Over the last several years there have been numerous outbreaks of Equine Herpes Virus (EHM) myeloencephalopathy infections in horses. Many of the outbreaks originated at shows or events where numerous horses were stabled together for a few days.

The cause of the outbreaks is Equine Herpes Virus-1 (EHV-1). Usually the virus causes respiratory signs including fever, poor appetite, coughing, nasal discharge and lethargy. It can cause abortion and neonatal death. In rare circumstances the virus may produce neurologic signs known as myeloencephalopathy. Loss of bladder and anal tone, mild incoordination, stumbling, hindlimb paralysis, and recumbency are signs of equine myeloencephalopathy.

Transmission from one horse to another comes from direct contact (nose to nose) or by contact with infected discharges carried on boots, buckets, blankets, trailers, hands, aborted fetus etc. The incubation period (time from infection to exhibiting clinical signs) is 2-14 days. Most horses have been infected with the respiratory form before the age of 2 years. Previous infection does not protect the horse from reinfection later in life. Some horses have a carrier or latency state in which they test positive but have no clinical signs. Stress may cause a recrudescence of the disease or result in shedding of the virus.

The virus can be treated with anti-viral drugs, which will lessen the severity of clinical signs if caught in the very early course of the disease. However, treatment is usually supportive (bladder drainage, anti-inflammatory drugs, sling) until the horse recovers on it own. If the horse becomes recumbent, the prognosis is poor.

Although vaccination for EHV-1 does give some protection against the respiratory form, it does not protect against the neurologic form. Following some simple management practices while at home and away can help protect your horse from infection. New horses on the farm, or horses that are returning to the farm after co-mingling with other horses should be kept away from horses on the farm for 21 days.

While at a horse show and when returning take your horse’s temperature every day. Contact a veterinarian the first day your horse has a fever. If EHV-1 is suspected, a nasopharyngeal swab can be obtained and submitted for tests to determine of EHV-1 is to blame. Horses exposed to EHM will be quarantined for 21 days following clinical signs to prevent spread of the disease.

There are many names for “it”: azoturia, set fast, paralytic myoglobinuria, and chronic exertional rhabdomyolysis (ER), but most of us know “it” as tying up. It is a common muscle problem in horses with multiple causes. The most common syndromes include Polysaccharide Storage Myopathy (PSSM), Recurrent Exercise Rhabdomyolysis (RER), vitamin/mineral deficiency, electrolyte imbalance, exhaustive exercise, especially on hot, humid days.  Some horses can have chronic episodes starting at a young age when exercised lightly. Depending on the cause of tying up, keeping your horse well hydrated and fit for exercise can help reduce tying up episodes.

PSSM is a common cause of chronic tying up in Quarter Horses, Paints, Appaloosas, Warmbloods, and Draft Breeds, although other breeds may be affected. In PSSM, horses have a genetic defect in the muscle cells which results in excessive storage of sugar known as glycogen. Most horse owners have reported that horses with PSSM have exercise intolerance. A genetic test is available for some breeds of horses that require only a hair sample or blood test. However, other breeds may need to have a muscle biopsy performed to diagnose the disorder. The diet for these horses should consist of low starch/low sugar feeds with a high fat percent.. Any change in diet should be done gradually. These horses should also have daily exercise to prevent muscle stiffness and liberal access to turnout.

Recurrent Exercise Rhabdomyolysis (RER) is another cause for chronic tying up and occurs when there is an abnormality in the way muscle cells regulate intracellular calcium. This type of tying up is not due to the calcium in the horse’s diet, but is also believed to be a genetic defect in the muscle cell. RER episodes occur with exercise or excitement, so keeping the horse calm is one part of prevention. Getting the horse conditioned to the stimuli, providing controlled daily exercise, and the least amount of time in the stall possible are the best ways to prevent RER.  A proper diet for these horses can be difficult because most are in training; they need enough calories to maintain that level without making them high strung.  Fat is a good energy source without making them “hot”.  The most common breeds with RER are Arabians, Standardbreds, and Thoroughbreds.

Tying up episodes can range from mild to severe. A horse can present with a tucked-up abdomen, excessive sweating, muscle stiffness, reluctance to move, muscle twitching in the flank, a camped-out position, back muscle pain and/or a shortened stride. Sometimes this can happen very quickly or, in the cases with RER, some Standardbreds have been known to tie up 15 minutes after exercise. If your horse presents with these symptoms, call your veterinarian and do not move the horse but keep them standing.  Offer the horse water and prevent them from getting chilled with a blanket.  In cases of significant muscle damage, myoglobin (the protein which carries oxygen in the muscle cell) may be released, resulting in red or dark colored urine. Fluids, under the direction of your veterinarian, may be required to prevent kidney damage.

A horse who chronically ties up should be examined by a veterinarian to rule out specific diseases that could be the cause.  There is still much to learn about the causes of tying up, but research continues to offer new strategies to manage this difficult condition.