Effects of a multi-strain probiotic on production performance, antioxidant indices, intestinal morphology, and fecal microbiota in heat-stressed quails.

This experiment aimed to assess the impact of a multi-strain probiotic cocktail containing spore-forming and lactic acid-producing species on the growth performance, intestinal morphometry, antioxidant indices, and fecal bacterial populations of Japanese quails reared under heat stress (HS) conditions. A total of 400 one-day-old unsexed Japanese quails were randomly allocated to four experimental groups (100 birds per group; four replicates of 25 birds each): (1) Control (normal temperature), (2) Probiotic (normal temperature + probiotic), (3) Heat stress (HS), and (4) HS + Probiotic. The probiotic cocktail, containing six bacterial strains, was administered via drinking water at a concentration of 1 g/L (equivalent to 6 × 10⁹ CFU/g) from day 1 to day 42. Heat stress was applied from day 21 to day 42 by exposing birds to 38 ± 2 °C for 8 h daily, while the control groups were maintained at 24 ± 2 °C. The HS+Probiotic group exhibited significantly lower final body weight compared to the other groups (P < 0.05), and the lowest feed intake and highest feed conversion ratio (FCR) were observed in the HS and HS+Probiotic groups, respectively. The HS and HS+probiotic groups had significantly lower serum total antioxidant capacity (TAC) levels compared to the probiotic group (P < 0.05). The highest length of villus in both the jejunum and ileum was observed in the probiotic-treated groups (P < 0.05). In contrast, the villus length-to-crypt depth (VL/CD) ratio in the jejunum was significantly lower in the HS group than in the other experimental groups (P < 0.05). Fecal total bacteria and fecal Enterobacteriaceae counts were notably lower in the probiotic group (P < 0.05). The HS group showed a notably lower spore-forming bacterial count than the control (P < 0.05). It is concluded that adding probiotics to the drinking water of heat-stressed quails improved intestinal morphometry but did not significantly enhance production performance.