Estudo do equilíbrio térmico associado à emissão de CH4 em bovinos Nelore manejados a campo durante o período de 24 horas
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Data
2018-02-26
Autores
Costa, Cíntia Carol de Melo [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Diante do cenário climático global atual se torna importante entender quais os impactos de uma atmosfera aquecida sobre o equilíbrio térmico em animais de produção, especialmente em bovinos. A quantificação da emissão de gases do efeito estufa desses animais também se faz importante, pois apesar dessa atividade ter impacto positivo na economia nacional, do ponto de vista ambiental o seu impacto é negativo, devido ao fato da fermentação entérica contribuir com emissões de metano. Portanto, o objetivo desse estudo é avaliar a influência das condições meteorológicas sobre a termorregulação de bovinos da raça Nelore associada à emissão de metano durante o período circadiano. Para tanto, foi realizado estudo no Laboratório de Biometeorologia Animal da Universidade Estadual Paulista, Jaboticabal, Brasil, em Dezembro de 2016. Seis bovinos da raça Nelore com peso e idade semelhantes foram avaliados em um desenho experimental de quadrado latino, com 24 classes de horas (1-2h; 3-4h; …; 23 - 24h; 24 -1h) durante vinte dias consecutivos). As coletas de dados foram realizadas com os animais protegidos da radiação solar e chuva. Os parâmetros respiratórios: porcentagem de oxigenio (O2; %), dióxido de carbono (CO2; %), metano entérico (CH4, %) pressão de vapor do ar expirado ([PS{TEXP}, kPa), frequência respiratória (RR; resp. min-1) e ventilação (VE; L s-1) foram quantificados usando o sistema de calorimetria indireta; além disso, a temperatura da superfície (TS, °C), pele (TEP, °C) e temperatura retal (TR, °C) foram medidas usando sensores de temperatura. A produção de calor metabólico (q”met), fluxo de calor sensível (q”sens), perda de calor pelo trato respiratório (q”er), evaporação cutânea (q”es) e emissão de metano entérico (eCH4; g h-1) foram calculados. As variáveis meteorológicas foram medidas em intervalos de um minuto durante cada dia de coleta usando uma estação meteorológica portátil. Os volumes de O2 e CO2 mudaram moderadamente durante as 24 horas, o que resultou em uma média de produção de calor metabólico de 151,45 ± 13,60 W m-2. Quando o gradiente de temperatura estava alto (TS – TA; das 24:00 às 7:00), a transferência de calor sensível correspondeu a aproximadamente 60% do metabolismo, porém das 11:00 até às 17:00, quando a temperatura do ar estava mais elevada, a perda de calor por evaporação cutânea passa a representar cerca de 53% da perda de calor total. As respostas fisiológicas termorreguladoras de bovinos Nelore, em uma variação de 20 a 30°C de TA, permanecem relativamente estáveis durante 24 horas, sendo um bom indicativo de baixa perda de energia para regulação térmica corporal. A emissão de metano de bovinos Nelore confinados, com 30 meses de idade, alimentados para mantença, foi de aproximadamente 33 g dia-1 animal-1. A variação circadiana de metano entérico (CH4) foi claramente associada ao horário de alimentação, não estando relacionada a variação meteorológica. O circuito aberto de calorimetria indireta, usando uma máscara facial não ventilada propicia valiosos detalhes sobre o padrão diário da emissão de metano de bovinos Nelore, associado com o O2 consumido e CO2 produzido. Portanto este trabalho foi capaz de avaliar o equilíbrio térmico de bovinos Nelore adultos, além descrever a variação circadiana de emissão de metano, bem como a relação dessas variáveis com as condições meteorológicas de ambiente tropical. Com isso, este trabalho traz contribuições altamente relevantes para a área, com resultados inéditos e inovações.
