Adipose tissue activity regulates metabolic responses to heat stress in periparturient dairy cows

The thermal environment is an important factor that can influence cow’s performance and production. Heat stress during the hot season might affect energy metabolism, particularly lipid metabolism and antioxidant status as well as the adipose tissue activity. Adipose tissue is the major source of energy in transition dairy cows and plays a key role in the integration of energy metabolism by producing metabolic hormones, leptin (LP) and adiponectin (ADP), which modulate energy homeostasis. The aim of this study was to investigate the effects of heat stress during summer on adipose tissue activity, lipid metabolism and antioxidant activity. The study was conducted on 24 Simmental dairy cows assigned into two groups according to season: summer (S group, N=12) and autumn (A group, N=12). Blood samples were taken on days -21, -7, 8, 16, 24, 32 and 40 relative to parturition. Serum nonesterified fatty acids (NEFA), β-hydroxybutirate (BHB) and HDL-cholesterol (HDL-C) concentrations were assayed spectrometrically by the standard commercial kits. Serum LP and ADP concentrations were assayed by the quantitative ELISA methods. The paraoxonase-1 (PON1) activity was measured spectrometrically by the method of hydrolysis of paraoxon. The average temperature-humidity index (THI) was calculated and was statistically higher in the S group (78.9) than in the A group (58.6) indicating moderate heat stress in the S group. Serum LP concentration was significantly lower in summer (1.23 ng/ml) than in autumn (1.80 ng/ml), while ADP concentration was significantly higher in summer (9.39 ng/ml) than in autumn (2.88 ng/ml). Additionally, significant inversed correlations have been found between LP and ADP in both the S group (r= -0.55 ; P<0.0001) and the A group (r= -0.69 ; P<0.0001). There were no significant differences in NEFA and HDL-C concentrations, PON1 activity and the ratio PON1/HDL-C between the groups while BHB concentration was significantly higher in the A group compared to the S group. These results indicate that adipokines by their actions, both LP and ADP, might regulate negative effects of heat stress on energy balance, lipomobilisation and antioxidant activity and thus could counteract an adverse repercussion on cow’s production and fertility.