Thermal radiation absorbed by dairy cows in pasture.
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 +/- 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 (T*(mr)). Average T*(mr) was 101.4 +/- 1.2 degrees C, in contrast to the usual mean radiant temperature, T(mr) = 65.1 +/- 0.5 degrees C. Estimates of T*(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.
da Silva
Roberto Gomes
RG
Departamento de Ciência Animal, Universidade Federal Rural do Semi-Arido, Mossoró, RN, Brazil. robertogs@terra.com.br
Guilhermino
Magda Maria
MM
de Morais
Débora Andréia E Façanha
DA
D000818:Animals; D001681:Biological Assay / Q000379:methods; D001833:Body Temperature Regulation / Q000502:physiology* / Q000528:radiation effects*; D002417:Cattle / Q000502:physiology*; D003198:Computer Simulation; D004781:Environmental Exposure / Q000032:analysis*; D006358:Hot Temperature; D008954:Models, Biological; D012062:Relative Biological Effectiveness; D012993:Solar Energy; D014915:Whole-Body Counting / Q000379:methods*; D014919:Wind