R. Bras. Zootec.01/May/2011;40(5):1143-7.
Evaporative cooling and cutaneous surface temperature of Holstein cows in tropical conditions
DOI: 10.1590/S1516-35982011000500028
The effects of skin temperature (TS) on the rate of heat loss by cutaneous evaporation (ES) in Holstein cows chronically exposed to sun, considering hair coat colour were studied. Sixteen purebred cows were measured for ES and TS at 01:00 p.m. after 6 hours of exposure to sun, on three body regions (flank, neck and gluteus) and considering dark and white spots separately. Sweating rate (S) and ES were measured by means of a ventilated capsule. Black skin areas presented mean S (138.9 ± 8.5 gm-2 h-1), ES (93.3 ± 5.7 Wm-2), and TS (33.1 ± 0.2°C) higher than those in the white areas (109.5 ± 9.7 gm-2h-1), 73.6 ± 6.5 Wm-2 and 32.6 ± 0.2°C, respectively). There is an exponential relationship among cutaneous temperature and cutaneous evaporation, which can be represented by the equation: ES = 31.5 + exp{(TS – 27.9)/2.19115}, with coefficient of determination r2 = 0.68. Cutaneous evaporative heat loss remains almost constant around 48 Wm-2 until TS reaches nearly 31°C.
Keywords: cutaneous evaporation; cutaneous temperature; Holstein cows