Given the current global climate scenario becomes important to understand what the impacts of a warmer atmosphere on the thermal balance in livestock. Quantifying the emission of greenhouse gases of these animals also becomes important because this activity has a positive impact on the national economy, however, the environmental point of view the impact is negative, because of the contribution of methane emission by enteric fermentation. Therefore, the aim of this work is study the influence of meteorological condition on thermoregulation of Nellore cattle associated with the emission of methane throughout the day. For this, it was done a study at the Animal Biometeorology Laboratory of the São Paulo State University, Jaboticabal, Brazil (21.25° S, 601 m altitude) in December of 2016. Six Nellore cattle with similar weight, age and body condition were assigned in a Latin Square experimental design (24 classes of hours (1-2h; 3-4h; …; 23 - 24h; 24 -1h) during twelve days). Evaluations were performed with animals protected from direct solar radiation and rain overnight. Respiratory parameters as percentage of oxygen (O2; %), carbon dioxide (CO2; %), methane emission (CH4, %), water vapor pressure (PS{TEXP}; kPa), respiratory rate (RR, breaths min-1 ) and ventilation (VE; L s -1 ) were quantified using an indirect calorimetry system; furthermore, hair coat surface (TS, °C), skin (TEP, °C) and rectal temperature (TR, °C) were recorded with thermocouple. Metabolic heat production (q”met), sensible heat flow (q”sens), heat loss from respiratory tract (q”er) and cutaneous evaporation (q”es) and methane emission (eCH4, g h-1 ) were calculated. Meteorological conditions were measure at regular one-minute intervals during each day with a portable weather station. Volumes (L h - 1 ) of O2 and CO2 changed moderately throughout the 24 hours, which resulted in an average metabolic heat production of 151.45 ± 13.60 W m-2 . At the largest thermal gradient (TS - TA; from 24:00 h to 7:00 h), heat transferred by sensible mechanisms corresponded near to 60 % of the metabolism, but at 11:00 h until 17:00 h, when TA was elevated, the cutaneous evaporation represented approximately 53 % of total heat losses. From 20 to 30 °C, thermoregulatory responses of Nellore cattle remained relatively stable over the 24 hours when protected from direct solar radiation and rain, which seems to be a good indicative of lower energy expenditure for body thermal regulation. Enteric methane emission of housed 30-mo-old Nellore cattle fed at requirement maintenance on DM basis is approximately 33 g day-1 animal-1 . Circadian variation of enteric methane emission was clearly associated to the feed time, being not related with meteorological conditions. The open indirect calorimetry system using a non-ventilated facial device provided valuable details on daily pattern of enteric CH4 production of Nellore cattle and its association with O2 consumption and CO2 output. So, this work evaluated the thermal equilibrium of adult Nellore cattle, besides to describe the circadian variation of methane emission, as well as the relationship of these variables with tropical meteorological conditions. Thereby, this work has relevant contributions with inedit results and inovation.
Given the current global climate scenario becomes important to understand what the impacts of a warmer atmosphere on the thermal balance in livestock. Quantifying the emission of greenhouse gases of these animals also becomes important because this activity has a positive impact on the national economy, however, the environmental point of view the impact is negative, because of the contribution of methane emission by enteric fermentation. Therefore, the aim of this work is study the influence of meteorological condition on thermoregulation of Nellore cattle associated with the emission of methane throughout the day. For this, it was done a study at the Animal Biometeorology Laboratory of the São Paulo State University, Jaboticabal, Brazil (21.25° S, 601 m altitude) in December of 2016. Six Nellore cattle with similar weight, age and body condition were assigned in a Latin Square experimental design (24 classes of hours (1-2h; 3-4h; …; 23 - 24h; 24 -1h) during twelve days). Evaluations were performed with animals protected from direct solar radiation and rain overnight. Respiratory parameters as percentage of oxygen (O2; %), carbon dioxide (CO2; %), methane emission (CH4, %), water vapor pressure (PS{TEXP}; kPa), respiratory rate (RR, breaths min-1 ) and ventilation (VE; L s -1 ) were quantified using an indirect calorimetry system; furthermore, hair coat surface (TS, °C), skin (TEP, °C) and rectal temperature (TR, °C) were recorded with thermocouple. Metabolic heat production (q”met), sensible heat flow (q”sens), heat loss from respiratory tract (q”er) and cutaneous evaporation (q”es) and methane emission (eCH4, g h-1 ) were calculated. Meteorological conditions were measure at regular one-minute intervals during each day with a portable weather station. Volumes (L h - 1 ) of O2 and CO2 changed moderately throughout the 24 hours, which resulted in an average metabolic heat production of 151.45 ± 13.60 W m-2 . At the largest thermal gradient (TS - TA; from 24:00 h to 7:00 h), heat transferred by sensible mechanisms corresponded near to 60 % of the metabolism, but at 11:00 h until 17:00 h, when TA was elevated, the cutaneous evaporation represented approximately 53 % of total heat losses. From 20 to 30 °C, thermoregulatory responses of Nellore cattle remained relatively stable over the 24 hours when protected from direct solar radiation and rain, which seems to be a good indicative of lower energy expenditure for body thermal regulation. Enteric methane emission of housed 30-mo-old Nellore cattle fed at requirement maintenance on DM basis is approximately 33 g day-1 animal-1 . Circadian variation of enteric methane emission was clearly associated to the feed time, being not related with meteorological conditions. The open indirect calorimetry system using a non-ventilated facial device provided valuable details on daily pattern of enteric CH4 production of Nellore cattle and its association with O2 consumption and CO2 output. So, this work evaluated the thermal equilibrium of adult Nellore cattle, besides to describe the circadian variation of methane emission, as well as the relationship of these variables with tropical meteorological conditions. Thereby, this work has relevant contributions with inedit results and inovation.
Descrição
Palavras-chave
Balanço térmico, Bovinos de corte, calorimetria indireta, termorregulação, emissão de metano, Thermal balance, beef cattle, indirect calorimetry system, thermoregulation, methane emission