Equine Retained Placenta and Placentitis – NAVLE Study Guide

Overview and Clinical Importance

Retained fetal membranes (RFM) and placentitis represent two of the most clinically significant reproductive conditions in equine practice. Retained placenta occurs when the fetal membranes fail to be expelled within 3 hours postpartum, and is considered a veterinary emergency due to the potential for life-threatening complications including metritis, laminitis, septicemia, and death. Placentitis, inflammation of the placenta typically due to ascending bacterial infection, is responsible for up to 30% of late-term pregnancy losses in mares. Understanding the pathophysiology, diagnosis, and treatment of these conditions is essential for NAVLE success and clinical practice.

Normal Equine Placental Anatomy

The equine placenta is classified as diffuse, microcotyledonary, and epitheliochorial. This means the entire surface of the chorioallantois attaches to the endometrium through millions of microscopic finger-like projections called microcotyledons, and six tissue layers separate maternal and fetal circulations. This placental arrangement has critical clinical implications.

Key Anatomical Features and Clinical Significance

Placental Examination: The F-Shape Method

Every placenta should be examined immediately after expulsion. Lay the membranes out in an "F" shape with the chorionic (red, velvety) surface exposed. The bottom leg represents the cervical end with the cervical star rupture site. The vertical portion corresponds to the uterine body. The upper arm (longer, thicker) represents the gravid horn, and the lower arm (thinner, wrinkled) represents the nongravid horn. Normal placental weight should be approximately 11% of foal body weight.