Abstract
The primary objective of this study was to evaluate the effects of liquid (F-LAB) and commercial (C-LAB) probiotics sourced from Rye-Grass Lactic Acid Bacteria on broiler chickens experiencing heat stress (HS). The research involved 240 broiler chicks divided into six groups: control, F-LAB, C-LAB (raised at 24°C), HS, F-LAB/HS, and C-LAB/HS (exposed to 5–7 hours of 34–36°C daily). While F-LAB and HS/F-LAB groups received a natural probiotic added to their drinking water at a rate of 0.5 ml/L, C-LAB and HS/C-LAB groups were supplemented with a commercial probiotic at the same dosage. No probiotic supplementation was administered to the control and HS groups. The results revealed that without probiotic supplementation, heat stress led to a decrease in body weight gain, T3 levels, citrulline, and growth hormone levels, along with an increase in the feed conversion ratio, serum corticosterone, HSP70, ALT, AST, and leptin levels. Heat stress also adversely affected cecal microbiota, reducing lactic acid bacteria (LABC) while increasing Escherichia coli and coliform bacteria (CBC) counts. However, in the groups receiving probiotic supplementation under heat stress (F-LAB/HS and C-LAB/HS), these effects were alleviated. Particularly noteworthy was the observation that broiler chickens supplemented with natural lactic acid bacteria (F-LAB) exhibited greater resilience to heat stress compared to those receiving the commercial probiotic, as evidenced by improvements in growth, liver function, hormonal balance, intestinal health, and cecal microbiome ecology. These findings suggest that the supplementation of naturally sourced probiotics (F-LAB) may positively impact the intestinal health of broiler chickens exposed to heat stress, potentially supporting growth and health parameters.