sickhorses

Month: June 2026

  • Anhidrosis in Horses: When a Horse Cannot Sweat

    Anhidrosis — the partial or complete inability to sweat normally — is a serious thermoregulatory failure. Evaporative cooling through sweating accounts for approximately 65% of heat loss during exercise. When a horse stops sweating, internal temperature climbs rapidly with any exertion. The condition is most common in horses moved to hot, humid climates.

    Causes

    The dominant hypothesis involves exhaustion of sweat gland function through chronic overstimulation. Horses moved to hot, humid regions are at highest risk. Johnson et al. (1998) demonstrated reduced sweating response to exogenous epinephrine in anhidrotic horses, supporting beta-adrenergic receptor downregulation as the mechanism.

    Clinical Signs

    • Absent or markedly reduced sweating despite heat and exercise
    • Dry, rough, or dull coat; some horses lose facial hair — coat changes in hot climates warrant ruling out Cushing’s disease and equine metabolic syndrome as contributing factors
    • Distressed respiratory pattern: rapid, labored breathing in heat
    • Elevated resting temperature: commonly 38.5 to 40 degrees C
    • Exercise intolerance: rapid fatigue
    • Partial anhidrosis: flank and axilla retain sweating while neck and back remain dry

    Management

    No treatment is reliably curative. Moving the horse to a cooler climate is the most effective approach; many horses recover spontaneously within 1 to 3 months. Work horses during the coolest part of the day. Maximize ventilation with fans and shade. Water misting over a fan increases evaporative cooling substantially. Active cooling after exercise is essential: sponge with cool water and scrape repeatedly — see our full guide to summer heat management.

    Supplementation: One AC (acetyl L-carnitine) is anecdotally reported to restore sweating in some horses. Dark beer has been used in Gulf Coast barns with anecdotal benefit. Neither has strong controlled trial evidence.

    Monitoring and Prognosis

    Do not exercise if baseline temperature exceeds 38.8 degrees C. Monitor for signs of dehydration, which compound heat stress. Heat stroke (rectal temperature above 41 degrees C, staggering, muscle fasciculations) requires immediate veterinary attention. Horses remaining in hot, humid environments may continue to be anhidrotic indefinitely, but with careful management most can remain in moderate work.

    Sources: Johnson PJ et al. Vet Clin North Am Equine Pract 2002; Johnson PJ et al. J Vet Intern Med 1998; AAEP Endocrinology Guidelines (aaep.org).

  • Pigeon Fever in Horses: Causes, Abscesses, and Treatment

    Pigeon fever — named for the chest swelling that gives affected horses a pigeon-breast appearance — is caused by Corynebacterium pseudotuberculosis. Originally a disease of the arid western US, reports have increased in frequency and geographic range. Huber et al. (J Vet Intern Med 2016) confirmed temperature, drought conditions, and fly season length as the strongest predictors of outbreak intensity in California.

    Three Forms

    External abscesses (approximately 75%): large, firm, warm swellings on the chest, ventral midline, or hindlimbs. Abscesses grow over days to weeks, eventually softening and rupturing. Affected horses are febrile (39 to 40 degrees C) and depressed during active development.

    Internal abscesses (approximately 8 to 10%): form in liver, spleen, or lungs. Horses present with weight loss, fever of unknown origin, and internal pain without external swellings. Guarded to poor prognosis.

    Ulcerative lymphangitis: recurring ulcerative nodules along lower limb lymphatics with marked swelling. Risk of permanent lymphatic damage.

    Treatment: External Abscesses

    Primary treatment is drainage, not antibiotics. Antibiotics withheld because (1) thick capsule limits penetration, (2) premature use impairs maturation.

    1. Monitor daily for maturation: softening, fluctuance, and visible point
    2. Hot pack twice daily for 20 to 30 minutes
    3. Surgical drainage when mature; ensure complete evacuation
    4. Lavage with dilute chlorhexidine or povidone-iodine; avoid hydrogen peroxide
    5. Maintain dependent drainage; Penrose drain if needed
    6. NSAIDs for pain and fever

    Most external abscesses resolve within 3 to 6 weeks. Horses are not immune after infection. Antibiotics (penicillin or trimethoprim-sulfonamide) indicated for internal disease or ulcerative lymphangitis.

    Biosecurity

    Isolate affected horse. Dispose of drainage material; do not compost. Disinfect with bleach (1:32) or quaternary ammonium compounds. Implement insect control. No commercial vaccine available in the US.

    Sources: Huber L et al. J Vet Intern Med 2016; Pringle JK et al. in Equine Infectious Diseases, 2nd ed. (2014).

  • Equine Recurrent Uveitis: The Leading Cause of Blindness in Horses

    Equine recurrent uveitis (ERU) is the most common cause of blindness in horses worldwide. It is an immune-mediated inflammatory disease of the uveal tract — iris, ciliary body, and choroid — cycling through painful, vision-threatening episodes. Each episode causes cumulative damage.

    Causes and Risk Factors

    Leptospira interrogans (serovars Pomona and Grippotyphosa) is strongly associated with ERU in the US. Appaloosa horses have a 25-fold increased risk; the LP (leopard complex) allele (PATN1, TRPM1 loci) is associated with ERU susceptibility. Warmbloods are also overrepresented.

    Clinical Signs of a Flare-Up

    • Blepharospasm: squinting — the most obvious sign
    • Epiphora: excessive tearing
    • Photophobia: sensitivity to bright light
    • Corneal cloudiness or haze: bluish-white opacity
    • Miosis: constricted, pinpoint pupil
    • Aqueous flare: haziness in the anterior chamber

    Treatment

    Topical atropine 1% prevents synechiae; overuse reduces gut motility. Topical corticosteroids reduce intraocular inflammation — contraindicated if corneal ulcer present. Systemic NSAIDs reduce pain during a flare.

    Surgical options: intravitreal cyclosporine implant (sustained release 3 to 4 years; Gilger et al., Vet Ophthalmol 2010 showed significant flare reduction); pars plana vitrectomy (removes vitreous and Leptospira; excellent results in Warmbloods per Becker et al.); enucleation for non-visual painful eyes.

    When to Call the Vet

    Call immediately if you notice squinting, cloudiness, excessive tearing, or any eye change. Equine uveitis is never watch-and-see.

    Sources: Gilger BC et al. Vet Ophthalmol 2010; Becker M et al. Vet Ophthalmol 2008; Knottenbelt DC, Pascoe RR. Diseases and Disorders of the Horse (2003).

    For deeper question-and-answer context on equine eye health and systemic conditions that affect vision, see horse-info.org.

  • Equine Influenza: Symptoms, Vaccination, and When to Call the Vet

    Equine influenza (EI) is caused by influenza A virus strains H3N8 and H7N7, with H3N8 responsible for virtually all contemporary outbreaks. It spreads via respiratory aerosols and contaminated equipment. The OIE Expert Surveillance Panel monitors strain evolution and issues biannual vaccine composition recommendations. Current AAEP guidelines recommend vaccines matching OIE recommendations.

    Clinical Signs

    • Fever: 38.5 to 41 degrees C, often the first sign
    • Dry, harsh cough: persistent, may last 2 to 3 weeks
    • Nasal discharge: watery initially, may thicken with secondary infection
    • Depression and anorexia

    Treatment

    Rest is the most critical intervention — one week of rest per day of fever. NSAIDs reduce fever. Antibiotics not indicated unless secondary bacterial pneumonia develops. Isolate affected horses immediately.

    Vaccination

    AAEP recommends biannual vaccination for horses with regular contact with other horses. Modified live intranasal vaccines (Flu Avert, Merck) stimulate local mucosal immunity. Killed virus intramuscular vaccines require a two-dose primary series then 6-month boosters. New arrivals should be isolated 3 weeks before joining the herd.

    Biosecurity During an Outbreak

    Isolate affected horses immediately. Restrict horse movement. Use separate equipment; handlers wash hands between barns. Monitor all horses for fever twice daily for 10 to 14 days (the same protocol used when managing strangles outbreaks).

    Prognosis

    Excellent for uncomplicated disease with adequate rest. Prognosis worsens with premature return to work or secondary bacterial pneumonia.

    Sources: AAEP Infectious Disease Guidelines; OIE Expert Surveillance Panel; Pusterla N et al. in Equine Infectious Diseases, 2nd ed. (2014).

  • Equine Sarcoids: Types, Diagnosis, and Treatment Options

    Equine sarcoids are the most common skin tumor in horses worldwide, accounting for approximately 40% of all equine neoplasms (Knottenbelt, Equine Vet J, 2019). They can appear on any horse at any age, are locally invasive, and have a strong tendency to recur after treatment. Despite decades of research, they remain one of the most clinically challenging conditions in equine medicine — not because they are fatal, but because they are difficult to eliminate permanently and can cause significant welfare and performance issues.

    What Are Equine Sarcoids?

    Sarcoids are locally aggressive, fibroblastic skin tumors. They do not typically metastasize to internal organs, but they grow, ulcerate, and invade local tissues. The cause is strongly linked to bovine papillomavirus (BPV) types 1 and 2 — though the virus alone does not explain distribution (flies are implicated as mechanical vectors; genetic susceptibility via MHC class II genes plays a role). They cannot spread between horses via normal contact, but wound sites and previous sarcoid locations are at elevated risk of new lesions.

    The Six Clinical Types

    Sarcoids present in six recognized clinical forms, which can occur on the same horse simultaneously and can transform between types — particularly toward more aggressive forms when disturbed or incompletely treated:

    1. Occult (Flat) Sarcoid

    Circular or irregular areas of gray, scaly, hairless skin. Often found around the eyes, face, and neck. Frequently mistaken for ringworm or rub marks. The least aggressive type at presentation but capable of transforming into verrucous or nodular types, especially after trauma or inappropriate treatment.

