A racing start in life? The hurdles of equine feto-placental pathology.

Significant progress has been made in understanding and monitoring the causes of equine abortion over past decades. However, not all in utero pathology results in abortion. It has long been recognised that some in utero pathology, such as twinning or chronic placentitis, can result in the birth of live but growth-retarded foals and there is historical evidence that birth weight may influence future athletic performance. Clinical experience (e.g. from twins) and experimental studies (pony-Thoroughbred embryo transfer) have highlighted the importance of reduced functional placental area in limiting growth in utero in horses. Many other nonfatal in utero pathologies (e.g. umbilical cord-related circulatory compromise) can potentially affect either placental function or other organ systems. Their influence on the short- and long-term health of the foal and its future athletic performance is in many cases poorly documented or understood. This review summarises the main causes of in utero pathology and reflects on how these may potentially affect the foal if born alive, highlighting the need for long-term studies on this important subject.