The concentration of antibody in the egg yolk is somewhat higher than that found in serum. Whereas human serum typically contains IgG at 10-12 mg/ml, egg yolk contains IgY at 15-25 mg/ml (Akita and Nakai, 1993). Presumably, this high concentration is important for conferring passive immunity to newly hatched chicks.
The rate of antibody production in laying chickens is remarkable. According to Larsson et al. (1993), "in one week, a hen produces egg antibodies equivalent to 90-100 ml of serum." This article also states that "only large mammals, such as cows or horses, can produce more antibodies than a laying hen." Gassmann et al. (1990) states that "the amount of purified IgY produced in one month is 18 times higher than that of IgG produced in a rabbit."