The effect of summer environmental conditions on the body surface temperature of growing turkeys reared outdoors

The present study aimed to determine, for the first time in turkeys, the most important body regions and environmental factors that could be used to monitor heat stress through infrared thermography imaging. To this goal, 11,093 thermal images were collected from 50 commercial toms, 23 Andalusian toms, and 27 Andalusian hens raised outdoors throughout the summer of 2022. The body areas studied included the overall head, snood, beak, dorsal body (open and closed), ventral body (open and closed), breast, underwing, and shank. Moreover, temperature, humidity, and wind variables were measured using an environmental meter device, and live weight and average daily gain were also recorded for each bird and measurement. After some variables reported non-normal distribution, a non-parametric Spearman correlation analysis was conducted to study the association between body surface and environmental variables. On the other hand, a type III ANOVA and Bonferroni-adjusted post hoc tests were performed to determine differences across the birds’ sex and genotype groups. The environmental variables most strongly correlated with body temperature were the temperature-humidity and thermal stress indices, as well as wind chill and dry bulb temperatures (p < 0.001). On the other hand, the most variable surface body temperatures were those of the shank, head, and open-dorsal areas, but varied according to the breed and sex groups. The week of measurement and the interaction between week and bird group significantly (p < 0.05) influenced all body surface variables, while bird group itself showed significant influence on specific regions. Pairwise post hoc contrasts reported significant (p < 0.05) differences between bird groups in all body surface variables, but differences were highly dependent on the week of measurement. Commercial toms had generally higher body surface temperature than Andalusian toms, while the differences in temperature with the Andalusian hens varied with the body region. Contrarily, the Andalusian toms had lower body surface temperature than females for all the variables under study. Therefore, the higher body surface temperature of the commercial toms, together with their greater influence of environmental events, highlights the greater adaptability of the Andalusian turkeys to free-range, uncontrolled weather conditions compared to specialized strains.