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

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Author: Doug Thal DVM Dipl. ABVP


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