Blog

Paralysis is the complete or partial loss of voluntary motor function in one or more muscle groups, resulting from disruption at any level of the motor pathway from the cerebral cortex through the spinal cord to the peripheral nerve and neuromuscular junction. In horses, paralysis is classified by anatomical distribution: monoplegia (one limb), hemiplegia (one side), paraplegia (both hindlimbs), and tetraplegia or quadriplegia (all four limbs). Common equine causes include equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona, equine herpesvirus type 1 (EHV-1) myeloencephalopathy, cervical vertebral stenotic myelopathy (Wobbler syndrome), botulism affecting the neuromuscular junction, and peripheral nerve damage following trauma or injection site injury. Laryngeal hemiplegia, the partial paralysis of the left arytenoid cartilage caused by damage to the left recurrent laryngeal nerve, is among the most common neurological conditions in performance horses and produces the characteristic inspiratory noise known as roaring. Facial nerve paralysis can result from ill-fitting halters or head trauma. Diagnosis of the underlying cause requires neurological examination, cerebrospinal fluid analysis, serology, and imaging. Treatment depends on etiology; supportive care, physical therapy, and specific antiprotozoal treatment for EPM may be indicated. See also EHV-1 myeloencephalopathy, a viral cause of spinal cord damage and ataxia, and sudden collapse from sleep dysfunction for a non-paralytic differential with overlapping presentation.

Further Reading

• paralysis (Wikipedia)
• For clinical causes and management of equine limb paralysis: leg paralysis in horses: MSD Veterinary Manual

Narcolepsy is a neurological sleep disorder characterized by recurrent episodes of uncontrollable drowsiness and sudden loss of muscle tone (cataplexy) that precipitate collapse into sleep. In horses, narcolepsy is rare and can be idiopathic or secondary to underlying conditions such as liver disease, equine protozoal myeloencephalitis, or hypersomnia associated with sleep deprivation from an inability to achieve recumbent rest. Affected horses exhibit characteristic behavior: they become progressively drowsy, the head drops, the knees buckle, and the horse may collapse partially or fully before partially awakening. Skin abrasions on the knees, fetlocks, and muzzle from repeated partial falls are a common physical finding. Diagnosis requires ruling out other causes of episodic weakness or collapse, including paralysis, hypoglycemia, and cardiac arrhythmia. The orexin (hypocretin) system implicated in human and canine narcolepsy is also relevant in horses; imipramine has been used diagnostically and therapeutically. Environmental assessment is important because horses that cannot lie down comfortably in their stabling may develop secondary sleep deprivation that mimics narcolepsy. See also motor pathway disruption as the primary differential when distinguishing true paralytic episodes from narcoleptic collapse, and fetlock anatomy for understanding the abrasion pattern that accumulates from repeated partial falls.

Further Reading

• narcolepsy (Wikipedia)
• For differential diagnosis of sleep-related and neurologic behavior issues: behavior problems in horses: MSD Veterinary Manual

Equine infectious anemia (EIA) is a retroviral disease caused by a lentivirus in the family Retroviridae, closely related to HIV in its mechanism of persistence. The virus infects macrophages and monocytes, integrates permanently into the host genome, and is never cleared, an infected horse carries EIA for life. The disease is sometimes called swamp fever or horse malaria, names that reflect historical descriptions of the intermittent fever that marks acute episodes.

Transmission occurs primarily via blood transfer: large biting insects (horse flies and deer flies of the family Tabanidae) mechanically carry virus on mouthparts interrupted mid-meal and moved to another horse. Contaminated needles and surgical instruments are the principal iatrogenic route, a particular concern in historical herd vaccination programs where needles were reused. Vertical transmission from mare to foal across the placenta or in milk occurs at low frequency. EIA is not transmitted by casual contact, shared water, or small insects such as mosquitoes.

Clinical presentation falls into three patterns. Acute EIA produces high fever (up to 41 degrees C), thrombocytopenia, dependent edema, and severe anemia within 30 days of infection; untreated acute cases can be fatal. Chronic EIA follows with recurring febrile episodes every few weeks to months, progressive weight loss, and deteriorating body condition. Inapparent carriers show no clinical signs but remain persistently viremic and are the primary reservoir for transmission in managed herds.

The Coggins test (agar gel immunodiffusion, AGID) detects antibodies against EIA p26 antigen and is the regulatory standard for diagnosis. A positive Coggins result is a reportable finding in all US states and most countries; regulations require either lifelong quarantine at least 200 yards from all other equids, euthanasia, or export under USDA permit. Negative Coggins tests are required for interstate transport, competition entry, and most boarding facilities. A current negative test is a standard document in any horse purchase. There is no vaccine and no cure; control is entirely through testing and movement restriction. See also pre-purchase documentation requirements for why a current negative Coggins test is a non-negotiable item in any sale, and body condition scoring for monitoring the progressive deterioration seen in chronic EIA carriers.

Further Reading: The virology, Coggins test protocol, and regulatory requirements for EIA are detailed on Wikipedia’s Equine infectious anemia entry. Utah State University Extension’s equine health program publishes a practical overview of testing requirements at USU Extension: Equine Infectious Anemia.

