First record of abortion of single co-twin in an Arabian mare and continuity of the other to full term and birth

Twin pregnancies in Arabian horses is a major cause of abortion. In all cases when the abortion occurs, it occurs for both fetuses. Unusually in the case described here, which we believe has not previously been documented in Arabian horses, one fetus aborted in undersized and representing an age of 4 months. The other fetus completed the gestation and reached full term followed by birth. The authors postulated that one fetus underwent a stage of diapause like marsupials in a blastocyst stage then re-grew again, followed by abortion. The parentage analysis confirmed that both feti are derived from the same dam and sire stallion.