Maternal dexamethasone treatment in late gestation induces precocious fetal maturation and delivery in healthy Thoroughbred mares

Summary Reasons for performing study: The foal requires an active hypothalamo‐pituitary‐adrenal (HPA) axis for organ maturation and post natal survival. Prenatal administration of synthetic glucocorticoids may provide an effective method for inducing fetal maturation safely in the mare. Objectives: To determine whether dexamethasone administered to late pregnant mares: 1) will induce fetal maturation and precocious delivery; 2) is safe to use and 3) to identify endocrine responses in the mare and foal. Methods: Pregnant Thoroughbred mares received either 100 mg dexamethasone i.m. (treated n = 5) or 50 ml saline i.m. (control n = 5) at 315, 316 and 317 days of gestation. Plasma progestagens, cortisol and prostaglandin F2α metabolite (PGFM) concentrations were measured before and after treatment. The foals were weighed, the crown‐rump length (CRL) measured and an adrenal stimulation test performed on Day 1. Results: Dexamethasone significantly (P