The interaction of homologous and heterologous IgG during intestinal absorption was investigated using five groups of newborn piglets (50 animals in total). The diet, given via a stomach tube, was different in each group during the first 24 h. Group I received bovine colostrum, group II bovine colostrum and porcine IgG solution, group III bovine and porcine colostrum, group IV bovine colostrum and intraperitoneally applied monomeric porcine IgG, and group V received a glucose diet with no immunoglobulins. Feeding was based on bovine colostrum between the 2nd and 6th days after birth, followed by a milk replacer during the rest of the experimental period. The serum concentrations of homologous and heterologous IgG were monitored from birth to 10 weeks of age. The total serum IgG content (homologous + heterologous) of newborns was almost equal in groups I-IV at 24 h. Porcine IgG from endogenous synthesis was detectable in the serum of groups I and V two weeks postpartum. The heterologous IgG absorbed from bovine colostrum produced nearly the same serum concentration in groups II and III: hence the different components of porcine colostrum did not influence the absorption of heterologous IgG. Intraperitoneal application of 1.3 g porcine IgG in group IV resulted in a delay of the synthesis of endogenous IgG. The average half-life of heterologous IgG in the serum of groups I-IV was almost exactly the same, showing that the porcine colostrum or IgG solution did not modify the half-life of bovine IgG. The ingestion of the glucose diet within the first 24 h completely blocked the absorption of IgG from bovine colostrum applied from the second day. Possible explanations of the phenomena investigated are discussed.
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