Absorption of Radiation by Different Coat Patterns of Crossbred Sheep

Abstract

The objective of this study was to quantify the heat load from shortwave radiation by crossbred sheep with different coat patterns in a pasture-based system without shade. Nine crossbred sheep with white, brown and black coats without access to shade were evaluated. The research was conducted at the Iguatemi Experimental Farm, which belongs to the State University of Maringá. The physiological parameters collected were the respiratory rate and surface temperature of the animals. The meteorological parameters were temperature (ºC) and relative humidity of air (%) and solar radiation (Wm^-2). The heat load from shortwave radiation was quantified based on the components of direct, diffuse and reflected radiation and considering the absorptance of the sheep's coat. The data were analyzed by the least squares method and the unfolding of the means by the Tukey test at 5%. The air temperature ranged from 30.2°C to 41°C, and the relative humidity had an average of 63%; while solar radiation exceeded 1100Wm^-2. Heat load differed significantly between coats (P<0.05), with black, brown and white animals absorbing on average 1037, 600 and 460Wm^-2, respectively. Black and brown animals had an average respiratory rate of 119breaths.min^-1, differing (P<0.05) from white animals with 109breaths.min^-1. Therefore, animals with brown coat are better adapted to tropical environments, as they have greater skin pigmentation than white animals and absorb less heat than black animals.