Abstract

Information on effects of weather conditions on milk production of dairy cows is rather scarce. Legislation exists in some countries saying when and how protection should be available for cows on pasture. Producers refer to the extra costs, and are not always convinced of the return of investment. Therefore, (re)production variables of high producing dairy cows were reviewed in relation to weather conditions in a mild climate. The objective was to understand mechanisms cows are using for acclimatization, which might affect (re)production, and to propose managing tools. An overall critical dry air temperature seems to be about 16 °C, with cumulative interactions from relative humidity, wind speed, radiation and rain fall. The explanation is related to the cow’s thermoregulatory physiology associated with her heat and energy balance, as a primary need. Modulating factors, such as breed, individual capacity, feed composition and farm management have to be taken into account.

The effects have to be considered as important at herd level, especially in a system with year round calving, since production might be below peak production up to six months of the year. Planning of day of calving should avoid peak production during summer, since mild heat stress might counteract the expression of genetic progress for (re)production. However, since the most important factor seems to be the level of dry air temperature, the effects will be independent of protection or not. Hence, there will be no direct return of investment moneywise, but indirectly as appreciation from society for animal welfare.

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