1. The references for the bibliography used in the systematic review included in level 3 of DistillerSR (1144 articles) are available in appendix A
2. Toll‐like receptors: critical proteins linking innate and acquired immunity;Akira;Nat Immunol,2001
3. Regulation of genetically modified organisms (GMOs) in the European Union: principles of risk assessment;Anadón;Veterinary and human toxicology,2004
4. Probiotics for animal nutrition in the European Union. Regulation and safety assessment;Anadón;Regulatory Toxicology and Pharmacology,2006
5. Establishment of immune competence in the avian GALT during the immediate post‐hatch period;Bar‐Shira;Dev Comp Immunol,2003