Maternal-fetal Blood Major Crossmatching in Merino Sheep.

To determine the incidence of ex vivo incompatibility between ovine maternal RBCs and fetal plasma, we performed cross-matching of blood samples from ewes and from lambs delivered by cesarean section. Twenty-one date-mated singleton pregnant Merino ewes were anesthetized for cesarean delivery of the fetus. At the time of delivery, paired maternal and fetal blood samples were collected and subsequently separated for storage as packed red blood cells and fresh frozen plasma. Gel column major cross matching was performed within 2 wk. All fetus-dam crossmatches were major crossmatches, combining fetal (recipient) plasma with dam (donor) RBCs. 172 individual dam-dam cross matches were performed. Two of these tests were incompatible (1.2%). In addition, 19 fetal blood samples collected immediately after cesarean delivery were crossmatched with 21 maternal samples to generate 174 maternal-fetal individual cross matches. No maternal-fetal incompatibility reactions were observed. The results of this study demonstrate that all maternal donors and fetal recipients were compatible. In addition, the incidence of an incompatible crossmatch between adult ewes was 1.2%. These data suggest that lambs may not be born with antibodies against other blood types, but rather may acquire such antibodies at some time during early life. In addition, these data suggest the risk of incompatibility reactions between ewes of a similar breed and from a single farm of origin is very low.