    2. Verrucous (Wart-like) Sarcoid

    Raised, rough, cauliflower-like surface resembling a wart or thick callus. Common on lower limbs, belly, groin, and axilla. Can extend deeper into the dermis than they appear.

    3. Nodular Sarcoid

    Firm, well-defined nodules under the skin. Type A has normal overlying skin; Type B has thinned skin adherent to the nodule (common in groin and sheath). Type B has higher risk of aggressive transformation and ulceration.

    4. Fibroblastic Sarcoid

    Aggressive, fleshy, ulcerated masses. Often resembles proud flesh or fungating tumor. Common on lower limbs after trauma or as a consequence of incomplete treatment. High recurrence rate. Can invade deeper structures over time.

    5. Mixed Sarcoid

    A lesion showing features of two or more types at the same site — for example, a verrucous periphery with a fibroblastic center. Mixed types indicate active transformation and are generally more aggressive.

    6. Malevolent (Infiltrating) Sarcoid

    The most aggressive type. A network of sarcoid tissue that infiltrates along lymphatic vessels and fascial planes, often visible as a cord of thickened skin running away from the primary lesion. Most common on the face, medial thigh, and axilla. Locally destructive; requires specialist referral.

    Common Locations

    • Around the eyes (periocular): dangerous due to proximity to the globe
    • Ear base, lips, muzzle
    • Axilla and groin: thin skin, friction, difficult treatment access
    • Sheath and prepuce: very common; fly attraction complicates management
    • Lower limbs: especially at wound sites, fetlock, and pastern
    • Belly and chest

    Diagnosis

    Experienced veterinarians often diagnose sarcoids on clinical appearance alone. One critical rule:

    Never biopsy a suspected sarcoid without a treatment plan in place. Biopsy can trigger aggressive transformation — a quiescent occult sarcoid can become fibroblastic or malevolent within weeks of being cut. The exception is when diagnosis is genuinely uncertain and treatment will follow immediately. Discuss this with your vet before any biopsy.

    Other tools: PCR testing for BPV DNA in atypical presentations. Key differentials: ringworm (dermatophytosis), habronemiasis (summer sores), proud flesh (exuberant granulation tissue), papillomas, melanoma (especially grey horses), squamous cell carcinoma.

    Treatment Options

    There is no single universally effective treatment. Recurrence rates vary widely between treatments and individual horses. Location, size, type, and number of lesions determine which approach is appropriate.

    Do not attempt to treat sarcoids with home remedies (toothpaste, bloodroot paste, caustic household chemicals). These lack evidence, often cause local tissue damage without eliminating tumor cells, and can trigger aggressive transformation.

    Cisplatin (Intralesional Chemotherapy)

    Cisplatin oil-in-water emulsion or beads injected directly into the tumor at 2-week intervals. Best for accessible, clearly defined lesions under approximately 4 cm. Reported success rates 65–90% for periocular sarcoids (Theon et al., Equine Vet J, 1999). Requires handling of a cytotoxic agent — veterinary administration only. Not suitable for large, diffuse, or malevolent lesions.

    Liverpool White Cream (AW4-LUDES)

    A topical heavy-metal combination (including arsenic trioxide), available through veterinary channels. Applied at 5-day intervals over a prescribed cycle. Causes controlled necrosis of treated tissue. Effective for flat, verrucous, and some nodular sarcoids. Regulatory availability varies by country. Reported success rates approximately 50–75%. Requires veterinary oversight — damage to surrounding tissue is possible with imprecise application.

    Cryotherapy (Liquid Nitrogen)

    Liquid nitrogen spray or probes freeze the tumor; multiple freeze-thaw cycles per treatment, typically 2–3 sessions needed. Well-suited for small, flat periocular and some verrucous lesions. Not effective for deep or large tumors. Treated tissue sloughs slowly. Success rates variable (40–80%); recurrence common if deep margin is not reached.

    Surgical Excision

    Wide excision has recurrence rates of 50–60% for most sarcoid types — sarcoid tissue infiltrates beyond the visible margin, and the surgical wound stimulates recurrence. Most appropriate when combined with another modality (radiation, chemotherapy) or for pedunculated fibroblastic sarcoids with accessible bases. Avoid excision alone for most types.

    Radiation (Brachytherapy)

    Radioactive implants (iridium-192 or gold-198) placed into tumor tissue. Most commonly used for periocular sarcoids where surgical margins are limited. Reported cure rates of 75–90% in periocular cases (Knottenbelt et al.). Requires specialist facilities and radiation safety protocols. Not widely available; significant cost.

    Immunotherapy (BCG Vaccine)

    BCG (Bacillus Calmette-Guerin) injected intralesionally stimulates immune response against the tumor. Best results for periocular sarcoids (66% complete response in some series). Multiple injections at 2–4 week intervals. Allergic reactions possible; epinephrine should be available. Available through veterinary practitioners.

    Topical Imiquimod (Aldara 5% cream)

    Imiquimod is a toll-like receptor agonist that stimulates local immune responses. Applied topically 3 times weekly to occult or verrucous sarcoids for weeks to months. Evidence is modest but positive in some case series; best suited for flat periocular lesions where other treatments carry high risk of ocular damage. Available by veterinary prescription. Requires owner commitment to regular application.

    Watch and Wait (Active Monitoring)

    For small, stable, non-irritated occult or verrucous sarcoids in locations that are not causing welfare problems, some veterinarians recommend monitoring without treatment, particularly in areas where treatment-induced transformation is a significant risk. This requires regular (at least 3-monthly) reassessment. Not appropriate for rapidly enlarging or irritated lesions.

    The Golden Rules of Sarcoid Management

    1. Get a proper diagnosis first. Not every raised skin lesion is a sarcoid; wrong diagnosis leads to wrong treatment
    2. Consult a vet with equine dermatology experience. General recommendations fail regularly on sarcoids; referral to an equine dermatologist or oncologist is appropriate for complex cases
    3. Never traumatize a sarcoid without a treatment plan. No scratching, rubbing with equipment, ill-fitting tack, or biopsy without immediate follow-up treatment
    4. Match treatment to type and location. There is no universal protocol
    5. Plan for follow-up. Even “successful” treatments require monitoring for recurrence
    6. Protect wound sites. Fly control around existing lesions and wounds reduces re-inoculation risk

    Prognosis

    • Single, stable occult lesion: good prognosis for long-term stability with monitoring
    • Verrucous or nodular in accessible locations: good prognosis with appropriate treatment
    • Periocular sarcoids: guarded — treatment carries ocular risk; specialist care strongly recommended
    • Fibroblastic on lower limbs: guarded — high recurrence risk; may require multiple treatment modalities
    • Malevolent/infiltrating: poor for resolution; management aims at slowing progression and maintaining welfare

    When to Involve Your Vet Immediately

    • Any lesion near the eye — do not delay; periocular sarcoids are the most functionally threatening
    • Rapid change in size or character of any skin lesion
    • Lesion bleeding, ulcerating, or attracting excessive fly activity
    • Multiple new lesions appearing simultaneously
    • Any lesion in the groin, axilla, or sheath that is enlarging

    This article is for educational purposes only. Sarcoid management should be guided by a veterinarian with experience in equine dermatology. It does not constitute veterinary advice.

    For other skin conditions, see our articles on Rain Rot, Sweet Itch, and Hair Loss in Horses. For coat-color genetics and conditions that can be confused with coat-pattern variation, the equine coat genetics resource at Brindle Horses covers the hereditary brindle pattern in depth. Quick equine health reference at horse-info.org.

  • Tying Up in Horses: Causes, Emergency Response, and Prevention (ER, PSSM, RER)

    Tying up — the common term for exertional rhabdomyolysis (ER) — is a painful, sometimes dangerous condition where a horse’s muscles break down during or shortly after exercise. The horse becomes suddenly distressed, reluctant to move, and in severe cases cannot walk at all. It can look like colic from the outside, but the pain is in the muscles, not the gut. Knowing how to recognize it and what to do in the first minutes can make a significant difference in outcome.

    What Is Tying Up?

    Exertional rhabdomyolysis is the breakdown (lysis) of skeletal muscle tissue during or after exercise. When muscle fibers break down, they release myoglobin (the oxygen-carrying protein in muscle) into the bloodstream. Myoglobin is filtered through the kidneys, turning urine dark brown or red — a hallmark sign called myoglobinuria. In severe cases, the myoglobin load can damage the kidneys (acute renal failure), making prompt fluid therapy critical.

    Tying up ranges from mild (post-exercise muscle soreness and stiffness that resolves with rest and anti-inflammatories) to life-threatening (complete inability to move, severe muscle swelling, kidney failure).

