Horse Side Vet Guide ®

Equine Health Resource

Depressed, Dull, Sick or Lethargic

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

Code Orange - Call Your Vet at Their First Available Office Hours

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

  • If the horse has no appetite and is obviously depressed.
  • If you notice other signs of abdominal pain (colic).
  • If the results of the Whole Horse Exam (WHE) in the resting horse indicate fever (Temp>101F/38.3C), or heart rate greater than 48 BPM.

Code Orange - Call Your Vet at Their First Available Office Hours

    Horses are usually very active and alert animals. When a horse seems depressed, there is often an underlying reason. Keep in mind that “depressed” may mean a variety of things – sleepy or drowsy seeming, head hanging, lip hanging, usually not eating. A horse may uncharacteristically stand in a corner, not interested in you, other horses or in the environment.

    I want to mention donkeys here too, because they express pain and illness quite differently than horses do. Donkeys in pain tend not to be as expressive, more stoic. Like horses, sick or painful donkeys don’t eat. A few specific behaviors that ill or painful donkeys exhibit include closing the eyes for long periods, appearing to doze on their feet, and lowering their heads. Mules tend to be somewhere in the middle in terms of how they express pain and illness.

    In hot weather, a warm winter afternoon, or at times during the middle of the day, healthy horses may simply stand quietly with their head hanging down, as normal behavior.

    Depression, dullness or sickness (a/k/a “ain’t doing right” – ADR) is a very common complaint that can result from a huge variety of underlying causes. Illnesses can cause pain or affect body systems, and can result in behavioral changes.

    Taken alone, depression is usually too broad a sign to help your vet narrow down the problem. However, depression or lethargy in horses is often accompanied by other abnormalities that, taken together, assist your vet in choosing appropriate diagnostics, reaching a diagnosis, and suggesting treatment options. By being an astute observer of your horse, you may notice additional signs that help determine the need for veterinary intervention.


    If you notice that your horse (or other equine) is depressed or lethargic, that is a good starting point for additional observation. Take some time to carefully watch them and assess the environment for any other clues. Offer feed and judge response. Hand walking straight and to both small circles is another good way to evaluate attitude and movement. Assess your equine’s general health using the Whole Horse Exam (WHE), and share your findings and concerns with your vet.


    Your vet will usually start with a careful history, and then will carefully examine the horse, looking for signs that give clues to the nature of illness. Depending upon those findings, they may suggest blood work or other diagnostics to help better understand the nature of the problem.

