Respostas fisiológicas e termorregulação de vacas Holandês (PB) em ambiente tropical
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Data
2018-02-26
Autores
Castro, Patric André
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O estudo dos efeitos do ambiente térmico radiante sobre as respostas fisiológicas e termorregulação de animais sob diferentes ambientes em região tropical pode resultar em achados relevantes sobre a adaptação a esse meio. O presente estudo teve como objetivo investigar as respostas termorregulatórias de vacas da raça Holandesa expostas e protegidas da radiação solar direta. Foram utilizadas doze vacas Holandesas multíparas com produção média de leite de 20 kg, 676 kg de peso vivo e 120 dias de ordenha, foram distribuídas aleatoriamente em quatro quadrados latinos 6x6 sob duas condições ambientais distintas, sendo seis animais destinados a um piquete com pastagem e seis estabulados em galpão tipo Free Stall. As variáveis meteorológicas avaliadas foram temperatura do ar (TAR, °C), umidade relativa (UR, %), radiação solar (RS, W m-2 ), temperatura radiante média (TRM, °C) e velocidade do vento (VV, m s-1 ). Dados fisiológicos, incluindo frequência respiratória (FR, resp mín-1 ), ventilação (VE, L s-1 ), proporções dos gases respiratórios (oxigênio, O2; dióxido de carbono, CO2; metano, CH4), temperatura retal (TR, °C), da epiderme (TEP, °C) e temperatura superficial (TS, °C). Ao caracterizar o ambiente térmico radiante foi evidenciado que há um menor gradiente de temperatura entre TS e TRM em comparação ao gradiente entre TS e TAR mesmo em animais protegidos da radiação solar direta. A exposição das vacas a radiação solar direta influenciou na elevação das temperaturas profundas e consequentemente em maiores perdas de calor de forma sensível e latente em comparação aos animais protegidos da radiação solar, no entanto, a FR dos animais em ambos os ambientes ficaram numa faixa considerada de normalidade, entre 30,24 ± 0,45 a 40,17 ± 0,72 resp min-1 . As perdas de calor por evaporação do trato respiratório tiveram baixa representatividade no equilíbrio térmico das vacas nos dois ambientes. As perdas de calor por vias sensíveis somadas a evaporação respiratória contribuem para a dissipação de menos de 30% do calor produzido pelo metabolismo, tanto para animais protegido quanto expostos a radiação solar direta.
The study of the effects of radiant thermal environment on the physiological responses and thermoregulation of animals under different environments in a tropical region may result in relevant findings on the adaptation to this environment. This work aimed to investigate the thermoregulatory responses of Holstein cows protected and exposed to direct solar radiation. Twelve multiparous Holstein cows with average milk yield of 20 kg, 676 kg of live weight, and 120 days in milking, were randomly assigned in four 6x6 latin square design under two management system, being six subjects managed on pasture and six in housed system. The following variables were evaluated: air temperature (AT, °C), relative humidity (RH,%), solar radiation (SR, W m-2 ), mean radiant temperature (MRT, °C) and wind speed (WS, m s-1 ). Physiological data including respiratory rate (RR, breaths min-1 ), ventilation (VE, L s-1 ), proportions of respiratory gases (oxygen, O2; carbon dioxide, CO2; methane, CH4). Additionally, rectal (TR, °C), skin (TEP, °C), and hair coat surface temperature (TS, °C) were also collected. In characterizing the radiant thermal environment it was evidenced that there is a lower temperature gradient between TS and TRM compared to the gradient between TS and TAR even in animals protected from direct solar radiation. The exposure of cows to direct solar radiation influenced the elevation of deep temperatures and consequently greater heat losses in a sensitive and latent way in comparison to the protected animals of solar radiation, however, the RF of the animals in both environments were in a range considered of normal, between 30.24 ± 0.45 to 40.17 ± 0.72 resp min-1 . The evaporative heat losses of the respiratory tract had low representativeness in the thermal equilibrium of cows in both environments. Heat losses by sensible routes combined with respiratory evaporation contribute to the dissipation of less than 30% of the heat produced by metabolism, both for protected animals and exposed to direct solar radiation.
The study of the effects of radiant thermal environment on the physiological responses and thermoregulation of animals under different environments in a tropical region may result in relevant findings on the adaptation to this environment. This work aimed to investigate the thermoregulatory responses of Holstein cows protected and exposed to direct solar radiation. Twelve multiparous Holstein cows with average milk yield of 20 kg, 676 kg of live weight, and 120 days in milking, were randomly assigned in four 6x6 latin square design under two management system, being six subjects managed on pasture and six in housed system. The following variables were evaluated: air temperature (AT, °C), relative humidity (RH,%), solar radiation (SR, W m-2 ), mean radiant temperature (MRT, °C) and wind speed (WS, m s-1 ). Physiological data including respiratory rate (RR, breaths min-1 ), ventilation (VE, L s-1 ), proportions of respiratory gases (oxygen, O2; carbon dioxide, CO2; methane, CH4). Additionally, rectal (TR, °C), skin (TEP, °C), and hair coat surface temperature (TS, °C) were also collected. In characterizing the radiant thermal environment it was evidenced that there is a lower temperature gradient between TS and TRM compared to the gradient between TS and TAR even in animals protected from direct solar radiation. The exposure of cows to direct solar radiation influenced the elevation of deep temperatures and consequently greater heat losses in a sensitive and latent way in comparison to the protected animals of solar radiation, however, the RF of the animals in both environments were in a range considered of normal, between 30.24 ± 0.45 to 40.17 ± 0.72 resp min-1 . The evaporative heat losses of the respiratory tract had low representativeness in the thermal equilibrium of cows in both environments. Heat losses by sensible routes combined with respiratory evaporation contribute to the dissipation of less than 30% of the heat produced by metabolism, both for protected animals and exposed to direct solar radiation.
Descrição
Palavras-chave
Radiação solar, Conforto térmico, Taxa respiratória, Solar radiation, Thermal comfor, Respiratory rate