    Signs and Symptoms

    An episode typically begins during or immediately after exercise — often within minutes of stopping. Classic signs:

    • Sudden reluctance or inability to move — the horse plants its feet and refuses to go forward
    • Hard, cramped, painful hindquarter muscles — the gluteals and epaxial muscles (back) are often rock-hard and tender to the touch
    • Sweating — disproportionate to the exercise intensity
    • Rapid breathing and elevated heart rate
    • Pain signs: pawing, looking at flanks (can mimic colic), anxious expression
    • Dark urine — brown or coffee-colored urine is a serious sign of myoglobinuria; call the vet urgently
    • Muscle trembling or shaking
    • In severe cases: recumbency (horse goes down and cannot rise)

    Types of Tying Up: Sporadic vs. Chronic/Recurrent

    Two broad categories have different causes, management strategies, and prognoses:

    Sporadic (Exertional) Rhabdomyolysis

    Occurs in otherwise healthy horses as a one-off event, usually triggered by identifiable causes:

    • Exercise beyond conditioning level: asking a horse to work harder or longer than its fitness level allows
    • High-grain diet with reduced exercise (“Monday morning disease”): rest days with full grain rations cause glycogen accumulation; return to work triggers ER. Classic in working horses rested over a weekend on full feed
    • Electrolyte imbalances: severe deficiencies in sodium, potassium, calcium, or magnesium impair muscle function
    • Vitamin E and selenium deficiency: these antioxidants protect muscle membranes; deficiency increases ER susceptibility. Selenium-deficient soils are common in many regions
    • Concurrent illness or fever: respiratory infection + exercise is a documented trigger
    • Heat and humidity: exercise in high heat/humidity stress increases ER risk, especially with inadequate electrolyte replacement

    Chronic (Recurrent) Exertional Rhabdomyolysis

    Horses that tie up repeatedly despite appropriate management have an underlying muscle disorder. Two well-characterized genetic conditions:

    Polysaccharide Storage Myopathy (PSSM / EPSM)

    PSSM (also called EPSM — Equine Polysaccharide Storage Myopathy) is a genetic disorder of glycogen metabolism. The muscle accumulates abnormal polysaccharide, leading to ER with even modest exercise, and often also to muscle atrophy and poor topline. Two types:

    • PSSM Type 1: caused by a mutation in the GYS1 gene (glycogen synthase); affects draft breeds, warmbloods, Quarter Horses, and many related breeds. Highly prevalent: 36% of draft horses in some studies (McCue et al., J Vet Intern Med, 2008). Diagnosed by genetic test (hair or blood) or muscle biopsy with PAS staining showing abnormal polysaccharide accumulation
    • PSSM Type 2: muscle biopsy shows abnormal glycogen without the GYS1 mutation; genetic basis less well characterized. Diagnosed by biopsy only

    Management of PSSM: low-starch, high-fat diet (dramatically reduce grain/starch; replace with fat such as rice bran, vegetable oil, or fat-supplemented feeds); daily turnout and regular exercise — consistent daily movement is as important as diet. Many PSSM horses become comfortable and workable with diet + management changes alone.

    Recurrent Exertional Rhabdomyolysis (RER)

    RER is primarily a disorder of intracellular calcium regulation in muscle, causing irregular muscle contractions. Predominantly affects Thoroughbreds, Standardbreds, and Arabian breeds. Mares are more commonly affected than geldings. Triggers include exercise intensity, excitement, and dietary starch. Confirmed by muscle biopsy (shows normal glycogen; distinguishes from PSSM). Management: controlled exercise routine; reduce starch in diet; in mares with cycle-linked episodes, progesterone supplementation or dantrolene sodium (a calcium channel stabilizer) before exercise may help. Work with a veterinary internist for recurrent cases.

    Emergency: What to Do During an Episode

    If your horse ties up during exercise:

    1. Stop immediately. Do not walk the horse forward to “walk it out” — this is the opposite of what’s needed. Forced movement with muscle breakdown actively increases muscle damage and myoglobin release
    2. Keep the horse still and calm. Stand with the horse, keep it quiet
    3. Call the vet. Any episode involving dark urine, recumbency, or severe distress is a veterinary emergency. Mild episodes warrant a same-day call; anything severe warrants an immediate call
    4. Keep the horse warm. Apply blankets to the hindquarters in cold weather — cold worsens muscle cramping. Do not hose with cold water
    5. Do not administer NSAIDs (bute, banamine) without veterinary guidance. NSAIDs are sometimes used for pain, but in severe rhabdomyolysis with myoglobinuria they can worsen renal damage by reducing renal blood flow. Your vet will decide this
    6. Do not feed grain. Water is fine if the horse will drink
    7. Transport carefully if needed: if the vet recommends transport to a clinic, do so in a well-bedded trailer; minimize further muscle stress

    Veterinary Treatment

    The vet’s priorities are:

    • Blood work: CK (creatine kinase) and AST (aspartate aminotransferase) are the key muscle enzymes; peak CK >50,000 IU/L indicates severe rhabdomyolysis. BUN and creatinine assess kidney function
    • Urinalysis: confirm myoglobinuria
    • IV fluids: the primary treatment for moderate-to-severe ER. High fluid volumes flush myoglobin through the kidneys before it causes tubular damage
    • Pain management: butorphanol or flunixin at low doses if the horse is in severe pain; conservative dosing to protect kidneys
    • Muscle relaxants: acepromazine (a phenothiazine) is sometimes used — it reduces anxiety and has mild vasodilatory effects that may improve muscle circulation; use is controlled
    • Selenium/vitamin E supplementation if deficiency is suspected
    • Electrolyte correction: IV electrolytes as needed

    Diagnosis of the Underlying Cause

    After stabilization, workup for recurrent cases includes:

    • Genetic testing for GYS1 mutation (PSSM Type 1) — done from mane hair or blood; widely available through veterinary and commercial labs
    • Muscle biopsy — the definitive diagnostic for PSSM Type 2, RER, and other myopathies; taken from the semimembranosus or gluteus medius under sedation
    • Selenium and vitamin E serum levels
    • Diet history: starch and sugar content of current ration
    • Thyroid panel: hypothyroidism is a rare contributor

    Prevention

    For Sporadic ER (no underlying condition)

    • Reduce grain on rest days: cut concentrate rations by at least half on non-work days; eliminate them entirely on unexpected days off
    • Regular conditioning: fit horses tied up far less often; build fitness gradually and maintain it consistently
    • Electrolyte supplementation: provide electrolytes in feed or water year-round for horses in regular work; increase during heat, competition, or heavy sweating
    • Vitamin E and selenium: have blood levels checked; supplement if deficient (selenium supplementation must be precise — toxicity is possible; do not exceed safe ranges without testing)
    • Adequate warm-up: proper walk/trot warm-up before demanding work, especially in cold weather

    For PSSM

    • Low-starch, high-fat diet (target <10% non-structural carbohydrates in total diet)
    • Daily turnout — no long stall rest periods
    • Gradual return to exercise after any rest period
    • Avoid alfalfa (higher in sugar than grass hay for some horses); test hay NSC if possible

    For RER

    • Consistent daily exercise routine — irregular schedules worsen RER
    • Reduce grain/starch; replace calories with fat
    • Reduce pre-exercise excitement; quiet, calm handling
    • Dantrolene sodium (given orally 1–1.5 hours before exercise) may reduce ER episodes in confirmed RER horses — veterinary prescription

    When to Call the Vet

    • Immediately: horse is recumbent (down and unable to rise), has dark brown/red urine, or is in severe distress
    • Same day: any episode of muscle cramping/stiffness after exercise, even if mild
    • Scheduled visit: horse has tied up more than once; needs workup for underlying myopathy

    Tying up is a genuine emergency when severe. Do not delay calling your veterinarian. This article is for educational purposes and does not constitute veterinary advice.

    For guidance on recognizing signs of pain that owners often miss, see Signs of Pain That Owners Miss. For information on metabolic conditions related to muscle health, see our coverage of Equine Metabolic Syndrome. Quick equine health definitions at horse-info.org.

  • Horse Deworming Guide: Internal Parasites, Resistance, and Targeted Selective Treatment

    Internal parasites are a reality of horse ownership, but how we manage them has changed fundamentally in the last two decades. Blanket rotational deworming — giving the same drug to every horse on a fixed schedule — is now understood to actively drive anthelmintic resistance. The modern standard is targeted selective treatment (TST): test first, treat only horses with significant worm burdens, rotate drugs based on resistance data, and monitor effectiveness. This guide explains what parasites your horse faces, how to identify them, and how to build a rational deworming program.

    The Major Internal Parasites of Horses

    Large Strongyles (Strongylus vulgaris, S. edentatus, S. equinus)

    Once the most dangerous equine parasite, large strongyles were the leading cause of fatal verminous arteritis. Larvae of S. vulgaris migrate through the cranial mesenteric artery wall, causing thromboembolism and colic. The near-eradication of large strongyles in managed horses is one of the genuine success stories of modern deworming — but that success has masked a new threat from small strongyles.

    Small Strongyles (Cyathostomins) — the Current Primary Threat

    Over 40 species of small strongyles (cyathostomins) infect horses. Unlike large strongyles, they do not migrate through arterial walls — but they have a dangerous survival trick: hypobiosis. Larvae can arrest their development inside the intestinal mucosa for months to years, emerging en masse in late winter or early spring. Mass emergence causes larval cyathostominosis: acute or subacute protein-losing enteropathy with severe diarrhea, weight loss, ventral edema, and a high mortality rate in untreated horses.

    Small strongyles are also the primary driver of anthelmintic resistance. Resistance to benzimidazoles (fenbendazole, oxibendazole) is near-universal in many populations. Resistance to pyrantel is widespread. Macrocyclic lactone (ivermectin, moxidectin) resistance is emerging and confirmed in multiple countries.

    Roundworms (Parascaris equorum)

    Roundworms primarily affect foals and young horses (under 18 months). Heavy ascarid burdens cause respiratory signs during the lung migration phase (coughing, nasal discharge — “summer colds”), then intestinal impaction, colic, and pot-bellied appearance. Critically: Parascaris resistance to ivermectin and moxidectin is now widespread globally (Reinemeyer & Nielsen, Equine Vet J, 2009). Fenbendazole and pyrantel currently retain better efficacy against roundworms — this is a reversal from the historical pattern and affects foal deworming protocols.

    Pinworms (Oxyuris equi)

    Pinworms cause intense perianal itching. The female deposits eggs around the anus, leaving a yellowish egg mass. The main sign is tail rubbing — horses rub their tail heads raw against fences, posts, and stall walls. Pinworms are not detected on routine fecal egg counts because the eggs are deposited externally, not shed in feces. Diagnosis: a piece of clear tape pressed around the anus and examined under a microscope (the “tape test”). Treatment: standard anthelmintics plus meticulous cleaning of the perianal area to remove egg masses before they cycle back to infective larvae.