Equine herpesvirus (EHV) is a family of DNA viruses belonging to the Herpesviridae, with five characterized subtypes in horses. EHV-4 causes primarily respiratory illness, rhinopneumonitis, most severe in young horses and resembling moderate influenza. EHV-1 causes respiratory disease but is distinguished by its capacity to produce two additional and more serious syndromes: abortion in pregnant mares and equine herpesvirus myeloencephalopathy (EHM), a neurological form that can cause ataxia, paralysis, and death.

Both EHV-1 and EHV-4 establish lifelong latency in the trigeminal ganglia and lymphocytes after primary infection. A horse that has recovered from EHV illness carries latent virus indefinitely and may reactivate shedding under stress, weaning, competition, transport, or concurrent illness. This means herd immunity is never complete and outbreak control depends on biosecurity and stress management rather than elimination of the virus from exposed populations.

EHM outbreaks at competition venues have become a recognized event-management concern. Affected horses display progressive hindlimb ataxia, bladder dysfunction, and in severe cases quadriplegia within days of fever onset. Case fatality in neurological EHV-1 infections ranges from 20 to 40 percent in outbreak settings, making prompt quarantine and reporting to regulatory authorities essential. The index of suspicion should rise for any horse that develops fever and neurological signs within 14 days of attending a competition or event.

Vaccination for EHV-1 and EHV-4 is available and recommended in the core vaccination schedule for horses with any exposure to other horses. Current vaccines reduce respiratory shedding and provide partial protection against abortion but do not reliably prevent EHM. Biosecurity during transport: checking temperatures during travel, limiting nose-to-nose contact, is the primary mitigation for horses moving between facilities. See also the core vaccination schedule for EHV-1 and EHV-4 timing and the limitation of current vaccines against neurological disease, and the Equus genus entry for the host-specificity context that gives all five EHV subtypes their name.

Further Reading: The five EHV subtypes, their clinical syndromes, and the EHM neurological form are covered on Wikipedia’s Equine herpesvirus article. Utah State University Extension provides a practical guide to EHV biosecurity and outbreak management at USU Extension: Equine Herpesvirus.

Voiding is the physiological process by which the body expels accumulated waste material , urine from the urinary bladder or feces from the large intestine. In horses, normal urinary voiding occurs several times per day, producing large volumes of pale yellow to cloudy urine. The cloudiness is characteristic and normal in healthy horses, caused by calcium carbonate crystals; it should not be confused with the turbid urine that signals inflammatory or infectious processes.

Fecal voiding frequency depends on diet and gut motility. Horses on continuous hay or pasture access may produce manure every one to two hours; those on twice-daily feeding schedules show a more clustered pattern. Any significant change in the frequency, volume, consistency, or odor of fecal changes in fecal output is clinically meaningful. Failure to void feces for more than 12 hours, combined with signs of abdominal discomfort, constitutes a potential potential colic emergency emergency.

Abnormal voiding patterns can signal a range of conditions. Straining to urinate (dysuria) with small or absent urine production in a male horse may indicate a urethral obstruction or uroliths. A horse that postures repeatedly to urinate without producing urine should be treated as urgent. Increased urinary frequency combined with excessive water intake (polyuria-polydipsia) occurs in conditions such as pituitary pars intermedia dysfunction (Cushing’s disease) and renal tubular disease.

In the foal, meconium voiding in the first hours of life is a critical health milestone monitored by any attentive handler. In adults, voiding behavior during exercise , a horse urinating at the walk during warm-up , is normal, though interrupting competition for elimination is sometimes managed with pre-event procedures by trainers.

A variant is any form of an animal, trait, or characteristic that differs from the accepted norm or standard for its type. In equine usage the term is applied broadly: a coat color that does not fit the major recognized categories is a color variant; a horse whose measurements fall outside breed average is a size variant; a horse carrying an unusual genetic mutation that changes its observable phenotype is a genetic variant. The word is descriptive rather than evaluative , a variant is neither inherently inferior nor superior to the standard form.

Coat color genetics produces numerous documented variants. The dilute genes responsible for buckskin, dilute pigmentation gene, piebald, and skewbald patterns all represent variants from the base bay, chestnut, or black pigmentation. Some variants have been selected for by breeders until they became characteristic of specific breeds; the Appaloosa’s spotted coat is a variant that defines the breed. Others, such as the “frame overo” pattern associated with the lethal white syndrome mutation, carry health implications that require careful breeding management.

Structural variants in conformation , a horse with unusually upright upright conformation noted in surveys or abnormally low withers , are commonly noted in purchase examination reports. These variants influence a horse’s suitability for specific disciplines, its soundness prognosis, and sometimes its market value.

In diagnostic contexts, “variant” may describe a laboratory result or imaging finding that falls outside the reference range without constituting a confirmed pathological change , a usage that calls for further investigation before clinical action.

Stool, also called manure or feces, is the solid or semi-solid waste material remaining after the digestive tract has extracted water and nutrients from ingested feed. In healthy adult horses, stool appears as distinct, formed balls of roughly uniform size, olive to dark brown in color, and with a mild odor of fermented fiber. Consistency and frequency vary with diet: horses on fresh pasture produce softer, greener stool, while those on dry hay produce drier, firmer fecal balls.

