The Impact of in Ovo Administration of Probiotic Lactobacilli on the Gut Health and Immune Competence of Broiler Chickens

Due to the incomplete development of their immune system, newly hatched chicks are vulnerable to a wide range of pathogenic microorganisms, including enteric bacterial pathogens during the early stage of life. To boost their immune system during this critical period, numerous studies suggest early feeding, either in ovo or immediately post-hatch, of nutrients and immunomodulators such as prebiotics, probiotics, phytobiotics, Toll-like receptors (TLRs) ligands, vitamins and minerals. Probiotics, defined as live, non-pathogenic microorganisms that confer beneficial effects on the host, have been extensively studied for their effects on poultry health. Supplementation of probiotics to chickens has demonstrated a broad spectrum of advantages, including the modulation of gut mucosal immunity and microbiome composition, enhancement of antibody production, mucus secretion, maintenance of intestinal gut barrier function, and competitive exclusion of harmful pathogens. The effects of probiotics supplementation on chicken gut health, particularly gut immune system and microbiome composition, have been extensively investigated. However, little is known about their effects on the gut health of chick embryos and newly hatched chicks. The primary aim of these studies was to determine whether in ovo probiotic administration alters the expression of key immune genes in the intestine and bursa of Fabricius, as a major lymphoid organ within the gut-associated lymphoid organs (GALT) in chick embryos, and to evaluate its impact on gut microbiome composition and immune responses in newly hatched chicks.