Evaporative cooling and cutaneous surface temperature of Holstein cows in tropical conditions

Roberto Gomes Da Silva,Alex Sandro Campos Maia

doi:10.1590/s1516-35982011000500028

Abstract

The effects of skin temperature (T S) on the rate of heat loss by cutaneous evaporation (E S) in Holstein cows chronically exposed to sun, considering hair coat colour were studied. Sixteen purebred cows were measured for E S and T S 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 E S were measured by means of a ventilated capsule. Black skin areas presented mean S (138.9 ± 8.5 gm-2 h-1), E S (93.3 ± 5.7 Wm-2), and T S (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: E S = 31.5 + exp{(T S - 27.9)/2.19115}, with coefficient of determination r² = 0.68. Cutaneous evaporative heat loss remains almost constant around 48 Wm-2 until T S reaches nearly 31°C.

Highlights

Heat losses by convection and by long-wave radiation depend on the temperature difference between the surface of the animal and its environment
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
The objective of this study was to investigate the relationship of the skin temperature on the cutaneous evaporation rate of Holstein cattle bred in a tropical region

Summary

Introduction

Heat losses by convection and by long-wave radiation depend on the temperature difference between the surface of the animal and its environment. Thermal comfort of an animal in those regions depends largely on its ability to dissipate excess of body heat by evaporative cooling either from cutaneous and respiratory surfaces (McLean, 1963b; Gatenby, 1980; Gebremedhin et al, 1981; Gebremedhin & Wu, 2001, 2002; Maia et al, 2005). Direct determination of the evaporation from the skin surface by means of ventilated capsules has been used (McLean, 1963a.; Gatenby, 1980; Maia et al, 2005)

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