Investigation of some factors which influence the absorption of IgG by the neonatal piglet

Abstract

The absorption by the neonatal gut of purified swine IgG isolated from maternal serum was studied in 91 motherless piglets raised without swine colostrum, to investigate some of the factors which influence absorption. Factors studied included the amount of IgG administered, the effect of bovine colostrum fed concurrently, the influence of starvation and the effect of lactose. Administration of iodinated IgG within 3 hours after birth resulted in the appearance of IgG in the piglet circulation in unaltered form. Immediate feeding of bovine colostrum followed by administration of iodinated IgG at 72 hours resulted in the appearance of only IgG digestion fragments in the circulation. Administration of 15 g of lactose during the first 24 hours reduced absorption of IgG by 26% compared to controls while treatment with 54 g of lactose reduced absorption by 94%. On the contrary, when bovine colostrum was administered immediately after purified IgG, the amount of swine IgG absorbed was 50–70% greater than in controls. Mature milk failed to have the same influence. Finally, in experiments in which the amount of purified swine IgG administered varied from 1.0 to 8.0 g, absorption was directly proportional to the amount administered. When these data were compared with data on naturally reared piglets, the same proportionality was seen and indicated a consistent 1:2.5 to 1:3 ratio of ingested IgG (g) to the maximal serum level of immunglobulin (mg/ml) resulting from absorption. IgA and IgM follow a similar pattern. The data are consistent with a regulated absorption mechanism, that appears to be lost very quickly after the initial ingestion of food. Heterologous protein and lactose alone can switch off this absorption mechanism, thus arguing against “gut closure” by a mechanism of receptor saturation by absorbed IgG. Bovine colostrum, when compared to mature milk, is able to augment the absorption of swine IgG by an unknown mechanism.