Relationship between the concentration of metabolites (glucose, NEFA, BHB and urea) and milk production in cows under heat stress | Ispitivanje korelacije između koncentracije metabilita (glukoza, NEFA, BHB i urea) i prizvodnje mleka kod krava u toplotnom stresu

Cattle production is due to climate change are increasingly burdened by extreme weather conditions and heat stress. The negative effect of heat stress on milk production and reproductive activity of cows developed a research about the metabolic adaptation of cows in heat stress. The aim of this study was to evaluate the correlation between milk production and concentrations of glucose, nonesterified fatty acids (NEFA), beta-hydroxybutyrate (BHB) and urea in dairy cows during heat stress. Milk production is positively correlated with the concentration of glucose in v.jugularis, and negatively with the concentration of urea in the same vein. Correlation with NEFA and BHB in the same vein is a negative, but not statistically significant. The correlation between milk production and concentrations of glucose and urea v.subcut.abdominis is negative. The value of NEFA and BHB in the same vein, do not show a significant correlation with milk production. A significant correlation was found between milk yield and the difference between the values of glucose, NEFA and BHB measured in two veins. Greater the difference in glucose concentration between the two veins means greater milk production (positive correlation), and the greater the difference in concentration of NEFA and BHB between two veins negatively correlated with milk production. Since the concentration of metabolites in v.subcut.abdomnis depends on the use of these metabolites in the mammary gland, we can conclude that the difference in concentration between the metabolites in v.jugularis and v.subcut.abdominis arises from the use of metabolites in the mammary gland. This leads to the further conclusion that the greater use of glucose in the mammary gland during heat stress leads to increased milk production, and increased use of fatty metabolites decreased milk production, while higher concentrations of urea has a negative impact on milk production. Reduced blood glucose concentration, elevated concentrations of urea and increased utilization of NEFA and BHB in the udder may be associated with reduced milk production in cows during heat stress.