ARS/FAPRU: Effects of Domperidone on Peripheral Vasoconstriction and Prolactin Concentrations in Horses Grazing Toxic Kentucky 31 Tall Fescue

There are approximately 7.2 million horses in the U.S. [1]. Kentucky has over 242,000 horses, with the state’s equine industry estimated at over $23 billion [2]. Tall fescue, Lolium arundinaceum (Schreb.) Darbysh., occupies over 34 million acres in the U.S. alone [3], with most of that in the Eastern U.S., and fescue is found in about 5½ million acres in Kentucky. Over 1 million of those acres in Kentucky are devoted specifically for equine use, so it is not surprising that the majority of horses in Kentucky, and in the Eastern U.S., may be exposed to tall fescue at some point in their lives. Most of the tall fescue is infected with a fungal endophyte, Epichloë coenophiala, which produces chemicals (alkaloids) that are harmful to grazing animals, with ergovaline being the most abundant of those alkaloids [4-8]. Pregnant mares grazing toxic tall fescue, such as Kentucky 31 (KY31) frequently incur problems in late pregnancy such as extended gestation, thickened placenta, dystocia, agalactia, and potentially death of the foal and/or mare at parturition [9-11]. Historically, the endocrine hallmark of fescue toxicosis in several species, including horses, has been the decrease in circulating concentrations of prolactin [9,13], and it is this reduced prolactin that results in agalactia.