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

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.

Bibliographic Details

Main Authors:	Silva,Roberto Gomes da, Maia,Alex Sandro Campos
Format:	Digital revista
Language:	English
Published:	Sociedade Brasileira de Zootecnia 2011
Online Access:	http://old.scielo.br/scielo.php?script=sci_arttext&pid=S1516-35982011000500028
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