 4 (NOX4), glucocorticoid receptor (GR), and DNA methyltransferases genes in broiler chicks at five weeks of age. Two hundred forty one-day-old male broiler chicks of Cobb 500 were allocated into four equal experimental groups. The first group was under the optimal brooding conditions (control), whereas the 2^nd, 3^rd, and 4^th groups were exposed to TC at 39 ± 1 °C for six hours on the third-, fifth- or seventh-day post-hatch, respectively. At 35 days of age, all chicks of four experimental groups were subjected to heat challenge by exposure to 36 ± 1 °C for six hours. Results showed that broilers exposed to TC on the fifth-day post-hatch when exposed to acute heat stress at five weeks of age had the lowest plasma CORT level, the lowest expression (p < .05) for NOX4, GR, SOD, SOD2, and CAT among all groups. The same trend was observed for hsp70, hsp90A, hsp90B, hsp60, and hspA9. In conclusion, early thermal conditioning on the fifth-day post-hatch may improve thermotolerance by decreasing NOX4 and GR expressions, leading to reduced heat shock proteins and antioxidant enzyme gene expression subsequently reduced oxidative stress.

• Highlights

• Thermal conditioning is a promising approach to mitigate heat stress in broiler chicks.

• The optimal age to perform thermal conditioning is a controversial issue.

• Heat shock proteins gene expression and plasma corticosterone are good indicators for thermotolerance acquisition.

• Thermal conditioning on the fifth-day post-hatch reduced oxidative stress at five weeks of age.

摘要

肉鸡的早期生命调节（TC）对以后的生命具有长期影响。因此，本研究旨在阐明TC影响五周龄肉鸡肝脏表达热休克蛋白（hsps），抗氧化酶，NADPH氧化酶4（NOX4），糖皮质激素受体（GR）和DNA甲基转移酶基因的分子机制。年龄。将240只一天大的Cobb 500雄性肉鸡雏鸡分为四个相等的实验组。第一组是最佳的育雏条件（对照）下，而2^次，3^次和4^次分别在孵化后第三天，第五天或第七天，将各组分别于39±1°C的温度下暴露6小时。在35天大时，四个实验组的所有小鸡都通过暴露于36±1°C六个小时而受到热刺激。结果显示，在孵化后第五天暴露于五周龄的急性热应激时暴露于TC的肉鸡的血浆CORT水平最低 ，NOX4，GR，SOD和SOD2的最低表达（p <.05）。，以及所有组中的CAT。对于hsp70，hsp90A，hsp90B，hsp60和hspA9，观察到相同的趋势。总之，在孵化后第五天进行早期热调节可以通过降低NOX4和GR表达来提高耐热性，从而导致热休克蛋白和抗氧化酶基因表达降低，进而降低氧化应激。

• 强调

• 热调节是减轻肉鸡热应激的一种有前途的方法。

• 进行热调节的最佳年龄是一个有争议的问题。

• 热休克蛋白基因表达和血浆皮质酮是耐热性获得的良好指标。

• 孵化后第五天进行热调节可降低五周龄的氧化应激。