To inject is to mechanically force a substance into living tissue or a body cavity using a needle, cannula, or syringe. In equine veterinary practice, injection bypasses the gut entirely, allowing drugs to act faster and at more predictable blood concentrations than oral administration. The primary injection routes in horses are intramuscular (IM), IV route compared (IV), and subcutaneous (SQ), each suited to specific drug formulations and clinical urgencies.
Common substances injected in horses include vaccines (see common injection context), antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs), sedatives, and joint therapies such as corticosteroids or hyaluronic acid. Safe injection technique requires sterile needles, correct site selection, aspiration to confirm needle placement, and rotation of IM sites to prevent local muscle damage or abscess formation. Accidental intra-arterial injection of irritant substances is a serious emergency.
Further Reading
Injection as a route of medication delivery is explained in the injection (medicine) article on Wikipedia. Guidance on how injectable treatments are administered in horses is provided in the Merck Veterinary Manual section on Routine Care and Breeding of Horses.