Endogenous Production of Immunoglobulin lgG1 in Newborn Calves

Abstract

There is a decrease in the specific activity of labeled IgGl of serum over 3 wk following the feeding of iodine-125 labeled immunoglobulin IgGl in colostrum to calves at birth. This decrease indicated the appearance of new IgGl from some source. To determine if this new IgGl came from endogenous production in the calf or from continued small amount of intestinal absorption from milk, labeled IgGl 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 IgGl was also 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 iodine-125 in the serum protein fractions of these calves indicated that there was no apparent intestinal absorption of labeled IgGl from the milk in the period from 2 days to 3 wk. Furthermore, comparable decreases occurred in the specific activity of labeled IgGl in serum in the calves fed the labeled IgGl in colostrum at birth and subsequently maintained either on a diet including milk or on the synthetic milk diet devoid of IgGl. The results support the conclusion that the origin of new IgGl in the calf after about 36 h and up to about 3 wk of age arises from endogenous production at a rate of about 1 g of IgGl per day. © 1979, American Dairy Science Association. All rights reserved.