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

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Author: Doug Thal DVM Dipl. ABVP


    We're not around right now. But you can send us an email and we'll get back to you, asap.