Abstract
This study aimed to identify anatomical regions and developmental stages in broiler chickens that serve as reliable thermographic indicators of acute heat stress. Broilers aged 14, 21, 35, and 39 days were exposed to controlled heat stress, and surface temperatures across 12 anatomical regions were recorded using infrared thermography. Thermal response metrics (maximum, minimum, and mean peak variation) were analyzed with repeated-measures ANOVA and eta squared (η(2)) to quantify the strength of physiological responses. Principal component and cluster analyses grouped body regions based on their thermal sensitivity. The comb and wattle consistently showed the highest temperature increases (ΔT = 2.3-4.1 °C) and strongest effect sizes (η(2) ≥ 0.70), establishing them as primary thermoregulatory markers. As age increased, more body regions-especially peripheral zones like the drumstick and tail-exhibited strong responses (η(2) > 0.40), indicating an expansion of thermoregulatory activity. Cluster analysis identified three distinct sensitivity groups, confirming anatomical differences in thermal regulation. Thermographic responses to heat stress in broilers depend on age and region. The comb and wattle are the most reliable biomarkers, while peripheral responses grow more prominent with maturity. These findings support the use of targeted, age-specific infrared thermography for monitoring poultry welfare.