Intravenous (IV) describes anything located within, or introduced directly into, a vein. In equine medicine the intravenous route is the fastest and most reliable method of delivering fluids, electrolytes, and drugs to a horse's systemic circulation: a substance given IV reaches peak plasma concentration within seconds, compared with minutes (intramuscular) or hours (oral).
The external jugular vein, which runs in a groove along the neck between the the jugular groove running from poll to chest and the chest, is the standard IV access site in horses because it is large, superficial, and accessible. Emergency scenarios requiring rapid intravenous treatment include severe IV fluid therapy as a primary colic emergency response, septic hoof abscess in a compromised foal, and dehydration. IV catheters are placed for procedures requiring continuous fluid therapy or repeated drug administration, and must be maintained aseptically to prevent jugular thrombosis or infection. Only trained veterinary professionals should establish IV access in horses; incorrect placement or inadvertent injection of irritant drugs peri-vascularly can cause serious tissue necrosis.