Endogenous Production of Immunoglobulin lgG1 in Newborn Calves

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Abstract
There is a decrease in the specific activity of labeled Ig[immunoglobulin]G1 in serum over 3 wk following the feeding of 125I-labeled IgG1 in colostrum to calves at birth. This decrease indicated the appearance of new IgG1 from some source. To determine if this new IgG1 came from endogenous production in the calf or from continued small amount of intestinal absorption from milk, labeled IgG1 was added to normal milk and fed to calves of various ages up to 3 wk after an initial feeding of colostrum at birth. Labeled IgG1 was added to colostrum fed to calves at birth, and the calves were maintained on a normal milk diet or fed a synthetic milk diet. Determination of 125I in the serum protein fractions of these calves indicated that there was no apparent intestinal absorption of labeled IgG1 from the milk in the period from 2 days to 3 wk. Comparable decreases occurred in the specific activity of labeled IgG1 in serum in the calves fed the labeled IgG1 in colostrum at birth and subsequently maintained either on a diet including milk or on the synthetic milk diet devoid of IgG1. The origin of new IgG1 in the calf after .apprxeq. 36 h and up to .apprxeq. 3 wk of age apparently arises from endogenous production at a rate of .apprxeq. 1 g IgG1/day.