Meta-analysis of dietary Bacillus spp. on serum biochemical and antioxidant status and egg quality of laying hens

Abstract

Abstract The purpose of the current meta-analysis was to determine the efficacy of Bacillus spp. (BS) feed additive in enhancing serum biochemical indices (total protein and cholesterol) and antioxidant enzymes (total antioxidant capacity [TAC], catalase [CAT], superoxide dismutase [SOD], glutathione peroxidase [GSH-Px], and malondialdehyde [MDA]) status and egg quality (Haugh unit [HU], eggshell thickness [EST], and eggshell strength [ESS]) of laying chickens. Seventeen articles were identified via a systematic search performed on PubMed, Google Scholar, and Scopus, and results were combined using a variance component model. The results indicate that dietary BS supplementation resulted in higher HU (P < 0.001), EST (P < 0.001), and ESS (P < 0.001) values with evidence of heterogeneity. Furthermore, dietary BS increased total protein (P = 0.008) and GSH-Px (P < 0.001) and reduced the concentrations of CAT (P = 0.018), SOD (P = 0.039) and MDA (P < 0.001) in the serum of laying hens. In contrast, dietary BS did not affect serum cholesterol and TAC in laying chickens. Restricted subgroup analyses showed that the studied moderators (i.e., treatment duration, supplementation level, BS, hen’s age, and hen’s strains) influenced the outcomes of the meta-analysis. Additionally, meta-regression revealed that the studied moderators accounted for most of the sources of variations among the 17 studies utilised for the meta-analysis. In conclusion, dietary BS can be utilised as a nutritional strategy to improve egg quality, serum total proteins, and the serum antioxidant status of laying hens.