Effect of heat stress on the values of biochemical blood parameters of dairy cattle

The aim of the study was to determine the effect of heat stress on differences between selected biochemical blood parameters in cows in June and October, taking into account different housing systems and cooling systems used. The research was carried out on 60 cows from stanchion barns (farm A) and loose-house barns (farm B). Material for research, venous blood, was collected at the same time, in the morning, after milking and clinical examination. Then, parameters describing the energy balance and the activity indexes of the parenchymal organs as well as the mineral balance were determined. Milk production in both farms was clearly lower in June than in October, but the difference between milk yields obtained from the two farms was over 15% in June and only less than 10% (5-6 kg of milk) in October. Both farms A and B showed an increase in aspartate aminotransferase and creatine kinase. In farm A, the statistically significant increase exceeded the normal physiological range, which could indicate developing disturbances in the locomotor system caused by the impact of high temperature. Energy balance disturbances occurred only in farm A, where a statistically significant decrease in glucose and cholesterol concentration was found in June samples, which, according to the authors, could be related to a higher energy demand. The results of biochemical tests of venous blood collected in June may indicate the onset of fatty liver in cows (decreased cholesterol, glucose, and total protein levels, as well as increased bilirubin levels and GGTP activity) as a consequence of exposure to high temperatures. Heat stress has a significant impact on the functioning of the cow's organism, which will not always be manifested by characteristic clinical signs. Accurate laboratory analyses make it possible to diagnose changes developing as a result of cows being exposed to heat stress.