Studies on fetal physiology in the sheep: Transplacental passage of antibodies and techniques for repeated sampling of the fetal lamb in situ

Abstract

To determine whether antibodies could be transferred from the maternal to the fetal side of the placenta, blood and amniotic fluid were obtained from 5 pregnant ewes and their fetal lambs. This was done during the last trimester of pregnancy, with the ewes under general anesthesia, before and after immunization of the ewes against Salmonella pullorum. Pregnancy was not interrupted. An additional 5 pregnant ewes were used to study antibody transfer in the opposite direction. The ewes in the latter group and their fetal lambs were successfully sampled before treatment; however, all of these pregnancies were interrupted because of the toxicity of the S. pullorum antigen or antibodies given to the fetuses.Transfer of S. pullorum antibodies across the sheep placenta could not be demonstrated in the mother-to-fetus direction. Results are inconclusive regarding the possibility of antibody transfer in the fetus-to-mother direction. It was not possible to develop an antibody pressure on the fetal side.Surgical techniques were developed to permit entering and re-entering the gravid uterus of the sheep during the last trimester of pregnancy without terminating pregnancy or impairing the viability of the fetus. Two ewes, each subjected to 2 successive hysterotomies at an interval of about 20 days, were delivered of live lambs with no complications, by natural birth, 12 and 23 days after the last operation, and they raised their lambs successfully.