How to Manage Early Embryonic Death

During the past 20 years, per-cycle and per-season pregnancy rates have improved markedly in wellmanaged horse farms. By contrast, early embryonic death (EED) has remained a significant cause of frustration and economic loss, with approximately 15% of pregnancies detected at day 15 after ovulation failing to survive to term. Moreover, the majority ( 60%) of these losses occur before day 42 after ovulation, a period when pregnancy maintenance is critically dependent on progesterone produced by the primary corpus luteum (CL), and when a number of essential developmental events take place, including maternal recognition of pregnancy, embryogenesis and initial organogenesis, disintegration of the blastocyst capsule, endometrial cup formation, and the onset of definitive (chorio-allantoic) placenta formation. Despite its economic impact, surprisingly little is known about why EED occurs and whether, how and to what extent EED can be prevented. This is largely because EED is usually diagnosed retrospectively (ie, the conceptus has already disappeared or is obviously dying), when it is no longer possible to reliably establish the initiating cause. In addition, there has been a tendency to assume that the underlying problem is probably “progesterone insufficiency,” more because this is a deficit that can be addressed pharmacologically than because there is any real evidence to suggest that inadequate maintenance of CL function is a common cause of EED. Recently, there have been attempts to determine factors other than progesterone insufficiency that cause or predispose to EED.