Inflammation is the localized protective response of vascular connective tissue to injury, infectious trigger driving the response, or irritants. It is a fundamental biological mechanism, not a disease in itself: the five cardinal signs recognized since antiquity—heat (calor), pain (dolor), swelling (tumor), redness (rubor), and loss of function (functio laesa)—are the outward expression of increased blood flow, vascular permeability, and the migration of immune cells to the site of insult. In horses these signs appear across a wide spectrum of conditions: a hot, swollen fetlock joint from a minor sprain, a painful abscess in the hoof, an inflamed tendon sheath (tenosynovitis), or the systemic inflammatory cascade of endotoxemia.
The process unfolds in sequence. Tissue injury releases damage-associated molecular patterns (DAMPs) that activate resident mast cells and macrophages; these cells release vasoactive mediators—histamine, prostaglandins, and bradykinin—that dilate local blood vessels and increase capillary permeability. Protein-rich plasma leaks into the interstitium (producing the swelling), neutrophils emigrate from dilated vessels within minutes to hours and begin phagocytosing bacteria or cellular debris, and monocytes follow over the subsequent twenty-four to forty-eight hours to sustain the response and initiate repair. Prostaglandins, particularly PGE2, sensitize pain receptors at the site and act on the hypothalamus to raise body temperature (see hyperthermia), creating the fever associated with acute systemic inflammatory states.
In equine clinical practice, management of acute inflammation relies primarily on non-steroidal anti-inflammatory drugs (NSAIDs)—phenylbutazone (bute) and flunixin meglumine (Banamine) being the most widely used—which inhibit cyclooxygenase enzymes and reduce prostaglandin synthesis. Cold therapy (icing or cold-hosing) applied in the first twenty-four to forty-eight hours of an acute soft-tissue injury limits the initial vascular response and reduces pain. Rest and controlled loading protect the inflamed tissue from further mechanical damage while repair proceeds. Chronic inflammation in which the resolution phase fails—as in some tendon, joint, and airway conditions—may require corticosteroid treatment, targeted regenerative therapies (PRP, IRAP), or management of the underlying trigger such as airway conditions where resolution fails. The body condition of the horse is a relevant variable because adipose tissue in obese horses secretes pro-inflammatory adipokines that sustain low-grade systemic inflammation and worsen conditions such as insulin dysregulation and laminitis.
Further Reading
- inflammation (Wikipedia)
- For broader reading on inflammatory joint conditions: joint disorders in horses — MSD Veterinary Manual