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Heat stress is among the most challenging environmental conditionsaffecting commercial poultry. It severely affects growth and egg production,particularly in tropical and subtropical regions. This study aimed to examinephysiological responses – including triiodothyronine (T3) levels,enzymatic activity of creatine kinase (CK) and lactate dehydrogenase (LDH),respiratory rates, and cloacal temperature – to acute heat stress associatedwith different genotypes of the HSP70 gene and to evaluate the association ofthese polymorphisms with growth and egg production. Genotyping was performedby single-strand conformation polymorphism analysis. The polymorphismsidentified were A258A, A258G, and G258G. Twenty 12-week old birds wererandomly selected from each genotype and exposed to 40 °C ambienttemperature for 1 h. Blood samples were collected at 0 and 1 h followingheat stress. Respiratory rate and cloacal temperature were measuredfollowing 0, 30, and 60 min of exposure. After 1 h, the A258A genotypeexhibited lower levels of CK activity and plasma T3. Neitherrespiratory rate nor cloacal temperature displayed a significant associationwith the genotypes. Body weight gain differed among the genotypes for males(F =  3.268, P = 0.041) and females (F =  14.029, P < 0.001),and the A258A genotype exhibited the greatest weight gain at 0–16 weeks ofage for both genders. There were no significant differences among genotypes regarding egg weightat first egg or the number of eggs laid until 40 weeks of age. The A258A genotype displayed higher heat tolerance with no negativeeffects on growth performance and egg production

Association of heat shock protein 70 gene polymorphisms with acute thermal tolerance, growth, and egg production traits of native chickens in Taiwan