Monitoring stool is one of the simplest daily health checks available to horse owners. Changes in output , reduced manure production, abnormally dry or hard balls, diarrhea, or foul-smelling loose stool , frequently precede or accompany colic episodes, intestinal impaction, or infectious enteritis. A horse that has not produced stool in more than 12 hours warrants immediate veterinary assessment, as impaction impaction risk when output stops carries serious risk if untreated.

Parasite management programs rely in part on fecal egg counts extracted from fresh stool samples; routine fecal testing is the evidence-based foundation for fecal egg count sampling and helps avoid the resistance problems associated with calendar-based anthelmintic rotation.

Stool in the foal carries diagnostic significance beyond that in adults: meconium (first stool) retained in a newborn foal signals a potentially life-threatening obstruction. Normal meconium passage within the first few hours of life is a key neonatal milestone.

A trocar is a surgical instrument consisting of a sharply pointed stylet enclosed within a hollow cannula. When the trocar is thrust through the body wall into a fluid- or gas-filled cavity, the stylet is withdrawn, leaving the cannula in place as a port through which the contents can drain or through which instruments can be introduced. In equine medicine, trocars are most commonly employed in emergencies involving cecal or large-colon gas accumulation during gas-distension colic.

Cecal trocarization is a field procedure performed when a horse has massive cecal tympany (gas distension) that has not responded to initial medical management and when transport to referral surgery is not immediately available. Under sedation and after surgical preparation of the right flank, a large-bore trocar is inserted through the body wall into the cecum to release the accumulated gas and reduce intraluminal pressure. The procedure carries risks of peritoneal contamination and local infection, but in extreme circumstances it may be the measure that keeps the horse alive until surgery is possible.

Trocars are also used in thoracocentesis (draining pleural effusions from the chest cavity), abdominocentesis (collecting peritoneal fluid for diagnostic analysis), and in laparoscopic procedures as ports for instrument access. The term derives from French “trois-quarts” (three-quarters), historically referring to the triangular cross-section of the cutting tip.

Proper trocar technique requires accurate anatomical knowledge of insertion sites and strict aseptic preparation to avoid introducing peritoneal contamination risk-producing contamination into sterile body cavities.

Toxicity is the capacity of a substance to cause injury, illness, or death in a living organism. In equine medicine the term is used both as a property of a substance (e.g., “the toxicity of red maple leaves”) and as a clinical description of a horse’s condition when a toxic dose has been absorbed. Dose is the critical variable: virtually any substance is harmful at a sufficiently high concentration, and many substances with known toxic potential , such as certain therapeutic dose versus toxic threshold-based medications , are therapeutically beneficial at controlled doses.

Plant toxicity represents the most common source of equine poisoning. Horses on unmanaged unmanaged grazing exposure may encounter red maple, black walnut shavings, yew, bracken fern, Sorghum spp., or various alkaloid-bearing plants. Toxicity thresholds vary: a horse consuming a handful of yew leaves can die within hours from cardiac arrest, while chronic low-level ingestion of pyrrolizidine alkaloids from plants such as ragwort causes cumulative hepatic toxicity that presents clinically only after significant liver damage has accumulated.

Mycotoxins , toxic metabolites of molds growing on hay, grain, or silage , represent a subtler but pervasive risk. Fumonisin, deoxynivalenol, and aflatoxin are among the mycotoxins documented to cause neurological, reproductive, or hepatic disease in horses consuming contaminated feed. Feed testing is the only reliable way to assess mycotoxin risk before symptoms appear.

Chemical toxicity from pesticides, herbicides, heavy metals, or improperly stored medications is less common but clinically significant. Any horse with unexplained acute neurological signs, hepatic disease, or sudden death should be evaluated for toxic exposure; consultation with the body condition history and a thorough review of diet and environment are essential first steps.

A vat, in the context of livestock and equine management, is a large container , typically built of concrete, steel, or heavy-gauge plastic , filled with a liquid solution into which animals are driven or guided for immersion. The practice of dipping animals in a vat is primarily used to control external parasites such as ticks, lice, mites, and mange organisms that colonize the skin and mane and tail of horses and other livestock.

Dip vats are more common in cattle management than in horse management in modern practice, though they were historically used for horses in regions with high tick burdens. The solution in the vat , which may contain organophosphates, pyrethroids, or amitraz depending on the target parasite and regulatory approval , must be maintained at the correct concentration and refreshed regularly, as dilution from wet animals and photodegradation reduce efficacy over time.

In equine facilities, smaller spray or plunge vats are occasionally used for treating therapeutic foot soaking conditions such as thrush, white line disease, or chronic chronic dermatitis at the heel dermatitis, where prolonged contact between the affected tissue and a therapeutic solution improves treatment penetration. These are typically short-duration foot-soaking vessels rather than full-body immersion units.

Operator safety when using dip vats is a practical concern: concentrated acaricide solutions require protective gloves, eye protection, and adequate ventilation. Disposal of spent dip solution is subject to environmental regulations governing organophosphate and pyrethroid compounds.