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The effect of two kinds of probiotics different in their mode of actions was tested on rabbits’ performance grew under hot summer conditions. Fiftysix New Zealand White rabbits (5-weeks-old) were fed on growing diet and orally supplemented with Saccharomyces cerevisiae (S. cerevisiae) 0.5, 1 and 1.5 g., Lactobacillus acidophilus (L. acidophilus) 1, 2 and 3×109 CFU/kg body weight or distilled water as a control. Calculated temperature humidity index was classified as severe heat stress. Significant improvements in productive parameters, (average daily gain and feed conversion ratio) were detected in the high-dose group (3×109 CFU/kg) of L. acidophilus. Similarly, the haemoglobin concentration, red blood cell count and fT3 serum levels were considerably higher in the L. acidophilus groups, with significantly lower cortisol levels. The mean duration of anxiety-related behavioural responses in the open field test showed significant improvements in treated groups. Also, microbiological investigation showed an absence of some pathogenic bacterial species (Salmonella spp, Clostridium spp and Enterobacteria spp) in treated groups and the presence of beneficial yeast species (Yarrowia lipolytica) in the L. acidophilus-supplemented groups. Conclusively, administration of S. cerevisiae and L. acidophilus for consecutive 8 weeks may counteract the consequences of chronic heat stress in growing rabbits. [ABSTRACT FROM AUTHOR]