Abstract
Background:
Recently, alternative antibiotic growth promoters, such as probiotics and postbiotics, have gained interest in combating antibiotic-resistant bacteria in the food chain.

Aim:
This study aimed to assess the effects of probiotics and postbiotics on broiler performance, immune response, and cecal microbial composition.

Methods:
A total of 225 one-day-old male Cobb 500 broiler chicks were randomly allocated into three experimental groups (75 birds / group) and subdivided into three replicates of 25 birds each. Group 1 was a control group that received a basic diet. Group 2 was probiotic-treated and offered a basal diet enriched with 100 g/ton of live yeast (Saccharomyces cerevisiae var. boulardii). Group 3 was postbiotic-treated and provided with a basal diet blended with 350 g/ton of Diamond V XP postbiotic product. Weekly measurements comprised body weight (BW), feed consumption (FC), and feed conversion ratio (FCR) throughout the 35-day trial. Serum IgM and IgY levels were estimated on days 21 and 35 of the study. Microbial balance in the cecum was assessed.

Results:
From day 1 to day 21 of the trial, the probiotic and postbiotic groups showed a considerable enhancement in BW development compared with the control group; nevertheless, from day 21 until the end of the investigation, the postbiotic group showed superior BW development compared with both the probiotic and control groups (2213.7 ± 21.6 vs 2152.5 ± 15.3 and 2026.9 ± 9.9). Cumulative BWG data also highlighted that the postbiotic group achieved a remarkable rise, in contrast with the control group. The probiotic and postbiotic groups exhibited substantially improved FCR throughout the trial compared with the control group, with no discernible variation in FC. At 21 days, the probiotic and postbiotic groups had notably higher IgM levels than the control group (3.9 ± 0.4 and 3.9 ± 0.3 vs. 2.9 ± 0.2, respectively). Furthermore, the probiotic and postbiotic groups recorded substantially reduced pathogenic E. coli counts and significantly higher Lactobacillus spp counts compared with the control group.

Conclusion:
Broiler diets enriched with Saccharomyces cerevisiae and its postbiotic enhance immunity, gut health, and broiler performance. Notably, the postbiotic showed better BW development than the probiotic, especially at the last stages of the broiler productive period, which warrants further investigation.

Key words: Broiler; Growth performance; Gut health; Immunity; Postbiotic.