The almost extreme properties of antibodies to recognize small specific structures on other molecules have made them an indispensable tool in laboratory in various applications such as research, diagnostic and therapy. Antibodies presently available for these purposes are mostly mammalian monoclonal or polyclonal antibodies. The production of these antibodies requires normally the use of laboratory animals. Nowadays, most classical chosen mammals for polyclonal and monoclonal antibodies are rabbits and mice, respectively. The procedure involves two steps, each of which causes distress to the animals: the immunization itself and repeated bleeding or scarifying for spleen removal, which is a prerequisite for antibodies preparation.
In 1893, Klemperer first demonstrated that the immunization of a hen resulted in the transfer of specific antibodies from the serum to the egg yolk. For over a hundred years there was no scientific application for this knowledge. But when the animal welfare became a matter of serious ethical concern for the scientific community, the results of Klemperer have attracted a great attention, particularly since the 1980s.
In the sense of animal welfare, the use of laying hens for antibody production represents a refinement and a reduction in animal use. It is a refinement in that the painful and invasive blood sampling or scarifying are replaced by collecting eggs. It entails a reduction in the number of animals used because the antibodies productivity in laying hens is nearly 20 times greater than that in rabbits (Schade et al., 2004).
With the ban on sub-therapeutic antibiotic usage in Europe and the increasingly strictness of the European legislation on food hygiene, passive immunization by oral administration of pathogen-specific hen egg yolk antibody (IgY) may be a useful and attractive alternative. Furthermore, because of the high yolk antibodies concentration, over 100 mg of antibodies can be obtained from one egg (Akita et al., 1992). Since a laying hen produces approximately 25 eggs per month, 5 g of antibody per month may be obtained from a single laying hen.