    Tapeworms (Anoplocephala perfoliata)

    Anoplocephala perfoliata aggregates at the ileocecal junction, where heavy burdens cause ulceration, spasmodic colic, and ileocecal intussusception. Transmitted via oribatid mites (pasture forage mites). Standard fecal egg counts do NOT detect tapeworm eggs reliably. Detection options:

    • Tapeworm saliva ELISA (Equisal test): a salivary antibody test with good sensitivity for moderate-to-heavy burdens; available directly or through your vet
    • Serum ELISA: blood test; high sensitivity
    • Modified McMaster with a flotation solution of high specific gravity: can detect eggs but low sensitivity

    Treatment: double-dose pyrantel (13.2 mg/kg) or praziquantel (licensed in combined products, e.g., Quest Plus, Equimax). Once or twice yearly; autumn treatment before oribatid mite activity peaks is commonly recommended.

    Bot Flies (Gasterophilus spp.)

    Bot flies lay yellow eggs on the horse’s legs (and occasionally face/mane/tail) in late summer and autumn. The horse licks the eggs; larvae hatch, migrate through the mouth, then attach to the stomach lining where they develop over winter, passing out in spring manure. Heavy burdens cause gastric ulceration and irritation. Most ivermectin products cover bots; moxidectin does not have a label claim for bots in all jurisdictions. Autumn/winter treatment after the first killing frost (once the fly season ends) eliminates the current year’s larvae.

    Lungworms (Dictyocaulus arnfieldi)

    Horses are aberrant hosts — they rarely carry patent lungworm infections, but donkeys and mules are efficient reservoir hosts. Horses kept with donkeys can develop chronic cough from larval migration. Suspect lungworm in any coughing horse kept with donkeys where other causes have been excluded. Ivermectin is effective.

    Anthelmintic Drug Classes

    Drug classExamplesPrimary targetsResistance status
    BenzimidazolesFenbendazole (Panacur), OxibendazoleSmall strongyles, roundworms, some large strongylesWidespread resistance in cyathostomins; Parascaris less affected
    PyrimidinesPyrantel (Strongid)Large and small strongyles, roundworms, tapeworms (double dose)Widespread resistance in cyathostomins in some regions
    Macrocyclic lactonesIvermectin (Eqvalan), Moxidectin (Quest)Small + large strongyles, bots (ivermectin), roundworms (NB: resistance)Emerging resistance in cyathostomins; Parascaris resistance widespread
    Praziquantel (combination only)Quest Plus, EquimaxTapewormsNo resistance documented to date

    The Problem With Rotational Deworming

    Rotational deworming — cycling through all available drug classes on a calendar schedule — was designed to prevent resistance by not giving one drug continuously. Paradoxically, it achieved the opposite: by treating ALL horses frequently, it maximized selection pressure on parasites across all drug classes simultaneously.

    The key insight from population biology: a small percentage of parasites (the “refugia”) that never contact anthelmintics dilute resistant genes back into the population. Treating low-shedding horses contributes nothing to parasite control but eliminates refugia and amplifies selection for resistance. The goal of modern deworming is to preserve refugia while treating horses with genuine burdens.

    Targeted Selective Treatment (TST): The Modern Standard

    TST is endorsed by the American Association of Equine Practitioners (AAEP) and the European Scientific Counsel Companion Animal Parasites (ESCCAP). The core principle: use fecal egg count (FEC) to identify high-shedding horses, treat them, and leave low-shedding horses untreated.

    Step 1: Fecal Egg Count (FEC)

    A fecal egg count (eggs per gram, EPG) measures the strongyle egg output from a fresh manure sample using the McMaster technique. Horse population studies consistently show a highly skewed distribution: roughly 80% of parasite eggs are shed by 20% of horses. The shedding categories:

    • Low shedders: <200 EPG — treat once or twice yearly; no more
    • Moderate shedders: 200–500 EPG — treat 2–3 times yearly
    • High shedders: >500 EPG — treat 3–4 times yearly, monitor closely

    Individual horses tend to maintain their shedding category over time — a horse that’s a low shedder this year will likely be a low shedder next year. Confirm category annually or biannually.

    Step 2: Fecal Egg Count Reduction Test (FECRT)

    The FECRT tells you whether a deworming drug is actually working in your herd. Protocol: FEC before treatment, repeat 14 days after benzimidazole or pyrantel treatment (10–14 days is the window for these drugs); 21 days after ivermectin; 21 days after moxidectin. Calculate percent reduction:

    (Pre-treatment EPG — Post-treatment EPG) / Pre-treatment EPG x 100 = % reduction

    • >95% reduction: good efficacy
    • 90–95%: suspected resistance
    • <90%: confirmed resistance — do not use this drug class in your herd

    Run a FECRT when you set up a new program, whenever you switch drug classes, and if clinical signs suggest deworming is failing. This is the only way to know if what you’re giving is working.

    Step 3: Seasonal Timing and Strategic Treatments

    Even in TST programs, some strategic timed treatments target lifecycle events:

    • Autumn (post-frost): moxidectin targets the hypobiotic encysted cyathostomin larvae in the gut wall — the only drug with meaningful efficacy against the arrested L3 stage. Use once yearly in autumn for horses in high-strongyle environments
    • Autumn/winter: praziquantel for tapeworms
    • Autumn (after fly season): ivermectin for bot larvae
    • Spring (for high shedders): clear the peak spring buildup before grass re-growth amplifies pasture contamination

    Special Populations

    • Foals and weanlings: highest roundworm burden; treat with fenbendazole or pyrantel at 2–3 months, then FEC-guided from 6 months. Do NOT use ivermectin or moxidectin as the primary foal dewormer given widespread Parascaris resistance
    • Yearlings: still at roundworm risk; transition to strongyle-focused TST by 18–24 months
    • New arrivals: treat on arrival (moxidectin or ivermectin + praziquantel), quarantine 48 hours before pasture contact, FEC to establish baseline
    • Pregnant mares: treat around foaling with a safe drug (ivermectin is considered safe; moxidectin has a stronger caution in pregnant mares — consult your vet); reduces environmental contamination for the foal
    • Donkeys: higher lungworm burden; treat more frequently; separate from horses or treat the herd simultaneously

    Signs Your Horse May Have a Heavy Parasite Burden

    • Rough, dull coat despite good nutrition
    • Weight loss or failure to thrive despite adequate feed
    • Pot-bellied appearance (especially in young horses)
    • Recurrent mild colic
    • Diarrhea, loose manure, or poor manure consistency
    • Tail rubbing (pinworms)
    • Coughing in young horses (roundworm lung migration)
    • Bot fly eggs visible on the legs in late summer/autumn

    None of these signs are specific to parasites — many other conditions cause them. A fecal egg count + veterinary evaluation is the appropriate response, not a precautionary deworming that may not address the actual cause.

    Pasture Management to Reduce Parasite Burden

    Drug treatment alone cannot solve a pasture contamination problem. Environmental management reduces the infectious larval population on pasture:

    • Remove manure twice weekly: larvae develop from eggs within 2–3 days in warm conditions; regular pickup before infective L3 develop dramatically reduces pasture contamination
    • Harrowing: spreading manure piles exposes larvae to desiccation in dry/sunny weather; counterproductive in wet, mild conditions (spreads infective larvae)
    • Cross-grazing with cattle or sheep: equine strongyles do not infect ruminants and vice versa; cattle/sheep consume equine larvae without becoming infected, reducing pasture larval load
    • Pasture spelling: resting pastures for 4–6 months significantly reduces larval survival, especially in dry climates
    • Avoid overstocking: high horse density per acre concentrates contamination; larger paddocks + lower density = lower per-horse larval challenge
    • Compost manure properly: heap composting generates heat that kills strongyle larvae; do not spread fresh horse manure directly onto horse pastures

    Larval Cyathostominosis: The Emergency You Must Know

    Larval cyathostominosis is a medical emergency. It occurs when large numbers of inhibited small strongyle larvae simultaneously emerge from the gut wall, typically in late winter or early spring. The result is acute protein-losing enteropathy:

    • Acute onset profuse watery diarrhea
    • Rapid, severe weight loss and protein loss
    • Ventral edema (bottle jaw, leg edema)
    • Fever in some cases
    • High mortality rate without aggressive treatment

    At-risk horses: those with previous periods of heavy exposure (newly rescued horses, horses from poorly managed properties) or horses whose anthelmintic treatment has failed. Treatment: moxidectin (the only drug with significant efficacy against the inhibited larvae) plus supportive care (IV fluids, plasma, nutrition support). Mortality can exceed 50% in severe cases — call your vet immediately if you see sudden diarrhea + weight loss + edema in a horse with an unknown or spotty deworming history.

    Building Your Property’s Deworming Program

    1. Establish a baseline FEC for every horse on the property (including new arrivals)
    2. Run a FECRT to confirm efficacy of the drug you plan to use
    3. Categorize shedders (low/moderate/high) and treat accordingly
    4. Set strategic timed treatments: autumn moxidectin (encysted larvae), autumn/winter tapeworm (praziquantel), post-frost bot (ivermectin)
    5. Re-run FEC annually to confirm categories and track herd trends
    6. Work with your vet: resistance patterns vary regionally; your vet will know local resistance prevalence and can interpret FECRT results

    When to Call the Vet

    • Any horse with acute diarrhea + weight loss + edema — emergency, possible larval cyathostominosis
    • FEC results consistently high despite deworming — suspect resistance, run FECRT
    • Foal with colic and suspected roundworm impaction
    • Any horse with colic after deworming — parasite die-off can rarely cause impaction
    • Designing a new TST program for a multi-horse property

    This article is for educational purposes only and does not constitute veterinary advice. Deworming programs should be designed with your veterinarian based on your specific herd, region, and resistance data.

    For guidance on vital signs to monitor in an unwell horse, see our How to Check Vital Signs guide. For quick reference definitions of equine health terms, the equine health glossary at horse-info.org is a useful companion.

