Equine Prematurity and Dysmaturity – NAVLE Study Guide

Overview and Clinical Importance

Prematurity and dysmaturity represent critical conditions in equine neonatology that require immediate recognition and aggressive management. These foals are born with incomplete organ system development, rendering them unable to adapt to extrauterine life without intensive support. Understanding the distinction between prematurity, dysmaturity, and postmaturity is essential for accurate diagnosis and appropriate treatment planning.

The normal equine gestation ranges from 340 to 342 days, with significant individual variation (315-388 days). Final maturation of organ systems, particularly the hypothalamic-pituitary-adrenal (HPA) axis, lungs, and musculoskeletal system, occurs in the final weeks of gestation. Interruption of this maturation process results in foals that are "unready for birth."

Definitions and Classifications

Etiology and Risk Factors

Causes of Prematurity

Causes of Dysmaturity

• Placental insufficiency: Most common cause; results in chronic nutritional and oxygen deprivation
• Chronic placentitis: May allow mare to carry to term but impairs fetal development
• Twinning: Reduced placental surface area per fetus
• Endometriosis: Age-related degenerative changes reduce placental attachment
• Maternal undernutrition: Inadequate nutrient transfer to fetus

Causes of Postmaturity

Fescue toxicosis is the most common cause of postmaturity in horses. Ingestion of endophyte-infected tall fescue (Epichloë coenophiala, formerly Neotyphodium coenophialum) produces ergot alkaloids that inhibit prolactin secretion, leading to: