Sensible and latent heat loss from the body surface of Holstein cows in a tropical environment.
The general principles of the mechanisms of heat transfer are well known, but knowledge of the transition between evaporative and non-evaporative heat loss by Holstein cows in field conditions must be improved, especially for low-latitude environments. With this aim 15 Holstein cows managed in open pasture were observed in a tropical region. The latent heat loss from the body surface of the animals was measured by means of a ventilated capsule, while convective heat transfer was estimated by the theory of convection from a horizontal cylinder and by the long-wave radiation exchange based on the Stefan-Boltzmann law. When the air temperature was between 10 and 36 degrees C the sensible heat transfer varied from 160 to -30 W m(-2), while the latent heat loss by cutaneous evaporation increased from 30 to 350 W m(-2). Heat loss by cutaneous evaporation accounted for 20-30% of the total heat loss when air temperatures ranged from 10 to 20 degrees C. At air temperatures >30 degrees C cutaneous evaporation becomes the main avenue of heat loss, accounting for approximately 85% of the total heat loss, while the rest is lost by respiratory evaporation.
Maia
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Laboratory of Bioclimatology, Department of Animal Science, College of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal Campus, Via Paulo Donato Castellane, km. 5, 14884-900 Jaboticabal, São Paulo, Brazil. alexsan@fcav.unesp.br
daSilva
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Battiston Loureiro
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D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D001938:Brazil; D002417:Cattle / Q000502:physiology*; D005260:Female; D006813:Humidity; D008954:Models, Biological; D012879:Skin Physiological Phenomena; D013696:Temperature; D014329:Tropical Climate