Heat exchange mechanisms of native wool less sheep in a tropical environment

The present study aimed to evaluate the heat exchange mechanisms in red and white varieties of Morada Nova sheep, in order to determine which variety is more adapted to the Semiarid environment. There were measured 121 animals (80 red and 41 white ewes) from three herds located in an equatorial semiarid region. Cutaneous evaporation (CE; Wm^-2), surface temperature (ST, ?C), rectal temperature (RT, ?C), respiratory rate (RR, breaths/min) and convective losses were measured. Samplings were made once at a month from April to October, and the data were recorded from 11h00min to 14h00min. The animals were exposed directly to the sun thirty minutes before being evaluated. Environmental variables registered were air temperature (AT, ?C), black globe temperature (GT, ?C), partial air vapour pressure (PV, kPa) and wind speed (W, ms^-1). There were observed air temperatures higher than 30?C in every month during the experimental period. Average of air temperature was 34.3?C in October, close to the higher critical temperature for sheep. Body region did not affect CE but was a significant effect upon ST; the flank was warmer (40.9 ?C) than neck (38.6?C). Animal variety was a significant effect on both ST and CE; the red variety showed higher ST (40.9?C) but lower CE (219.5 W.m^-2), while white ewes showed lower ST (37.2?C) and higher CE (274.5 W.m^-2). RT, RR and convective losses were higher in the red (39.4?C, 92 breaths/min and 31 W.m^-2, respectively) than in the white variety (39.2?C, 65 breaths/min and 27.5 W.m^-2, respectively). These results showed that both varieties could sustain thermal equilibrium in the semiarid environment. However, the findings suggest also that the two varieties activated the thermoregulatory mechanisms differently, so that red animals used respiratory thermal exchange more intensively, while white animals used more cutaneous evaporation.