The immunisation of chickens with Freund's Complete Adjuvant (FCA) significantly reduces the egg-laying frequency in comparison to the use of Freund's Incomplete Adjuvant and Hunter's TiterMax. Although FCA results in higher titers of immunospecific antibody in the egg yolk this is counter-balanced by the reduction in number of eggs produced by the chicken. There is consequently no reason to use FCA in chickens when the egg yolk is used as the antibody source.