Thermal radiation absorbed by dairy cows in pasture

Abstract

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.

Thermoregulatory responses and blood parameters of locally adapted ewes under natural weather conditions of Brazilian semiarid region

“…The BGHI and the Radiant Heat Load (RHL) were always high, confirming the chronic stressful environment, according to Silva et al (2010). The average wind speed were low throughout the year (VAREJÃO-SILVA, 2001).…”

“…It is important clarify that the low latitude regions are characterized by high air temperatures and levels of solar radiation during all the year (SILVA et al, 2010). The mean environmental temperature varies from 25 °C to 35 °C, and the relative air humidity is approximately 70%.…”

“…The data were analyzed by the least-squares method (SAS, 2010), adopting a repeated measurement design, following the technical program pointed by Façanha et al (2010). The linear model used was: Y ijk = μ + V i + S j + VS ij + CBCS k + e ijk , where: Y ijk = the parameter of interest; μ = overall mean for the parameter of interest; V i = fixed effect of variety (white or red); S j = effect of season during collection; VS ij = interaction effect of variety and season; CBCS k = effect of class of body condition score; e ijk = Random error.…”

“…However, when these mechanisms fail, the RT increases, leading to hyperthermia (MARAI et al, 2007). In fact, animals have different ways to control internal temperature; in ruminants, especially those raised under field conditions in tropical areas, the respiratory and cutaneous thermolysis are the only way to dissipate heat when the air temperature exceeds the body surface temperature (SILVA et al, 2010).…”

Physiological parameters, hair coat morphological characteristics and temperature gradients in holstein-gyr crossbred cows

“…Changes in the respiratory rate and rectal temperature are related to the physiological response to stress (COSTA;SILVA et al, 2009). These parameters may be used to assess thermal comfort and other characteristics of an animal's outer shell, specifically its thickness, structure and thermal insulation properties, in addition to other environmental factors, including solar radiation, atmospheric pressure, temperature and relative humidity (SILVA, 2000).…”