The influence of heat stress on energy metabolism in Simmental dairy cows during the periparturient period

Sa？etak Heat stress adversely affects the metabolism and production of dairy cows, particularly during the transition period. The aim of this study was to evaluate energy metabolism in heat stressed dairy cows during the periparturient period. Twenty-four Simmental dairy cows were included in the study. The cows were assigned into two groups according to the season: the summer group (n = 12) and autumn group (n = 12). Physiological parameters (rectal temperature, respiratory and heart rate) and serum metabolic parameters (glucose, triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDL-C), non-esterified fatty acids (NEFA) and beta-hydroxy butyrate (BHB) were measured at days -21, -7, 8, 16, 24, 32 and 40 relative to calving. There were no significant differences in glucose concentration between the investigated groups (P<0.05). Serum NEFA concentration was significantly higher (P<0.05) in the summer group before calving at day -7, while after calving it was significantly lower (P<0.05) at days 16 and 32 of lactation compared to the autumn group. The summer group had lower BHB concentrations after calving compared to the autumn one with statistical significance at days 8, 16 and 24 postpartum (P<0.05). Lipid parameters were also significantly lower (P<0.05) in the summer group after calving, particularly total cholesterol and HDL-C at days 16, 24, 32 and 40 postpartum. The results indicate that changes in energy metabolism in dairy cows under heat stress are directed to reduce NEFA oxidation, in order to limit metabolic heat production. These metabolic adaptations mostly occur after calving because dairy cows are more susceptible to heat stress in early lactation as they produce more metabolic heat during milk production