Estimativa do Balanço Térmico por Radiação em Vacas Holandesas Expostas ao Sol e à Sombra em Ambiente Tropical

Abstract

A method is presented to estimate the radiation heat balance of Holstein cows exposed to sun and under shade of a pasture, to contribute with a morphological characteristics better adequate for these animals in a tropical environment. The methods involved the haircoat characteristics (surface area of black spots, coat thickness, hair length, hair diameter, number of hairs per unit of area), skin and coat surface temperatures and environmental variables (solar irradiance, wind speed, air and globe temperatures). The amount of shortwave energy which effectively is transmitted through the haircoat and that reach deply the epiderms layers was obtained. It was demonstrated by a practical example that the black areas of the coat presented higher radiation heat balance than that of the white areas, but those had greater transmissivity for shortwave radiation. Predominantly black cows were better protected against shortwave radiation than the white ones, especially if the animals presented thin (4 to 7 mm or less) haircoats, the most suitable for tropical environments.