[The spontaneous reduction of a twin pregnancy in two mares]

Twin pregnancies are a serious problem in stud medicine as they terminate in most cases in abortion, stillbirth or the delivery of dead or weak and deformed foals. In recent years, the introduction of sonography has greatly improved the management of mares with twin conceptuses, in particular monitoring the phenomenon of spontaneous embryo reduction to a single vesicle. This allows supervision of pregnancy with relatively little expenditure and loss of time. We document the spontaneous reduction to single vesicles of unilateral twin pregnancies in a draught- and a warmblood-mare. In both mares diagnosis of twins was made 17 days after covering; they probably resulted from synchronous double-ovulations. After another 5 days, distinct signs of the loss of one conceptus were recognized and, subsequently, only single pregnancies existed. No interventions were necessary.