Early Embryonic Loss in the Mare

Abstract

INTRODUCTION Early embryonic loss in the mare is generally defined as pregnancy failure that occurs between fertilization and day 40 to 60 of gestation. The diagnosis of early embryonic loss and recognition of factors contributing to its occurrence have been dramatically improved by the routine use of transrectal ultrasonography for early pregnancy diagnosis. Under field conditions, transrectal ultrasonography is typically used for an initial pregnancy diagnosis as early as day 12 to 14 post-ovulation, whereas under experimental conditions it may be used as early as day 10 or 11; therefore, ultrasonography allows direct (and repeatable) assessment of the conceptus during approximately three quarters of the interval when early embryonic loss occurs. Prior to day 10, the conceptus is too small to be visualized with standard ultrasonographic equipment, therefore other techniques have been used to study embryonic loss during that interval. Specifically, clinical procedures such as embryo transfer and oocyte transfer and experimental techniques such as in vitro embryo culture and light/electron microscopy of oocytes/embryos have been used to study early embryonic loss prior to day 10.