    Identify or Rule-Out Possible CausesDIAGNOSES

    Colic, Undiagnosed Conditions Causing
    Pneumonia, Pleuropneumonia & Pleuritis, Generally
    Viral Infection, Non-Specific
    Duodenitis-Proximal Jejunitis, DPJ
    Viral Upper Respiratory Tract Infections, Generally
    Clostridial, Clostridium Colitis (in Adult)
    Equine Gastric Ulcer Syndrome, EGUS (in Adult)
    Large Colon Impaction, Pelvic Flexure Impaction
    Kidney Failure, Acute Renal Failure
    Kidney Failure, Chronic Renal Failure
    Red Maple Leaf Toxicosis
    Poisonous Snake Bite, Rattlesnake or Pit Viper
    Endotoxemia, Endotoxic Shock
    Anemia, Generally
    Pigeon Fever
    Small Strongyle Infestation
    West Nile Virus, WNV
    Acute Respiratory Distress Syndrome, ARDS
    Equine Influenza, EI
    Potomac Horse Fever, Neorickettsiosis
    Ascarid Worm Impaction
    Small Intestinal Strangulation, Pedunculated Lipoma
    Abdominal or Internal Abscess, Generally
    Hypoglycemia, Low Blood Sugar
    Equine Herpesvirus 1 & 4, Rhinopneumonitis
    Salmonella Colitis (in Growing Foal or Adult)
    Liver Failure, Generally
    Metritis, After Foaling
    Intra-Muscular Injection Site Reaction
    Bastard Strangles
    Cholangiohepatitis, Cholelithiasis
    Intestinal Lymphosarcoma
    Aflatoxicosis, Aflatoxins
    Purpura Hemorrhagica, PH
    Equine Granulocytic Ehrlichiosis, EGE
    Lyme Disease, Borreliosis
    Eastern, Western & Venezuelan Equine Encephalomyelitis
    Hyperlipemia, Lipemia
    Pyrrolizidine Alkaloid Plant Toxicity
    Ileal Impaction
    Colic, Simple Intestinal Gas or Spasm
    Equine Infectious Anemia, EIA
    Carbohydrate or Grain Overload
    Colic, Gas, Large Colon Tympany
    Lead Poisoning
    Conditions or Diagnoses, Generally
    Renal Tubular Acidosis, RTA
    Insect Stings, Centipede, or Spider Bites
    Equine Anaplasmosis
    Theiler's Disease, Serum Hepatitis or Sickness
    Adhesions, Intra-Abdominal
    Protein-Losing Intestinal Diseases, Generally
    Choke, Esophageal Feed or Foreign Body Obstruction
    Clostridial Myositis
    Intestinal Foreign Body
    Sedation Effects
    Neoplasia, Tumor or Cancer, Stomach
    Blister Beetle Toxicity
    Hepatic Encephalopathy
    Cecal Disorders, Generally
    Infarcted Intestine or Colon
    Bacteremia, Septicemia (in Adult)
    Moldy Corn Toxicity
    Equine Piroplasmosis, EP
    Ergot Toxicity
    Granulomatous Gastrointestinal Disease
    Selenium Toxicity
    Enteroliths, Intestinal Stones
    Japanese Encephalitis
    Liver Abscess
    Retained Placenta
    Fracture of Incisive Bone of Upper Jaw or Mandibular Incisors Lower Jaw
    Fracture of Skull, Involving Sinus or Bone
    Abscessed or Infected Molar, Periapical Abscess
    Fracture of Skull, Not Involving Sinus
    Monensin Toxicity
    Equine Proliferative Enteropathy, EPE
    Equine Herpes Myeloencephalitis, EHM
    Conditions Affecting Red Blood Cells, Generally
    Vesicular Stomatitis, VS
    Pemphigus Foliaceus
    Cardiotoxic Plants, Generally
    Coronavirus Entero-Colitis
    Locoweed Toxicity
    Neoplasia, Tumor or Cancer, Kidney
    Neoplasia, Tumor or Cancer, Brain
    Neoplasia, Tumor or Cancer, Thorax
    Nitrate Toxicity
    Neoplasia, Tumor or Cancer, Liver
    Abscess Near Anus, Vulva or Tail Base
    Neoplasia, Tumor or Cancer, Sinus or Nasal Passage
    Rodenticide Toxicity, Generally
    Buttercups Toxicity
    White Snakeroot Toxicity
    Stomach Outflow Obstruction
    Congestive Heart Failure, CHF
    Liver Disease, Acute Hepatitis
    Fractured or Broken Ribs (in Adult)
    Equine Motor Neuron Disease, EMND
    Stress or Anxiety, Generally
    Water Hemlock Toxicity
    Pulmonary Edema
    Temporohyoid Osteoarthropathy
    Smoke Inhalation, Pneumonitis
    Horsetail or Bracken Fern Toxicity
    Equine Viral Arteritis, EVA
    Rectal Tear
    Kidney & Ureteral Stones
    Blue Green Algae Toxicity
    Black Locust Tree Toxicity
    Ruptured Aorta, Ruptured Aortic Aneurysm
    Leukemia, Cancer, Blood or Bone Marrow
    Guttural Pouch Mycosis
    Diaphragmatic Hernia, Ruptured Diaphragm
    Foal Heat Diarrhea (1-2 Weeks of Age)
    Acorn & Oak Bud Toxicity
    Trypanosomiasis, Surra, Mal de Caderas
    Pyrethrin Toxicity
    Borna Disease
    Blue Weed, Patterson's Curse Toxicity
    Infectious Myelitis
    Internal Ear Infections
    Mare Reproductive Loss Syndrome, MRLS
    Hemlock Toxicity
    Jimsonweed Toxicity
    Neuroaxonal Dystrophy, NAD
    Clotting Factor Deficiency, Coagulation Problem
    Bile Stones
    Arsenic Toxicity
    Anhidrosis, Dry Coat Syndrome
    Phenothiazine Toxicity
    Morning Glory Toxicity
    Amitraz Toxicity
    African Horse Sickness, AHS
    Adrenal Insufficiency
    Foal or Newborn, Combined Immunodeficiency, CID
    Hoary Alyssum Toxicity
    Lupine Toxicity
    Marijuana Toxicity
    Oleander Toxicity
    Conjunctivitis, Generally
    Plant or Weed Toxicity, Generally
    Equine Grass Sickness
    Diabetes Mellitus

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Author: Doug Thal DVM Dipl. ABVP


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