Absorption and half-life of bovine, caprine and ovine IgG1 in the newborn lamb. Effect of experimental prematurity and endocrine factors.

The influence of experimental prematurity and endocrine factors on the absorption and half-life of bovine IgG1 was studied in newborn Limousin x Romanov lambs. Six preterm and six full-term animals were bottle-fed with a common bovine colostrum pool during 32 h, whereas seven preterm and six full-term lambs were fed with the same bovine colostrum 2 h post-partum, a caprine colostrum 8 h after birth and an ovine colostrum 16 h post-partum. In the first group, the maximal plasma IgG1 levels were not affected by experimental prematurity; however, the duration of the Ig absorption period seemed to be longer in preterm lambs. In the second group, absorption of blgG1 given at the first feeding was depressed in experimental preterm animals, whereas no difference remained for clgG1 given at the second feeding, and at the third feeding, olgG1 were better absorbed than in full-term lambs. This set of data indicates that the duration of the Ig absorption period was longer in preterm than in full-term lambs. The results obtained confirm the importance of thyroid function for acquisition and maintenance of passive immunity : plasma T4 levels were negatively related to the maximal plasma IgG1 levels in the first group of lambs, and positively related to the half-life of IgG1 in all animals. On the other hand, cortisol was negatively related to IgG1 absorption, at least during the first hours of life. The half-life of clgG1 in the plasma of the lambs was not modified by experimental prematurity, and was no different from the half-life of blgG1 in preterm lambs. However, the half-life of blgG1 was significantly lower in full-term than in preterm animals. This observation suggests that a mechanism of recognition of heterologous IgG1 could mature during the last 9 days of gestation.