Integração entre parâmetros fisiológicos e morfológicos como indicadores de adaptação térmica em caprinos nativos do semiárido

Abstract

Goat farming is a growing activity in Northeast Brazil, supported by the hardiness of goats and their ability to adapt to the harsh conditions of the semi-arid region. However, these animals are exposed to environmental stressors related to heat, nutritional restriction, and water deficit, which directly affect their productive performance and well-being. The objective was to evaluate physiological responses, coat and skin characteristics, and renal morphology of Canindé and Moxotó goats subjected to energy supplementation during the dry season in the Caatinga biome. Forty castrated male goats were used, 20 of the Canindé breed and 20 of the Moxotó breed, distributed in a completely randomized design, in a 2 × 2 factorial arrangement (breed × supplementation: 0% and 1% of body weight), from December 2023 to March 2024. The monitored environmental variables (air temperature, relative humidity, wind speed, black globe temperature in sun and shade, and Temperature-Humidity Index (THI)) confirmed thermal stress conditions. Physiological parameters were evaluated: respiratory rate (RR), rectal temperature (RT), and surface temperature (ST); in the coat, thickness (TP), length (LL), density, and diameter of the hairs; in the skin, epidermal thickness (EPT), blood capillary area (ACSAN), and sweat gland area (AGSUD) in three body regions (shoulder, rib, and leg); In the kidneys, the distribution of cortical and juxtamedullary nephrons was also analyzed. The results showed that the Canindé breed presented higher respiratory rate (RR) (80.7 breaths/min−1) and bath time (BT) (38.7 °C) compared to the Moxotó breed (62.7 breaths/min−1; 37.5 °C), while rectal temperature remained within the physiological range for the species. In the coat, there was no effect of supplementation, but there were differences between breeds: the Moxotó breed presented a higher epidermal profile (5.22 mm), while the Canindé breed presented a higher coat circumference (CC) (34.7 mm). In the skin, there was a breed effect on the ACSAN (area of skin tissue and urea nitrogen), with a higher value in the Moxotó breed (148.03 μm cm−2). Supplementation positively influenced (P < 0.05) EEP (54.75 μm), ACSAN (156.09 μm cm−2) and AGSUD (273.75 μm cm−2). Among body regions, the shoulder presented the highest EEP (59.77 μm), followed by the rib (50.16 μm) and ham (42.34 μm), and the highest ACSAN values (shoulder 153.11 μm cm−2; rib 154.03 μm cm−2; ham 115.04 μm cm−2). In renal morphology, there was no difference between breeds in the number of nephrons, but both showed a greater number of cortical nephrons compared to juxtamedullary nephrons. The latter are characteristic of animals adapted to regions with water deficits and are fundamental for urinary concentration and survival in semi-arid environments. It is concluded that Canindé and Moxotó utilize different adaptive mechanisms, with Moxotó being more efficient due to the structure of its coat and skin, and that energy supplementation enhances morphophysiological thermoregulation mechanisms in both breeds.