Du Preez J H
Technology Transfer, Onderstepoort Veterinary Institute, South Africa.
Onderstepoort J Vet Res. 2000 Dec;67(4):263-71.
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.
并非所有参数都适合作为确定奶牛热应激的参数，且并非所有参数都值得信赖。温度湿度指数（THI）仍然是衡量导致奶牛热应激的环境温热程度的最佳、最简单且最实用的指数（参数）。将体温和呼吸频率作为参数来确定奶牛的热应激是切实可行的，易于测定且相对可靠。这些生理参数必须始终与THI值一起用于确定和评估奶牛的热应激。出于实际目的，尽管可以获得急性或慢性热应激的良好指征，但血浆皮质醇浓度和乳成分不能用作确定奶牛热应激的参数。香草酸是牛奶中发现的肾上腺素的分解产物，但在其在牛奶中的浓度可作为奶牛热应激的指标/参数之前，必须更多地了解肾上腺素在牛奶中的药效学。使用最实用的热应激参数，根据奶牛对热应激的适应性进行选择和育种，将确保它们的后代在当前环境条件下具有卓越的性能。
