Abstract:
Not all parameters are trustworthy and practical to use as parameters to determine heat stress in dairy
cattle. The temperature-humidity index (THI) is still the best, simplest and most practical index (parameter)
for measurement of environmental warmth which cause heat stress in dairy cattle. It is practical,
easy to determine and relatively trustworthy to use body temperature and respiratory rate as
parameters to determine heat stress in dairy cattle. These physiological parameters must always be
used together with THI values to determine and evaluate heat stress in dairy cattle.
For practical purposes, plasma cortisol concentration and milk composition cannot be used as parameters
to determine heat stress in dairy cattle although good indications of acute or chronic heat
stress can be obtained. Vanillic acid is a break-down product of adrenalin found in milk, but before its
concentration in milk can be used as an indicator/parameter of heat stress in dairy cows, more about
the pharmacodynamics of adrenaline in the milk has to be known. Selection and breeding of dairy
cows on the basis of their adaptibility to heat stress using the most practical heat stress parameters
will ensure that their offspring will have superior performance in the prevailing environmental conditions.
