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As a consequence of the increasing spread of microbial resistance to antibiotics and the emergence of new pathogens, the use of orally applied recombinant antibodies such as single-chain Fv proteins (scFvs) for passive immunization is becoming one of the most promising alternatives to combat infectious diseases. scFv has been readily expressed in transgenic bioreactors (animal and plant), which possess great potential for the production of recombinant pharmaceutical proteins. Notwithstanding their reduced size, scFvs are still able to bind antigens with the same affinity as that of the whole antibody, whereas the affinity can be improved and novel functions of scFvs can even be created through the modification of any gene of interest. The recombinant antibody libraries developed from chickens have shown significant diversity over that from other mammalian species such as mice, owing to the mechanism of immunoglobulin gene diversification in birds. Chickens are useful for development of specific antibodies against conserved mammalian proteins because of the phylogenic differences between chickens and mammals. Therefore, recombinant IgY antibodies play an important role as therapeutic and diagnostic research tools in eliminating microbial threats to human and animal health.