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Effect of heat stress on metabolic and antioxidant responses in periparturient dairy cows

Global warming greatly affects performance and production of dairy cows having a significant impact on dairy industry. Exposure to heat stress decreases feed intake of cows compromising energy metabolism and immune system which might reduce disease resistance and production potential. The objective of this study was to evaluate metabolic and antioxidant responses to heat stress during summer in periparturient dairy cows. The study was conducted on 24 Simmental dairy cows kept in a barn with favourable air flow condition. The cows were 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 macro mineral (Ca, K, Na, Cl) concentrations were assayed spectrometrically by commercial kits (Randox, UK). Serum superoxide-dismutase (SOD) activity was assayed by the quantitative ELISA method while paraoxonase-1 (PON1) activity was measured spectrometrically by the method of hydrolysis of paraoxon. The heart and respiratory rates and rectal temperature were monitored at each sampling time. The average temperature-humidity index (THI) was statistically higher in summer (78.9) than in autumn (58.6) indicating moderate heat stress in the S group. Rectal temperature and the respiratory rate were significantly higher in the S group (39.1°C and 50, respectively) than in the A group (38.7°C and 27, respectively) while the heart rate was not affected. Serum SOD was significantly lower in summer (24 U/ml) than in autumn (39 U/ml) while PON1 activity was only slightly lower in summer. Serum NEFA was not affected while BHB was significantly lower in summer. Electrolyte balance was altered as well. The results indicated that dairy cows responded to heat stress by complex metabolic adaptation affecting metabolic homeostasis and antioxidant protection aiming to counteract detrimental effects of reduced nutrient and energy intake.

heat stress, lipid mobilisation, antioxidants, macrominerals, dairy cows

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