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The results obtained in a two-year experimental trial carried out on Italian Friesian cows and in different Italian areas, have been used to define a thermal comfort index. It allows an assessment of the changes of milk production and breathing rate of the dairy cows inside the cowshed estimated from the microclimatic conditions (temperature, relative humidity and air speed) of the dairy cows.

This can be extremely useful for herd management because the dairyman, according to the productive features of its dairy cows and on the weather conditions of the geographical area, can consider in advance the economic benefits of installing an air conditioning system to mitigate the heat stress for the cows.

It is obvious benefits increase by increasing the productive performances of the cows, and it is of major importance in hot areas where the heat stress for the animals is higher and more prolonged. In extreme thermal conditions, the modification in the cows endocrine-metabolic behaviour are so marked that they can not quickly return to normal state once the stress conditions end.