A large amount of antibiotics has long been used to control pathogenic diseases and as growth promoters to improve performance in livestock. However, this approach had significant and unwanted side-effects, such as development of antimicrobial resistance and carry-over of the antibiotic residues to poultry products. In this light, the use of antibiotics as growth promoters (AGPs) was banned by the European Union since 2006, based on their possible negative consequences for animal health and food safety. This ban has led to animal performance problems and the increased incidence of enteric diseases in farms, with serious economic damage. In the post-antibiotics era, probiotics, prebiotics and synbiotics are proposed as alternatives to AGPs in poultry production. To be effective, these compounds have to be administered to the animals under fully controlled conditions and as early as possible. In ovo technology enables delivery of sustainable bioactives, such as pre-/probiotics and their combination, directly into the egg air chamber at day 12 of embryonic incubation. Previously, different types of prebiotics and the routes of delivery, as well as their synergistic combinations with probiotics, were tested in field and laboratory trials also by our research groups. Some of the obtained results (in vivo performance, slaughter and meat quality traits) are described hereinafter.