Individual and Combined Effect of Zinc-L-Selenomethionine Complex with Mannan-Oligosaccharide on Growth Performance, Carcass Characteristics, Gut Development and Immune Response in Broilers

Due to the increased restrictions on antibiotic growth promoters (AGPs), natural substitutes such as organic selenium and prebiotics are gaining increased attention to enhance the gut health and performance of broilers. This study aimed at assessing the effects of organic selenium separately and in combination with mannan-oligosaccharides (MOSs) on gut development, immunity, carcass traits and overall growth performance in broiler chickens. For this study, 528-day-old straight-run broiler chicks (Ross-308) were assigned to four dietary treatments (six replicates of 22 birds each), in a completely randomized design under a 2 × 2 factorial layout, including: (1) Se0.2 (0.20 mg/kg organic selenium), (2) Se0.2 + MOS (0.20 mg/kg selenium + 1 g/kg MOS), (3) Se0.4 (0.40 mg/kg selenium) and (4) Se0.4 + MOS (0.40 mg/kg selenium + 1 g/kg MOS). The results showed that the lower level of organic selenium, along with MOS (Se0.2 + MOS), resulted in significantly enhanced (<i>p</i> ≤ 0.05) feed conversion ratio, body weight gain and livability. Whereas the higher level of organic selenium, along with prebiotic (Se0.4 + MOS), remarkably (<i>p</i> ≤ 0.05) improved carcass traits, immunity and villus height in broilers. In conclusion, the combined provision of 0.4 mg/kg organic Se and 1 g/kg MOS optimally enhances broiler performance, immunity and gut health, offering a promising substitute to AGPs.