Thermal radiation absorbed by dairy cows in pasture
2010
da Silva, Roberto Gomes | Guilhermino, Magda Maria | de Morais, Débora Andréia E Façanha
The goal of the present paper was to assess a method for estimating the thermal radiation absorbed by dairy cows (0.875 Holstein-0.125 Guzerath) on pasture. A field test was conducted with 472 crossbred dairy cows in three locations of a tropical region. The following environmental data were collected: air temperature, partial vapour pressure, wind speed, black globe temperature, ground surface temperature and solar radiation. Average total radiation absorbed by animals was calculated as [graphic removed] . Absorbed short-wave radiation (solar direct, diffuse and reflected) averaged 297.9 ± 2.7 W m⁻²; long wave (from the sky and from terrestrial surfaces) averaged 342.1 ± 1.5 W m⁻². It was suggested that a new environmental measurement, the effective radiant heat load (ERHL), could be used to assess the effective mean radiant temperature [graphic removed] . Average [graphic removed] was 101.4 ± 1.2°C, in contrast to the usual mean radiant temperature, [graphic removed] . Estimates of [graphic removed] were considered as more reliable than those of T mr in evaluating the thermal environment in the open field, because T mr is almost totally associated only with long wave radiation.
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