  • Navicular Disease in Horses: Causes, Symptoms, and Management

    Navicular disease is one of the most common causes of chronic front-leg lameness in horses, affecting performance horses, warmbloods, and stock breeds in disproportionate numbers. Despite its name, the condition is rarely limited to a single small bone — modern imaging has revealed it involves an entire anatomical region at the back of the foot, which is why veterinarians increasingly prefer the term palmar foot pain or caudal heel syndrome.

    If your horse is showing subtle, intermittent front-leg lameness that worsens on hard ground or in circles, navicular disease belongs on your differential list. The good news: with an accurate diagnosis and targeted management, many horses remain comfortable and useable for years.

    What Is Navicular Disease?

    The navicular apparatus sits deep in the horse’s hoof, wedged between the coffin bone and the short pastern bone. It consists of:

    • The navicular bone (distal sesamoid bone) — a small, shuttle-shaped bone
    • The deep digital flexor tendon (DDFT) — which wraps under and around the navicular bone
    • The navicular bursa — a fluid-filled sac that cushions the tendon–bone interface
    • Supporting ligaments — the collateral sesamoidean ligaments and the impar ligament

    Pain can originate from any of these structures — bone degeneration, tendon damage, bursitis, or ligament deterioration — or from several simultaneously. MRI has shown that pure “navicular bone disease” is actually the minority presentation; most cases involve DDFT pathology at the fibrocartilage interface. This is why “navicular syndrome” or “palmar foot pain” is more accurate than the classical name.

    Which Horses Are at Risk?

    Navicular syndrome is predominantly a disease of:

    • Warmbloods and sport horses used in jumping and dressage
    • Stock breeds (Quarter Horses, Paint Horses) — particularly those with a genetic tendency toward upright pasterns and small, contracted feet
    • Thoroughbreds in race or event training
    • Horses with small, steep-heeled, or contracted hooves
    • Horses with long toe / low heel conformation

    Ponies and horses with wide, well-proportioned hooves are affected much less frequently. The condition almost always affects the front feet; bilateral front lameness is common and can be subtle enough that owners mistake it for a “lazy” or “stiff” horse.

    Causes and Contributing Factors

    No single cause explains navicular syndrome across all horses. Contributing factors include:

    • Conformation: upright pasterns increase concussion; long toe / low heel increases DDFT tension at the navicular bone; contracted heels narrow blood supply
    • Work on hard surfaces: repetitive concussive loading accelerates bone remodeling and fibrocartilagous damage
    • Poor circulation: the navicular bone’s vascular supply is already limited; vascular changes are seen on radiograph as “lollipop” or “flask” shaped synovial invaginations (“synovial fossae”)
    • Genetics: selective breeding for small feet in Quarter Horses; conformational traits are heritable
    • Farriery history: chronic underrun heels, broken-back hoof-pastern axis, long-toe shoeing all increase DDFT load

    Signs and Symptoms

    Navicular syndrome is notorious for its subtle, progressive onset. Early signs owners commonly describe:

    • Intermittent, low-grade front-leg lameness — worse after rest, improving slightly with light exercise (“warms out of it”)
    • Reluctance to work on hard ground or circles; preference for soft footing
    • Toe-pointing when standing — the horse shifts weight off the heel by resting on the toe of the affected foot
    • Stumbling or tripping more frequently than usual
    • Shortened stride, choppy gait — especially at trot
    • Bilateral front lameness that looks like “stiffness” rather than a clear single-leg limp

    As the condition progresses:

    • Lameness becomes more consistent and more pronounced
    • Hoof shape may change — contracted heels, upright boxy foot (the horse adapts gait to protect the heel)
    • Positive “wedge test” or palmar foot flexion (nerve block eliminates lameness in the palmar digital nerve region)

    The Toe-Pointing Test

    When your horse stands and rests one front leg on its toe rather than the heel, this “toe-pointing” is a classic early-warning sign of palmar foot pain. It shifts load away from the painful heel region. A horse that toe-points regularly and warms out of the stiffness deserves a prompt veterinary lameness evaluation.

    Diagnosis

    Accurate diagnosis requires a veterinary lameness evaluation. Steps typically include:

    1. Visual assessment at rest and in motion — gait quality, hoof conformation, toe-pointing
    2. Hoof testers — pressure applied across the frog and heel; positive in many (not all) navicular cases
    3. Flexion tests — palmar foot and distal limb flexion; positive flexion response suggests caudal foot involvement
    4. Nerve blocks (perineural anesthesia) — the diagnostic gold standard. Palmar digital (PD) nerve block at the heel eliminates or significantly improves the lameness, confirming caudal heel pain. A navicular bursa block (intrasynovial) is definitive for bursal involvement.
    5. Radiographs (X-rays) — assess bone shape, synovial fossae (invaginations), cortical thinning, calcifications. Radiograph alone cannot diagnose DDFT or bursal pathology.
    6. MRI or CT — the definitive imaging modality, especially for soft-tissue (DDFT, impar ligament, collateral ligaments) involvement. Low-field standing MRI is now widely available at referral clinics. Reveals pathology invisible on X-ray.
    7. Ultrasound — useful for assessing the pastern region of the DDFT proximal to the hoof; less useful deep inside the hoof capsule.

    A horse with bilateral front lameness may appear nearly sound on a straight line because both sides compensate for each other. Lunging on a circle and performing serial nerve blocks are key to unmasking bilateral disease.

    Treatment and Management Options

    There is no cure for structural navicular pathology, but most horses are manageable — often for many years — with a combination of farriery, medication, and workload modification. Treatment depends on which structures are affected and the degree of degeneration.

    1. Corrective Farriery (the cornerstone)

    Farriery modification is the single most impactful long-term intervention. Goals:

    • Restore correct hoof-pastern axis: broken-back axis (long toe / low heel) dramatically increases DDFT tension at the navicular bone; correcting it reduces pain
    • Egg-bar or heart-bar shoes: extend heel support, encourage frog loading, improve weight distribution
    • Rolled or rocker toe: reduces breakover effort, lessening DDFT tension during push-off
    • Wedge pads: elevating the heel (typically 2–6 degrees) reduces DDFT tension; used short-term to establish comfort while corrective farriery re-establishes heel growth
    • Shoeing cycle regularity: 6–week maximum cycle; long-between-shoeing intervals worsen heel collapse

    Work with a vet-farrier team. Corrective work done without diagnostic clarity can worsen the condition.

    2. Medication

    • Isoxsuprine hydrochloride: a vasodilator historically prescribed to improve navicular bone blood supply. Evidence base is modest; commonly used as an adjunct
    • NSAIDs (phenylbutazone / flunixin): short-term pain management; not a long-term solution due to gastrointestinal and renal risks with chronic use
    • Intra-bursal corticosteroids: injection of corticosteroid (typically triamcinolone or methylprednisolone) into the navicular bursa provides significant medium-term relief (typically 3–6 months); often combined with hyaluronic acid
    • Coffin joint injection: the distal interphalangeal joint communicates with the navicular bursa in about 25–30% of horses; coffin joint injection can provide relief when the bursa is the primary pain source
    • Bisphosphonates (tiludronate / clodronate): bone resorption inhibitors licensed in horses (Tildren, Osphos) for navicular bone degeneration. Studies (Denoix et al., 2011, JAVMA) show measurable improvement in lameness scores. Administered IV or IM; require veterinary prescription; repeat every 6–12 months
    • Platelet-rich plasma (PRP) / stem cells: emerging biologics for DDFT pathology at the navicular fibrocartilage interface; evidence is building but not yet definitive

    3. Neurectomy (palmar digital neurectomy)

    When conservative management fails, palmar digital neurectomy — surgical sectioning of the palmar digital nerves — eliminates sensation in the heel region. The horse may return to work, often soundly. Important caveats:

    • Underlying pathology continues to progress; the horse simply no longer feels it
    • Serious risk: catastrophic DDFT rupture — without pain feedback, the horse may work beyond the tendon’s structural limit. Enhanced monitoring is essential.
    • Neuroma formation can cause return of pain; repeat neurectomy may be needed
    • Competition rules vary: many disciplines prohibit neurectomized horses

    Neurectomy is a tool of last resort when quality of life (comfort at pasture, breeding use) is the goal and athletic use is no longer the priority. Discuss honestly with your vet before choosing this path.

    4. Exercise and Surface Management

    • Consistent, moderate exercise on soft, level surfaces maintains circulation and tendon health better than stall rest
    • Avoid prolonged hard-surface work and tight circles on compromised footing
    • Turnout on level pasture (not rocky or uneven ground) is generally beneficial
    • Regular light exercise prevents the wasting-from-disuse cycle that worsens long-term prognosis

    Prognosis

    Prognosis depends on which structures are affected and how early intervention begins:

    • Bone changes only, mild: good prognosis for years of managed work with farriery + occasional injections
    • DDFT core lesion at the navicular fibrocartilage: guarded; may require repeated injections and workload reduction to maintain comfort
    • DDFT tear / severe impar ligament pathology: poor for athletic function; pasture soundness with farriery and pain management may be achievable

    The most important prognostic factor is quality of the diagnostic workup. Horses managed empirically without imaging often receive the wrong farriery, the wrong injection site, or no injection at all. Get MRI if you can — it changes the treatment plan in a significant proportion of cases.

    Prevention and Hoof Health

    • Buy conformation carefully: avoid horses with small contracted feet, steep pasterns, or significant broken-back hoof-pastern axis
    • Regular, consistent farriery on a 5–6 week schedule; never let heels collapse between visits
    • Footing management: minimize prolonged work on asphalt, concrete, or rock-hard arena surfaces
    • Weight management: obesity increases concussive loading on the foot
    • Early veterinary evaluation of any intermittent, subtle front-leg lameness — early intervention before structural change yields far better outcomes

    When to Call the Vet

    • Any front-leg lameness that persists beyond 2–3 days
    • Bilateral front stiffness or choppy trot that does not resolve with light warm-up
    • Toe-pointing at rest, especially if recurring
    • Sudden worsening in a horse with known navicular history
    • Any lameness in a horse post-neurectomy — this is urgent (possible DDFT rupture)

    This article is for educational purposes. It is not veterinary advice. Always consult your veterinarian for any lameness evaluation or treatment decision.

