Abstract
In recent years, the use of Saccharomyces cerevisiae (SC) as a probiotic, its cell-wall derived mannan-oligosaccharides (MOS) as a prebiotic, and their combined application as a synbiotic has gained recognition as an effective nutritional strategy to replace the non- therapeutic use of antibiotics in animal feed. The present study investigated the effects of dietary supplementation with SC, MOS, and their combination (SC+MOS) on growth performance, intestinal morphology, hematological indices, immune responses, and economic efficiency in Ross-308 broiler chickens. A total of 200 day-old chicks were randomly assigned to four dietary treatments in a completely randomized design, with five replicates of ten birds each. The dietary treatments included a basal diet (T₁, control), SC at 1 g/kg feed (T₂), MOS at 1 g/kg feed (T₃), and a synbiotic combination of SC and MOS at 0.5 g/kg each (T₄). Birds receiving the synbiotic diet exhibited significantly greater cumulative feed intake and body weight gain, along with the most efficient feed conversion ratio, compared to the control and other supplemented groups (P < 0.001). Intestinal morphology was markedly improved in synbiotic-fed birds (P < 0.001), as evidenced by increased villus height, reduced crypt depth, and a higher villus height-to-crypt depth ratio. Hematological parameters, including red blood cell count, hemoglobin concentration, and packed cell volume, were significantly elevated in the probiotic group (P < 0.001), whereas white blood cell counts were highest in the prebiotic group. Both humoral and innate immune responses were enhanced, as indicated by higher Newcastle disease antibody titers in the synbiotic and probiotic groups (P < 0.01) and increased phagocytic activity in synbiotic-fed birds (P < 0.001). Economically, synbiotic supplementation resulted in the greatest profitability, followed by prebiotic, probiotic, and control diets. Taken together, these findings demonstrate that synbiotic supplementation confers superior improvements in growth performance, intestinal health, immune competence, and economic returns, supporting its use as a sustainable and effective feed additive in modern broiler production systems.