Abstract Prebiotic and probiotic products seem to have beneficial effects on the physiological performance of broiler chickens. This study aims to evaluate the effects of dietary supplementation of mannan-oligosaccharide prebiotic (Bio-MOS) and Saccharomyces cerevisiae probiotic (Bio-SAF47), either alone or in combination, on some of the biological markers of heat stress in broiler chickens. 300 one-day-old chicks (Cobb 500) were randomly divided into five groups (n = 12) with 5 repetitions. All groups had access to a basal diet, and experimental groups each additionally received 0.05, 0.1, and 0.2 percent of their respective supplementation regimen in starter, grower, and finisher diets, respectively. Dietary supplementation of Bio-SAF47 and Bio-MOS reduced (p < 0.05) the elevated serum corticosterone concentration during 1-21 and 22- 42 days of age, respectively. Combination of Bio-SAF47 and Bio-MOS reduced (p < 0.05) the elevated serum corticosterone concentration and H/L ratio; while increasing (p < 0.05) the reduced IgG titer, bursa index, BWG, heterophil and lymphocyte count during 35-42 (finisher) days. Our results suggest that prebiotics and probiotics reduce the negative effects of heat stress in broilers and the combination of Bio-SAF47 and Bio-MOS diet (synbiotic effect) was advantageous compared to the control diet with respect to feed efficiency. Moreover, separate supplementation of Bio-SAF47 and Bio-MOS had a positive effect on serum corticosterone levels. These results emphasize the role of prebiotic and probiotic supplementation in improving physiological performance and open a new window to future studies.