    For a broader overview of hoof and leg conditions in horses, see our Hoof & Leg Problems category. For quick definitions of equine health terms, the equine health reference at horse-info.org provides at-a-glance glossary entries and condition summaries.

  • EHV-1 Quarantine and Biosecurity Guide for Stables and Barns

    Equine herpesvirus-1 (EHV-1) is a highly contagious respiratory pathogen that can spread rapidly through barns and stables, causing fever, nasal discharge, cough, and in severe cases, neurological complications or abortion in pregnant mares. Once EHV-1 enters a facility, it can affect multiple horses in days without proper quarantine and biosecurity measures. While equine herpesvirus is endemic in horse populations worldwide, the difference between a minor isolated case and a facility-wide outbreak often comes down to swift, decisive action and solid quarantine protocols. This guide outlines the practical steps horse owners and barn managers should take to contain EHV-1 exposure, protect herd health, and work effectively with your veterinary team.

    Quarantine and biosecurity are not just emergency responses; they are foundational practices that should be part of your stable’s standard operating procedures long before an EHV-1 case appears. Whether you board at a public facility, manage a private farm, or operate a breeding operation, understanding the timing, staffing, and logistical requirements of quarantine will help you respond calmly and effectively if your herd faces exposure. This article is informational and does not replace veterinary diagnosis or treatment; always consult your equine veterinarian for specific medical guidance and when you suspect EHV-1 in your horses.

    Understanding EHV-1 Transmission and Risk

    EHV-1 spreads primarily through respiratory secretions: nasal discharge, saliva, and aerosolized particles from coughing or sneezing. An infected horse can shed virus for 7-10 days during the acute phase of illness, and some horses may shed intermittently for weeks. The virus is also shed in feces, urine, and reproductive fluids (placental tissue in aborted fetuses), making it a multi-route threat in barns with shared water sources, feed, equipment, and tack.

    Contaminated hands, clothing, grooming tools, saddles, bridles, and vehicle tires are common vectors. A single handler moving between an infected horse and a healthy horse without hand hygiene can transmit the virus. Environmental surfaces (stall railings, doorknobs, wash racks) remain infectious for hours in cool, moist conditions and can retain virus for days on hay and feed. This environmental persistence is why biosecurity extends beyond the sick horse to the entire facility.

    Immediate Steps When EHV-1 is Suspected or Confirmed

    Call Your Veterinarian Right Away

    If you notice signs of EHV-1 in one or more horses—fever (102.5°F or higher), nasal discharge, cough, depression, or in emergency cases, hind limb weakness or ataxia—contact your equine veterinarian immediately. A confirmed diagnosis through nasopharyngeal swab, PCR testing, or serology guides the scope and duration of quarantine. Your vet will also assess whether any horses show neurological signs (EHV-1 myeloencephalopathy, or EHM), which requires intensive supportive care and may necessitate emergency hospitalization.

    If a horse on your property shows sudden hind limb paralysis, inability to urinate, or severe loss of coordination, call your veterinarian or emergency clinic immediately. These signs suggest EHV-1 with neurological involvement, a medical emergency requiring rapid intervention.

    Isolate Affected Horses Immediately

    As soon as EHV-1 is suspected, move the affected horse or horses to a separate, well-ventilated stall or paddock away from other horses. Ideally, this is a separate barn building or a completely isolated area with at least 15 feet of distance between the quarantined horse and others. If your barn layout does not permit physical separation, use solid barriers (not open rails) and maximize ventilation.

    Assign dedicated staff to care for the quarantined horse. If that is impossible, ensure handlers care for the quarantined horse last in the daily routine, after all other horses, and change clothes and footwear before exiting the isolation area. Assign dedicated water buckets, feed containers, grooming tools, and equipment to the quarantined horse; do not move these items between horses.

    Quarantine Duration and Monitoring

    The standard quarantine period for a horse with confirmed EHV-1 respiratory disease is a minimum of 2-3 weeks after the horse shows clinical recovery (normal appetite, temperature, and activity level). A horse that becomes febrile (fever above 102.5°F) must reset the 2-week clock from its last fever. Some veterinarians recommend 3-4 weeks of quarantine for extra safety, particularly on farms with multiple horses or in breeding operations.

    For horses exposed to EHV-1 but not yet showing symptoms, implement quarantine protocols for 14-21 days while monitoring closely for fever, nasal discharge, or cough. Take rectal temperatures twice daily (morning and evening) during the high-risk exposure period. Any fever during this window suggests active infection and extends the quarantine timeline.

    Biosecurity Protocols for the Quarantine Zone

    Stall and Environmental Management

    • Clean and disinfect the isolation stall thoroughly before placing a suspected EHV-1 horse inside. Remove old bedding, sweep, and use an approved equine disinfectant (phenolic compounds, quaternary ammonium, or iodine-based products) on all surfaces, railings, water troughs, and feed containers.
    • Provide fresh bedding daily and remove soiled bedding in a designated waste area, away from other horse facilities. If possible, compost soiled bedding separately from the main manure pile for 4-6 weeks, as EHV-1 virus can survive in manure under cool, moist conditions.
    • Maintain strict hand hygiene: wash hands thoroughly with soap and warm water or use alcohol-based sanitizer before entering and immediately after leaving the quarantine area. Gloves offer an additional layer of protection but must be changed between tasks.
    • Use dedicated feed and water buckets. Wash and disinfect these items daily if reusing them after the quarantine period ends. If possible, use disposable feed containers during quarantine to eliminate cross-contamination risk.
    • Minimize visitor contact with the quarantined horse and surrounding area. If visitors must enter, provide clean coveralls, gloves, and dedicated footwear or boot covers. No sharing of personal items, hats, or equipment.

    Clothing, Footwear, and Equipment Management

    Staff and handlers should change clothes and footwear before leaving the quarantine area. Contaminated clothing can shed virus onto other areas of the barn or farm. Dedicated boots or boot covers should stay in the quarantine zone. If someone must move between the quarantined horse and other horses, changing outer clothing is essential. Wash contaminated clothing in hot water and machine dry.

    Disinfect any tack, grooming tools, or equipment that contacted the quarantined horse by soaking in a disinfectant solution (per product instructions) or storing isolated from other equipment for the duration of quarantine. Do not share saddles, bridles, halters, lead ropes, or grooming kits with non-quarantined horses during this period.

    Respiratory Hygiene and Coughing Containment

    When handling a horse with suspected EHV-1, be aware of respiratory particle spread. If the horse coughs, step back and allow the air to clear. Avoid working directly upwind of the quarantined horse’s face, as respiratory secretions travel several feet on air currents. Turn the horse’s head away from other barn areas and outdoor paddocks when possible. Wear a mask yourself if you have any respiratory symptoms, as cross-species transmission is rare but the principle of not introducing additional pathogens to a sick horse is sound.

    Facility-Wide Biosecurity During Quarantine

    Feed and Water Management

    Use separate water sources for quarantined horses and the rest of the herd. If a shared water system is unavoidable, clean and disinfect the system (water troughs, hoses, troughs) daily. EHV-1 can survive in water for a limited time; frequent turnover and disinfection reduce this risk. Feed separate hay and grain to the quarantined horse; do not pull from the main hay supply or grain storage if there is any risk of cross-contamination.

    Clean feed storage areas and grain bins regularly. Do not allow contaminated hands or equipment to contact feed meant for non-quarantined horses.

    Movement and Exposure Precautions

    During quarantine, restrict movement of the affected horse(s) to the designated isolation area. Do not move the quarantined horse to shared paddocks, wash racks, or arenas. If the horse requires veterinary procedures that must take place in communal areas, disinfect those areas afterward or schedule its appointments last in the day.

    Limit entry to the quarantine zone. Establish a sign at the entrance (e.g., “EHV-1 Quarantine – No Entry Without Permission”) to alert visitors and barn staff. This simple visual cue prevents inadvertent contact and reminds handlers of the infection risk.

    Vehicle and Visitor Management

    If a horse is trailered during or after quarantine, disinfect the trailer thoroughly before using it for other horses. Wash the interior, floor, and windows with approved disinfectant; allow to air dry. Boots, wheels, and exterior surfaces can also carry contaminated material.

    If you transport hay, equipment, or other materials from a facility with confirmed EHV-1, allow these items to be exposed to sunlight and air for 24-48 hours before bringing them onto your property, if possible. UV light and ventilation reduce the infectious viral load on environmental surfaces.

    Restrict visitor access to the property during active quarantine. If vendors, farriers, or veterinarians must visit other horses, they should visit the non-quarantined horses first and the quarantined area last. Provide clean gloves, boot covers, and a disinfectant station at the quarantine entrance.

    Testing and Clearance from Quarantine

    Before releasing a horse from quarantine, confirm clinical recovery: normal appetite and attitude, normal rectal temperature (98.5-100.5°F) for at least 7-14 consecutive days, and resolution of respiratory signs. Some veterinarians recommend a final nasopharyngeal swab for PCR to confirm the horse is no longer shedding virus, particularly if the horse will return to a high-traffic facility or breeding operation.

    Horses recovering from EHV-1 respiratory disease typically develop protective immunity, but re-infection can occur if exposed to a new strain or after several years. Vaccination with inactivated EHV-1 vaccine (given as a series before exposure) or modified live vaccines (in certain populations) offers some protection. Discuss vaccination strategy with your veterinarian to protect your herd long-term.

