In the chicken, serum gamma globulin (CGG) is preferentially transferred by the follicular epithelium of the ovary to the developing ova. The concentration of gamma globulin in the yolk of the unfertilized egg is many times the concentration of chicken serum albumin (CSA). This transfer occurs largely during the 4 to 5 days preceding ovulation when the growth of the ovum is most rapid. Thus, in the chicken, the follicular epithelium of the ovary serves the same purpose in the passive immunization of offspring as does the acinar epithelium of the udder in ungulates and the extraembryonic membranes in rabbits and man.

The amount of gamma globulin synthesis by the chick is low during the first 2 weeks of life and is associated with low levels of serum gamma globulin. By the end of the 1st month of life, the level of serum gamma globulin increases, presumably reflecting an increased rate of synthesis.

In the adult hens the half-life of I131-labeled CSA is 66 hours and that of I131-labeled CGG, 35 hours, while in the newly hatched chick for I131-labeled CSA it is 42 hours and for I131-labeled CGG, 72 hours. Thus, this species shows a gamma globulin sparing in the first days of life, as do most mammalian species.

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