Immunoglobulin IgG1 metabolism in new born calves.

The half-life of IgG1 immunoglobulin was measured in six neonatal calves following a meal of iodine-125 labeled IgG1 in colostrum derived from their dams. The half-life as measured by the decrease in plasma concentration of IgG1 was 19.9 +/- 1.9 days. However, the half-life as measured by the disappearance of [iodine-125]IgG1 from the plasma was 11.5 +/- .6 days. The latter value is closer to the true half-life because it is not affected by endogenous production of IgG1 by the tissues of the young calf. A decrease in the specific activity of plasma [iodine-125]IgG1 with time representing the body "pool" of IgG1 (half-life 25.8 +/- 6.1 days) suggests that the calf from birth to about 20 days of age is capable of synthesizing a significant amount of IgG1 immunoglobulin.