Abstract:
The study examined skin temperature (ST) and sweating rate (SR) responses on the black and white skin areas associated with rectal temperature (RT) and respiratory rate (RR) of 2 Friesian bull calves, aged 5 months and weighing 115 kg. The animals were assigned to 2 climatic environments; one group was tested under indoor housing, the second one was under indoor-outdoor-indoor conditions. In each test period half hourly physiological measurements were taken from 1100h to 1600h indoors, whereas the second group was tested indoors from 1100h to1200h and then exposed to the sun without any shade for an outdoor physiological responses from 1230h to 1430h, then moved indoors till 1600h. The calves in this experiment were subjected to either hot dry or hot humid environments and were long-wooly coated animals with 60% of black skin. Mean RT and RR under outdoor conditions were highly significant higher (P<0.01) than those under indoor housing (39.8 v. 39.1�C; 134.7 v. 74.2 breaths/min, respectively). Mean ST and SR under outdoor conditions on both black and white skin areas were also highly significant greater than their indoor counterparts (36.7 v. 33.9�C; 77.6 v. 35.6 g/m2/h, respectively). Under both indoor and outdoor conditions, ST and SR on the black skin areas appeared to be more sensitive to environmental changes than those in the white one. This study shows that cutaneous evaporation is closely controlled by ST and that the proportion of black skin area has an important role in both heat absorption and heat dissipation which affect thermoregulation and, indirectly, production. Future studies should investigate differences in sweat gland density and the innervation of the black skin areas.
