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A adaptação dos animais ao ambiente criatório é essencial para o êxito de qualquer empreendimento pecuário. No Brasil, há algumas décadas, foram importadas inúmeras raças, oriundas de clima temperado, das mais diversas espécies de animais de produção, cujas progênies eram avaliadas e selecionadas em consideração apenas dos aspectos produtivos. Nos últimos dez anos, verificou-se que tanto criadores, como a comunidade acadêmica, despertaram para a valorização de aspectos adaptativos, ao selecionarem animais a serem criados nos mais diversos biomas brasileiros. Observa-se, assim, a valorização das raças nativas de pequenos ruminantes e zebuínos para a exploração de carne e leite. No entanto, avaliar e selecionar animais pelas características adaptativas requer uma padronização de parâmetros e metodologias para a colheita de dados confiáveis. Ao se considerar que a homeostase representa a condição de equilíbrio em um sistema biológico e que animais adaptados ao ambiente exibem claros sinais de homeostasia, procurou-se, neste trabalho, abordar uma metodologia fundamentada numa matriz multifatorial para avaliar a adaptação, na qual são consideradas as reações termorreguladoras, como forma de manter a homeotermia, indicadas pelas temperaturas retal e de superfície, acionamento da termólise evaporativa, representadas pela frequência respiratória e taxa de sudação. Para avaliação da homeostase recomenda-se a associação de reações endócrinas, tais como níveis circulantes de hormônios da tireoide e cortisol, aos parâmetros bioquímicos dentro da faixa de normalidade. Todos esses fatores, em equilíbrio, permitem aos animais expressar satisfatoriamente as funções reprodutiva e produtiva.

Semi-arid conditions can adversely affect livestock productivity and change certain physiological parameters. The relationship between hair coat and thyroxine levels in Morada Nova ewes was evaluated through environmental factors, such as air temperature, relative air humidity, radiant and Black Globe Humidity Index to gain a better understanding of thermoregulation mechanisms in these animals. Measurements were taken from July to January in 383 Morada Nova ewes. The variables studied included rectal temperature (RT), respiratory rate (RR), coat thickness (CT), hair length (HL), hair diameter (HD), hair density (D) and thyroid hormones. The data underwent multivariate statistical analyses and a significant inverse relationship was found between coat traits and Thyroxine (T 4 ). The animals that exhibited greater HL, coat density and CT showed lower T 4 concentrations. Coat traits showed a strong interaction with physiological mechanisms and can be considered relevant in maintaining homeostasis. Hair traits play an important role in this process, since T 4 reduction was stronger in animals that showed difficulties in eliminating heat, which were the ones that had greater HL, hair density and HD. By contrast, animals with a hair coat more favourable to heat losses had higher levels of thyroid hormones. ARTICLE HISTORY

The goal of this study was to evaluate the daily rhythmicity of the thermoregulatory responses of Morada Nova ewes that were raised in a semiarid environment. The experiment was conducted during the dry season. Data were collected from 5:00 a.m. to 4:00 a.m.. Samples were taken over the course of 8 days, with a 1-week interval between sampling periods. During each day that the data were collected, animals were measured once an hour for 24 h in an area directly exposed to solar radiation. The environment was characterized by measuring the following variables: air temperature (TA), relative humidity (RH), Black Globe Humidity Index (BGHI), radiant heat load (RHL), and wind speed (WS). Physiological variables that were measured included rectal temperature (RT, °C), respiratory rate (RR, breaths/min), surface temperature (ST, °C), and sweating rate (SR, g m h). We observed that RT, RR, and ST increased as environmental conditions became more stressful. Specifically, environmental conditions became more stressful as RHL, air temperature, and BGHI increased, while RH decreased. All physiological variables of the animals were strongly affected by the time of the day: environmental variables changed drastically between nighttime and noon. Physiological parameters increased sharply from the morning (7:00 a.m.-10:00 a.m.) until noon (11:00 a.m.-2:00 p.m.), except for sweating rate. After noon, these variables began to drop until nighttime (11:00 p.m.-6:00 am), and values of the main physiological indexes were stable during this period. The Morada Nova breed exhibited daily cyclic variations in thermoregulatory responses. Evaporative heat loss mechanisms were triggered during the most stressful times of the day. The first mechanism that animals used was panting, which was an immediate response to environmental heat stress. Cutaneous evaporation had a slower response mechanism to environmental heat stress. Homeothermy conditions were restored to the animals at approximately 5:00 p.m.; however, these findings confirm the importance of providing environmental protection during critical periods of the day, even for locally adapted breeds. These responses suggest that the use of thermal storage allowed the animals to achieve equilibrium with the environment and maintain a stable body temperature.

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