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Effect of the radiant thermal environment on physiological responses of Holstein cows in tropical environment

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Patric André Castro
Total Authors: 1
Document type: Master's Dissertation
Press: Jaboticabal. 2018-04-25.
Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências Agrárias e Veterinárias. Jaboticabal
Defense date:
Advisor: Alex Sandro Campos Maia; Vinícius de França Carvalho Fonseca

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. (AU)

FAPESP's process: 16/11810-1 - Methane emissions (CH4) enteric associated with physiological responses of Holstein cows under different management systems
Grantee:Patric André Castro
Support type: Scholarships in Brazil - Master