Horse Side Vet Guide ®

Equine Health Resource

Fever, Rectal Temperature Greater than 101.5 (in Adult)

Code Red - Call Your Vet Immediately, Even Outside Business Hours

Code Red - Call Your Vet Immediately, Even Outside Business Hours

    Fever is caused by a center in the hypothalamus of the brain changing the set point for the body’s normal temperature. Fever has an important purpose in fighting infection and should not always be reduced. All fevers should be monitored, but not all of them should be treated.

    A normal temperature for an adult horse is 98-101 degrees Fahrenheit. A mild elevation in temperature (up to 102 degrees F) can be due to a trailer ride in hot weather, recent exercise, or excessive blanketing. It is also a classic indication of the immune system responding to viral or microbial infection.


    Assess the horse’s general health using the Whole Horse Exam (WHE), paying particular attention to their attitude and appetite, and look for other signs of illness.

    If your horse has a mild fever or you believe that it may be transient (related to exercise or trailering in hot weather), you can monitor the horse and reassess their temperature in an hour.

    However, if the fever persists or your horse is showing other signs of illness, you should immediately contact your vet to discuss your findings and concerns.


    Your vet will start with a careful history, considering the predisposing factors. Of particular interest to us is recent travel and exposure to other horses. A physical exam suggests body systems involved and blood work and other diagnostics help refine the diagnosis.

    Identify or Rule-Out Possible CausesDIAGNOSES

    Viral Upper Respiratory Tract Infections, Generally
    Viral Infection, Non-Specific
    Equine Influenza, EI
    Retained Placenta
    Equine Herpesvirus 1 & 4, Rhinopneumonitis
    Clostridial, Clostridium Colitis (in Adult)
    Exhausted Horse Syndrome, EHS
    Endotoxemia, Endotoxic Shock
    West Nile Virus, WNV
    Equine Herpes Myeloencephalitis, EHM
    Bacteral Infection, Generally
    Pigeon Fever
    Metritis, After Foaling
    Duodenitis-Proximal Jejunitis, DPJ
    Cholangiohepatitis, Cholelithiasis
    Abscess in Any Location, Generally
    Sole, Foot or Hoof Abscess
    Abdominal or Internal Abscess, Generally
    Bastard Strangles
    Equine Infectious Anemia, EIA
    Pneumonia, Pleuropneumonia & Pleuritis, Generally
    Eastern, Western & Venezuelan Equine Encephalomyelitis
    Potomac Horse Fever, Neorickettsiosis
    Blister Beetle Toxicity
    Vesicular Stomatitis, VS
    Equine Anaplasmosis
    Carbohydrate or Grain Overload
    Jugular Vein Thrombosis
    Equine Rhinitis A & B Viruses
    Nail or Other Foreign Body Punctures Foot, Sole or Frog
    Purpura Hemorrhagica, PH
    Equine Granulocytic Ehrlichiosis, EGE
    Hendra Virus, HeV
    Heat Exhaustion or Stroke
    Salmonella Colitis (in Growing Foal or Adult)
    Equine Viral Arteritis, EVA
    Acute Respiratory Distress Syndrome, ARDS
    Lyme Disease, Borreliosis
    Smoke Inhalation, Pneumonitis
    Right Dorsal Colitis
    Clostridial Myositis
    Vasculitis, Generally
    Anhidrosis, Dry Coat Syndrome
    Abscess Near Anus, Vulva or Tail Base
    Insect Stings, Centipede, or Spider Bites
    Bacteremia, Septicemia (in Adult)
    Coronavirus Entero-Colitis
    Meningo-Encephalitis, Meningitis
    Pemphigus Foliaceus
    Infarcted Intestine or Colon
    Aflatoxicosis, Aflatoxins
    Liver Abscess
    Brucellosis, Poll Evil, Fistulous Withers
    Ascarid Worm Impaction
    Malignant Hyperthermia
    Infectious Myelitis
    Equine Piroplasmosis, EP
    Intestinal Lymphosarcoma
    Temporohyoid Osteoarthropathy
    Rectal Tear
    Ulcerative Lymphangitis
    Shoe Boil, Olecranon Bursitis
    Phenothiazine Toxicity
    Hoary Alyssum Toxicity
    Plant or Weed Toxicity, Generally
    Mare Reproductive Loss Syndrome, MRLS
    Navicular Bursa Penetrated by Foreign Body
    Trypanosomiasis, Surra, Mal de Caderas
    Japanese Encephalitis
    Guttural Pouch Empyema & Chondroids
    Hypocalcemic Tetany
    African Horse Sickness, AHS
    Headshaking Syndromes, Generally
    Austrailian Bat Lyssavirus, ABLV
    Ivermectin Toxicity

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Author: Doug Thal DVM Dipl. ABVP


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