    Special Considerations for Breeding Operations and High-Risk Facilities

    Breeding barns, racing facilities, and boarding operations face heightened EHV-1 risk due to frequent horse movement and new arrivals. Implement these additional measures:

    • New arrival quarantine: Quarantine new horses for 10-14 days before introducing them to the main herd. Collect nasopharyngeal swabs on arrival and again at day 7 if purchasing from an unknown source or an area with known EHV-1 activity.
    • Vaccination protocols: Maintain up-to-date EHV-1 vaccination records for all resident horses. While vaccines do not prevent infection completely, they reduce severity and duration of shedding.
    • Pregnancy monitoring: If a pregnant mare is exposed to EHV-1, monitor her closely for signs of abortion (loss of pregnancy with no prior warning or full labor). EHV-1 can cause abortion weeks after respiratory symptoms resolve. Pregnant mares exposed to EHV-1 should be segregated from non-pregnant horses for the quarantine period, as aborted fetal material is highly infectious.
    • Staff training: Ensure all barn staff understand EHV-1 transmission routes and biosecurity procedures. Regular training and written protocols (posted in the barn) reinforce compliance.
    • Logbook and health records: Document the date of suspected or confirmed EHV-1 exposure, affected horses, quarantine start and end dates, and any additional horses showing clinical signs. This record is essential for your veterinarian and for future reference.

    Disinfectants and Environmental Sanitation

    EHV-1 is susceptible to many common disinfectants. Approved options for barns include the following, used per product label instructions:

    Disinfectant Type Effective Against EHV-1 Typical Use
    Phenolic compounds (e.g., Lysol-type disinfectants) Yes Stall surfaces, railings, water troughs, equipment
    Quaternary ammonium (e.g., Virkon-S diluted) Yes General barn disinfection, non-corrosive
    Iodine-based disinfectants (e.g., Betadine solution) Yes Hand hygiene, equipment soaking, wound management
    Sodium hypochlorite (bleach, 1:10 dilution) Yes Hard surfaces, concrete, rubber mats (use with caution on materials)
    Alcohols (70% ethanol or isopropyl) Yes Hand sanitizer, small equipment, tack (test on sensitive surfaces)

    Always follow label directions for dilution, contact time, and safety. Some disinfectants can corrode certain materials or harm surfaces, so test on inconspicuous areas first. For maximum effectiveness, clean visible organic material (manure, hay, bedding) before disinfecting, as dirt and debris can reduce disinfectant efficacy.

    Frequently Asked Questions

    How long does EHV-1 survive on surfaces outside the horse?

    EHV-1 is an enveloped virus, making it relatively fragile compared to non-enveloped viruses. It survives for hours on hard surfaces at room temperature, longer in cool and moist environments (shaded, damp stalls). Sunlight, dry conditions, and heat reduce survival time to minutes to hours. On hay and feed, the virus may persist for 24-48 hours under cool, humid conditions. This is why daily disinfection and frequent bedding changes are key components of quarantine.

    Can humans catch EHV-1 from horses?

    No. EHV-1 is species-specific and does not infect humans. Humans cannot become ill from handling an infected horse or their respiratory secretions. However, humans can act as mechanical vectors, carrying the virus on hands, clothing, and equipment from an infected horse to a susceptible horse. Proper hand hygiene and clothing changes are therefore critical to protect other horses, not yourself.

    My boarding facility had an EHV-1 case last month. Can I bring my horse there now?

    This depends on the facility’s response and timeline. If the quarantine was properly implemented, the affected horse(s) are cleared by a veterinarian, and the facility has undergone thorough disinfection, the risk is low. Ask the facility manager for documentation of the quarantine period, disinfection date, and a veterinary clearance statement. If the case occurred fewer than 2-3 weeks ago, ask about any additional horses that developed signs. Request a written biosecurity and quarantine protocol for future events before moving your horse.

    Should my horse be vaccinated against EHV-1?

    Talk with your equine veterinarian about vaccination. EHV-1 vaccines are available and recommended for horses at moderate to high risk: breeding mares, young horses, horses at boarding facilities, or horses in regions with recent EHV-1 activity. Vaccines reduce the severity and duration of clinical disease and shedding, though they do not guarantee absolute protection. Pregnant mares may have additional vaccination considerations; discuss these with your vet. Horses previously infected with EHV-1 typically have some natural immunity but are not immune to re-infection.

    What if a horse develops neurological signs during quarantine?

    If a horse shows hind limb weakness, ataxia (stumbling or incoordination), inability to rise, or loss of tail tone during or shortly after EHV-1 respiratory illness, this suggests EHV-1 myeloencephalopathy (EHM), a serious neurological form of the disease. Call your veterinarian or emergency clinic immediately. EHM requires intensive supportive care, anti-inflammatory medications, and possibly hospitalization. The horse must remain in strict quarantine due to continued viral shedding. Some horses recover fully with aggressive treatment, while others may have permanent neurological deficits. Early intervention offers the best chance of recovery.

    Key Takeaways

    • EHV-1 spreads through respiratory secretions and contaminated surfaces; quarantine and biosecurity are essential to prevent facility-wide outbreaks.
    • Immediately isolate any horse showing fever, nasal discharge, or cough; contact your equine veterinarian for diagnosis and guidance.
    • Quarantine duration is a minimum of 2-3 weeks after clinical recovery, with temperature monitoring twice daily for the first 14-21 days of exposure.
    • Assign dedicated staff, equipment, and supplies to the quarantined horse; disinfect stalls, buckets, and tools daily; and prevent cross-contamination through strict hand and footwear hygiene.
    • Inform visitors, farriers, and other service providers of the quarantine; disinfect vehicles and shared equipment that contact the quarantined horse.
    • For pregnant mares exposed to EHV-1, monitor closely for late-term abortion; aborted tissue is highly infectious and requires special handling and disinfection.
    • After quarantine clearance, disinfect the entire facility and consider vaccination of the herd to reduce the risk of future EHV-1 outbreaks.
    • Keep detailed records of the exposure, affected horses, quarantine dates, and veterinary recommendations for future reference and herd health planning.
    • This article provides general guidance and is not a substitute for veterinary diagnosis or treatment; always consult your equine veterinarian for specific medical advice and emergency situations.

    References


    Related

  • EHV-1 Symptoms: Early Warning Signs and When to Call the Vet

    Equine herpesvirus-1 (EHV-1) is a highly contagious respiratory virus that affects horses of all ages and can progress rapidly from mild symptoms to serious complications. Many horse owners miss the earliest warning signs of EHV-1 infection because the initial symptoms appear subtle and may resemble other common equine illnesses. Understanding the earliest indicators of EHV-1 infection–before your horse develops obvious clinical disease–is critical to stopping viral spread, supporting recovery, and preventing severe neurological complications that can develop within days of infection onset.

    The key to protecting your horse and your barn lies in recognizing the very first signs of illness. EHV-1 often begins with fever and behavior changes that many owners attribute to stress, weather changes, or minor illness. This article focuses specifically on the early warning signs that should trigger immediate veterinary attention, the biphasic fever pattern characteristic of EHV-1, and how to distinguish these subtle symptoms from normal variations in your horse’s daily health.

    Understanding EHV-1 Infection Timeline

    EHV-1 spreads through respiratory secretions, direct contact, and fomites (contaminated equipment, clothing, and surfaces). After exposure, the incubation period typically ranges from 2 to 10 days before the first symptoms appear. During this window, your horse may be shedding virus and exposing other horses in your barn without showing any signs of illness. Once symptoms begin, they can escalate quickly, making early detection essential.

    The infection progresses through distinct phases. The respiratory phase begins with fever and mild upper respiratory signs. If your horse’s immune system controls the virus at this stage, recovery may proceed smoothly. However, if viral replication continues unchecked, the virus can spread to the central nervous system, potentially causing neurological disease that ranges from subtle incoordination to complete paralysis.

    The Biphasic Fever: Your First Real Clue

    One of the most distinctive and earliest signs of EHV-1 infection is a biphasic fever pattern–meaning your horse’s temperature rises, may drop briefly, and then rises again. This pattern is not typical of many other equine illnesses and should immediately raise suspicion for EHV-1.

    How to Recognize Biphasic Fever

    • First fever spike: Temperature rises to 101.5-104.0 F (38.6-40.0 C), typically lasting 24 to 48 hours
    • Apparent recovery period: Temperature drops, sometimes appearing nearly normal for 12 to 24 hours, causing owners to believe the horse is recovering
    • Second fever spike: Temperature rises again, often to the same range or higher, accompanied by worsening respiratory or neurological signs

    Many horse owners take a single temperature reading when a horse seems unwell, find it elevated, and then assume recovery is underway if the next day’s temperature is lower. This false sense of security during the apparent recovery period is dangerous. Vigilant owners should measure temperature every 4 to 6 hours during any unexplained fever to detect the biphasic pattern early. If you observe two distinct fever spikes separated by a brief interval of normal or near-normal temperature, contact your veterinarian immediately and suspect EHV-1 until proven otherwise.

    Subtle Behavioral Changes Before Fever Appears

    Fever is not always the first sign. Some horses show behavioral and attitude changes before their temperature becomes elevated. These early signs are easy to overlook because they mimic stress, fatigue, or minor discomfort from many causes.

    Pre-Fever Behavioral Indicators

    • Lethargy and depression: Your horse appears unusually quiet, stands for extended periods with head low, and shows diminished interest in food or the environment
    • Appetite changes: Reduced interest in hay or grain, or slower eating pace than normal
    • Increased eyelid drooping (ptosis): Eyes appear partly closed without obvious irritation or injury
    • Inattention: Your horse seems withdrawn, unresponsive to sounds or activities that normally catch their attention
    • Reluctance to exercise: Decreased energy during turnout or riding, unusual stumbling or clumsiness
    • Hollow appearance: Loss of belly definition over just 24 to 48 hours as the horse eats less and stops drinking normally

    If your horse displays any combination of these signs–especially if they develop acutely (suddenly, within hours) rather than gradually over days–measure their temperature immediately. Even if temperature is normal, document the signs and call your veterinarian. EHV-1 can cause subtle neurological signs before fever becomes obvious, and early intervention may prevent progression to severe disease.

