Thermal radiation absorbed by dairy cows in pasture
Tóm tắt
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
$$ {R_{abs}} = 640.0 \pm 3.1\, W.{m^{ - 2}} $$
. 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
$$ \left( {T_{\text{mr}}^* } \right) $$
. Average
$$ T_{\text{mr}}^* $$
was 101.4 ± 1.2°C, in contrast to the usual mean radiant temperature,
$$ {T_{mr}} = 65.1 \pm 0.5^\circ C $$
. Estimates of
$$ T_{\text{mr}}^* $$
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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