Effect of Thermal Stress on Thermoregulation, Hematological and Hormonal Characteristics of Caracu Beef Cattle

SIMPLE SUMMARY: Heat stress impacts animal production, reproduction, health, and welfare, making it profitable to raise animals adapted to the climate. In this context, Caracu (Bos taurus taurus) is the large Creole breed adapted to the Brazilian tropical climate. Thus, this study investigated the influence of environmental temperature on thermoregulation (surface temperature obtained by infrared thermography and rectal temperature), hormonal (cortisol, cortisone, and progesterone), and hematological characteristics of Caracu. The results revealed that heat stress changes several physiological characteristics of Caracu cattle, although most of them remained within the regular values observed for taurine Creole breeds. In addition, males and females exhibited differences in their responses to heat stress. The decrease in animal production caused by heat stress is a growing concern. Therefore, the identification and wide use of naturally resistant animals in terminal crossbreeding schemes to explore heterosis and complementarity, and in pure herds, is important to minimize the impact of heat stress on animal production. ABSTRACT: This study evaluated the influence of environmental temperature on thermoregulation, hormonal, and hematological characteristics in Caracu cattle. Blood samples, hair length, coat and muzzle colors, rectal (RT), and surface temperatures were collected from 48 males and 43 females before (morning) and after sun exposure for eight hours (afternoon). Infrared thermography (IRT) was used to identify superficial temperature that exhibits a high correlation with RT. Hematological parameters, hormone concentrations, RT, and the superficial temperature obtained by IRT that exhibited the highest correlation with RT were evaluated by variance analysis. Regarding IRT, the lower left side of the body (LS) showed the highest correlation with the RT. Interaction between period and sex was observed for LS, cortisol, and eosinophils. Cortisone, progesterone, and RT were influenced by period and sex. Neutrophils and segmented neutrophils were influenced by the period, which showed the highest concentrations after sun exposure. Platelets, leukocytes, lymphocytes, and monocytes were influenced by sex. Heat stress changes several physiological characteristics where males and females exhibited differences in their responses to heat stress. Furthermore, most characteristics evaluated remained within the regular values observed for taurine Creole breeds, showing that Caracu is adapted to tropical climates.