Acute Thermal Tolerance and Physiological Responses in Commercial and Native Red-Feathered Roosters Sharing the Same HSP70 Homozygous Genotype

Taiwan’s subtropical climate poses substantial heat stress challenges to poultry production. This study compared four red-feathered rooster lines (n = 10 per line, BB homozygous HSP70 genotype)—three commercially bred lines (F, T, K) selected for maximum body weight, and one native trial line (TLRI-09) developed through marker-assisted selection targeting the HSP70 BB genotype—during a one-hour acute heat challenge at 42 °C. A pre-specified statistical decision tree was applied: normality was assessed by the Shapiro–Wilk test for each group’s change score (Δ = post − pre); one-way ANOVA with Tukey’s HSD was used when all groups were normally distributed; Kruskal–Wallis with Dunn’s post hoc test (Bonferroni correction) was used otherwise. Within-group pre-to-post changes were assessed by paired t-test. TLRI-09 showed a substantially lower body weight (909 ± 102 g vs. 2039–2226 g) and zero mortality, whereas each commercial line experienced one death (10%). Cloacal temperatures in F, T, and K groups exceeded the thermometer’s upper limit (>44 °C) within one hour; TLRI-09 reached only 42.8 ± 0.1 °C. Respiratory rate increment was highest in TLRI-09 (Δ = 82.0 ± 8.4 breaths/min) and differed significantly among lines (p < 0.001). Plasma T3 change differed among lines (p = 0.006); post hoc analysis identified a significant K vs. T contrast only (p = 0.019). These results indicate that, despite sharing the same HSP70 genotype, breeding objective is an important determinant of acute thermal resilience—an observation that warrants further validation under chronic and commercial production conditions.