Aim: The current study aimed to compare the impact of heat stress (HS) on some physiological functions and blood oxidative stress biomarkers between dry dairy crossbred (Balady X Friesian) cows and buffaloes during Egyptian summer season (July-September).

Materials and Methods: A total of 26 healthy animals were equally used in the in the current study. The criterion for cows and buffaloes selection and the management conditions were similar. A total mixed ration to meet the animal's requirements was used, and dry matter intake (DMI) was calculated. Ambient temperature, relative humidity, temperature humidity index (THI), respiratory rate, and rectal temperature (RT) were daily recorded. Meanwhile, live body weight and body condition score were weekly recorded. Blood samples were collected bi-weekly, and plasma samples were harvested for malondialdehyde (MDA) content and enzymatic antioxidants such as glutathione peroxidase, superoxide dismutase, and catalase activities determinations throughout the experimental period (8 weeks - prepartum).

Results: The results confirmed, the HS condition, as the THI values ranged from 79.74 to 90.4 throughout the experimental period. In both species, HS increased RT and decreased DMI (<10.5 kg/day and 9.5 kg/day in cows and buffaloes, respectively). Buffaloes seemed to be more affected by the hostile environmental condition of this study compared with their respective cows. Buffaloes had recorded up to 1 °C increase in their RTs in most of the point's period compared to cows. There was a continuous increase in MDA values (194.7 and 208.4 nmol/gHb in buffaloes and cows, respectively, 2 weeks prepartum) as the animals come close to parturition with moderate decrements for the enzymatic antioxidant activities in both cows and buffaloes.

Conclusion: It can be concluded that during Egyptian's summer season, HS had adversely affected feed intake and consequently animal's production performances.

Keywords: buffaloes, dairy cows, Egyptian's summer, heat stress, oxidative stress.

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