engleski

Influence of seasonal heat stress on reproductive performance in dairy cows

Seasonal heat stress is one of the major factor contributing to decreased fertility and poor reproductive performance in dairy cows. High environmental temperature might directly influence fertility by impairing cellular function of reproductive cells. Additionally, heat stress can affect reproduction by decreased appetite and reduced nutrient intake with a consequence of lower energy balance. The aim of this study was to investigate the influence of seasonal heat stress on reproductive capability in dairy heifers. The study was conducted on thirty-two healthy Holstein-Frisian dairy heifers kept in an open free-stall barn assigned into two groups according to season: winter (N=14) and summer (N=18). Reproduction parameters were recorded from the time of first insemination of heifers until successful insemination after the first calving. Additionally, blood samples were taken at the time of insemination and during the transition for antioxidant and metabolic status measurement. The calving-to-conception (CC) interval was prolonged in the summer group (159  76.4 days) as compared to the winter one (91  46.7 days). A conception rate (CR) was significantly lower (P<0.05) in summer than in winter after the first calving, whereas no difference was observed in the CR in heifers at the first service between summer and winter. The concentrations of NEFA and BHB were significantly higher (P<0.05) during the transition in summer than in winter. Antioxidant status measured by the total antioxidant status (TAS) and paraoxonase-1 (PON1) activity was significantly decreased (P<0.05) in summer as compared to winter during the transition period. The results demonstrated that heat-stressed cows inseminated during hot months had lower fertility rate coupled by a higher degree of NEB and lower antioxidant status.

heat stress, dairy cows, lipid mobilisation, reproduction

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