    Early Respiratory Signs

    While EHV-1 is classified as a respiratory virus, the earliest respiratory signs are often extremely mild and easy to dismiss. Owners frequently expect obvious nasal discharge or coughing, but EHV-1 may begin with signs so subtle that they seem insignificant.

    Mild Respiratory Indicators to Watch

    • Slight nasal discharge: Clear or slightly cloudy discharge from one or both nostrils; may appear only when you lead your horse around, not at rest
    • Quiet cough: Occasional, sporadic cough that sounds dry or slightly productive; fewer than 5 to 10 coughs per day in early infection
    • Mild congestion sounds: Subtle increased respiratory noise during exercise; may disappear at rest
    • Reluctance to eat hay: Difficulty chewing hay due to throat soreness; your horse may drop hay or chew slowly without obvious coughing

    The absence of heavy nasal discharge or frequent coughing does not rule out EHV-1. Many horses are infected and highly contagious before developing obvious respiratory signs, or they may never develop coughing at all. If your horse shows even mild respiratory signs along with fever or behavior changes, isolate the horse and contact your veterinarian.

    Early Neurological Signs: A Critical Red Flag

    Neurological signs can appear very early in EHV-1 infection, sometimes before–or instead of–obvious respiratory illness. These subtle signs are often misinterpreted as minor injuries, poor footing, or rider error. Recognizing them early is essential because neurological damage progresses rapidly once it begins.

    Subtle Neurological Warning Signs

    • Incoordination (ataxia) in the hind limbs: Swaying or wavering from side to side when standing still, particularly noticeable when viewed from behind; loss of precise hind-limb placement when walking
    • Shortened stride: Your horse’s gait becomes choppy or restricted without obvious lameness or pain
    • Stumbling or tripping: More frequent trips or stumbles than normal, especially on uneven ground or when turning sharply
    • Dragging toes: Particularly the hind toes; you may see scuff marks on shoes or hooves
    • Difficulty backing: Hesitation or unsteadiness when asked to back up; loss of precise hind-limb control
    • Facial nerve involvement: Drooping of one side of the face, difficulty eating or drinking, drooling
    • Urinary dysfunction: Inability to retract penis in stallions, dribbling urine, or fecal incontinence

    Neurological signs demand immediate emergency veterinary evaluation. If your horse shows any incoordination, difficulty moving, or facial nerve changes, call your veterinarian immediately. Do not wait 24 hours to see if the sign resolves on its own. Neurological EHV-1 progresses rapidly, and early intervention with specific therapies (such as high-dose acyclovir or valacyclovir) may prevent permanent damage.

    Environmental and Herd Factors That Increase Risk

    Understanding when your horse is at heightened risk for EHV-1 exposure helps you implement heightened vigilance. Certain situations create ideal conditions for viral transmission and rapid spread within a barn population.

    Risk Factor Why It Matters Your Action
    Recent horse show or event participation Exposure to horses from multiple facilities and regions; incubation period is 2-10 days post-exposure Isolate returning horses for 14 days; monitor temperature and signs daily
    New horse arrival at the barn Quarantine period may be insufficient if the horse is in early incubation phase Separate new arrivals for at least 4 weeks; use dedicated staff and equipment
    Shared water troughs or equipment Virus survives on surfaces and spreads via contaminated equipment and fomites Disinfect shared items daily during any suspected illness; separate water sources
    Overcrowded turnout or housing Close proximity increases respiratory transmission risk Increase space between horses if any show signs of illness
    Mixed age groups without separation Young horses and immunocompromised individuals are more vulnerable Monitor younger and older horses more closely; isolate high-risk animals first

    If any horse at your facility has been exposed to horses from other locations, or if you are attending multiple barns, implement strict hygiene protocols immediately: wash hands and change clothes between facilities, disinfect equipment, and monitor your horse closely for 14 days following potential exposure.

    Taking Your Horse’s Temperature Accurately

    Accurate temperature measurement is your best tool for early EHV-1 detection. Normal equine body temperature ranges from 98.0 to 101.0 F (36.7 to 38.3 C), with average being 99.5 F (37.5 C). Any sustained reading above 101.5 F (38.6 C) warrants investigation.

    • Use a digital thermometer (rectal measurement is most reliable)
    • Insert thermometer 2 to 3 inches into the rectum at a slight upward angle
    • Hold in place for 30 to 60 seconds until the thermometer beeps
    • Measure temperature at the same time each day for consistency
    • During any illness, measure temperature every 4 to 6 hours to detect fever patterns
    • Document readings in writing or on your phone so you can describe the pattern to your veterinarian

    If you observe an unexplained fever above 102.0 F (38.9 C) lasting more than 12 hours, do not wait. Contact your veterinarian and describe any other signs you have noticed. Provide your temperature measurements and the timeline of symptom onset. This information is critical to rapid diagnosis and early treatment initiation.

    When to Call Your Veterinarian Immediately (Emergency Situations)

    Some situations require emergency veterinary attention, not routine appointment scheduling:

    • Fever above 103.5 F (39.7 C) lasting more than 12 hours
    • Any neurological signs: incoordination, difficulty walking, facial drooping, or dragging toes
    • Biphasic fever pattern (fever dropping then rising again within 24 to 48 hours)
    • Inability or severe reluctance to stand or move
    • Sudden onset of severe lethargy or depression with high fever
    • Difficulty swallowing, excessive drooling, or inability to drink
    • Paralysis of any limb or part of the body
    • Any sign of urinary incontinence or inability to urinate

    Your veterinarian can perform nasopharyngeal or tracheal swabs for PCR testing (polymerase chain reaction), blood tests, and neurological examination to confirm EHV-1 infection and assess severity. Early diagnosis allows for prompt initiation of antiviral therapy, supportive care, and strict isolation protocols to prevent spread to other horses in your facility.

    Isolation Protocols If EHV-1 Is Suspected

    If your horse shows signs suspicious for EHV-1, isolation is not optional–it is essential to protect other horses in your barn. The virus is highly contagious and spreads rapidly through respiratory secretions and contaminated equipment.

    • Physically separate the suspected horse from all other horses immediately
    • Assign dedicated staff and equipment (halter, lead, grooming supplies, water bucket) to the isolated horse
    • Wear protective clothing (coveralls, gloves, boot covers) when handling the horse and change before approaching other horses
    • Disinfect all equipment and surfaces with a dilute bleach solution (1 part bleach to 10 parts water) or quaternary ammonium disinfectant daily
    • Do not share hay feeders, water troughs, or grooming supplies between the isolated horse and others
    • Maintain isolation for at least 14 to 21 days after the last fever, and longer if neurological signs are present
    • Consult your veterinarian on the appropriate duration of isolation based on your horse’s clinical course and test results

    Frequently Asked Questions

    Can EHV-1 kill a horse?

    Yes, EHV-1 can be fatal, though death rates vary. Most horses with respiratory EHV-1 infection recover with appropriate supportive care. However, horses that develop severe neurological disease (particularly paralysis) have a much poorer prognosis. Some affected horses must be euthanized due to severe, irreversible neurological damage. Pregnant mares infected with EHV-1 may abort (lose pregnancy). Early recognition and treatment significantly improve outcomes, which is why early detection is so critical.

    How is EHV-1 diagnosed?

    Your veterinarian will diagnose EHV-1 using PCR testing on samples collected via nasopharyngeal or tracheal swabs, or blood tests. PCR is the most sensitive and specific test, particularly when collected during the first week of infection. Antibody testing (serology) may show evidence of prior infection but does not diagnose active, current infection. Your veterinarian will combine test results with clinical signs to confirm diagnosis.

    Can vaccinated horses get EHV-1?

    Yes, vaccinated horses can become infected with EHV-1. Vaccines reduce the risk and severity of infection, but do not provide complete protection. Vaccinated horses that become infected typically have milder disease and shorter recovery times. However, they can still shed virus and infect other horses. If you have vaccinated horses that show signs of illness, follow the same isolation and diagnostic protocols as unvaccinated horses.

    How long does it take to recover from EHV-1?

    Recovery from respiratory EHV-1 typically takes 2 to 6 weeks with appropriate care. However, neurological disease recovery is much slower and often incomplete. Horses with neurological EHV-1 may require weeks to months of supportive care and rehabilitation, and some never fully recover normal coordination. The severity of initial infection and speed of treatment initiation significantly impact recovery timeline and outcome.

    Should I vaccinate my horse against EHV-1?

    The decision to vaccinate should be made in consultation with your veterinarian based on your horse’s age, use (competition horses are higher risk), and exposure risk in your region or facility. Vaccines are available as respiratory vaccines (given intramuscularly or intranasally) and pregnant mare vaccines (to prevent abortion). Your veterinarian can recommend the best vaccination protocol for your horse. Even vaccinated horses require the same vigilant monitoring for early signs, as vaccination does not guarantee protection.

    Key Takeaways

    • EHV-1 infection often begins with subtle signs: lethargy, slight fever, mild nasal discharge, or behavior changes that mimic minor illness or stress
    • The characteristic biphasic fever pattern–fever that drops then rises again within 24 to 48 hours–is a strong indicator of EHV-1 and demands immediate veterinary evaluation
    • Neurological signs (incoordination, stumbling, facial drooping, difficulty backing) can appear early and progress rapidly; any neurological sign requires emergency veterinary attention
    • Monitor your horse’s temperature daily during any illness or after potential exposure to infectious horses; document patterns and report them to your veterinarian
    • Isolate any horse with suspected EHV-1 immediately to prevent spread to other horses in your barn
    • Contact your veterinarian promptly if you observe unexplained fever lasting more than 12 hours, behavior changes, neurological signs, or respiratory illness
    • Early recognition and veterinary intervention significantly improve prognosis and reduce the risk of severe neurological complications and death
    • This article is not a substitute for veterinary diagnosis or treatment; always consult your equine veterinarian regarding your horse’s health and medical care

    References


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