Heat stress of dairy cows in Serbia: Review

The climatic conditions in Serbia are suitable for the development of heat stress in cows. The values of the bioclimatic THI indicator point to a positive trend in increase in the number of days during which the conditions for the occurrence of heat stress are present. In cows, a change in body temperature is noted, activation of the cooling mechanisms, along with reduced milk production and reproductive efficiency. The behavioral changes of cows occur on farms, and the level of welfare decreases slightly when measured according to animal-based criteria. Changes in productivity are mainly related to metabolic, hematological and inflammatory adaptations. The metabolic adaptation that leads to a decrease in milk production is related to an increase in sensitivity to insulin with reduced lipolysis, an increase in TNF-a in cows, as well as to metabolic rearrangements of the mammary gland. Reproductive efficiency is reduced and is characterized by reduced expression of estrus and reduced response to estrus induction procedures. High ambient temperatures, in in vitro conditions, can affect the stability of laboratory parameters in the blood serum of cows. Cows exhibit different profiles of resilience to heat stress, and the study of resilience curves, for productive and blood parameters, represents the starting point for selecting cows that will tolerate heat stress better. For this purpose, the cumulative effects of heat stress expressed in the area under the resilience curve can be used. Certain precautionary measures such as providing shade, cooling by using fans and sprinklers or some other advanced technological methods, can reduce losses during heat stress. All of the above indicate that it is necessary to pay extra attention to all aspects of health care and production on cow farms in Serbia during late spring and summer when the animals are exposed to heat stress.