Jeske Noordergraaf, VMD

October 2006

I have in the past several months seen several horses with the presenting complaint of being down and being unable or unwilling to get up.  Three of these horses had been absolutely fine the day before, one had even been ridden.  What would cause this?  There are a number of diseases that can present with these signs, although most horses with neurologic diseases are up and walking. 

As veterinarians, our first goal is to determine whether the nervous system is involved in causing the problem.  Colicky horses may lie down but they are usually willing to get up, and once up, walk normally.  The second goal is to determine the anatomical location involved, and the third goal is to do diagnostics and treat the horse without anyone, including the horse, getting hurt. 

To determine where the focal point of the disease is, we use the signs the horse is exhibiting.  A horse that has problems with coordination usually has a problem with the spinal cord.  A problem with balance suggests a disease in the vestibular system or brain.  A change in the horse’s alertness or mentation usually comes from damage to the brain. 

Trauma can be the cause when a horse flips over or falls down.  Vertebrae can be crushed or broken when a horse has an accident.  If the horse flips over and lands on the poll of its head, one vertebra may crush the next one, severing the spinal cord and causing death.  Often we don’t know what horses do when we aren’t watching them, which makes determining the cause harder.

There are a number of diseases that damage the brain or spinal cord.  I will discuss several of the more common.  The season of the year plays a part in the diagnosis. 

Mosquito-borne diseases are possible during bug season and for a short time afterwards. These include West Nile Virus and Eastern, Western and Venezuelan Encephalitis. The virus attacks the brain causing depression, ataxia, and all the other signs we see.  Luckily there are vaccinations to prevent these diseases.  These horses usually have trouble walking, are wobbly, may be found down already and be unable to either get up or stay standing.  Very severe cases may even have seizures.  There is no specific treatment for these diseases; we treat the horses with supportive care and anti-inflammatory drugs, hoping that their immune system will fight off the infection.

Equine Protozoal Myelitis (EPM) is a disease that affects the spinal cord.  Horses become infected when eating opossum feces, usually hidden in hay.  The causing agent, Sarcocystis Neurona, lives in the spinal cord, where it causes damage.  Presenting signs range from muscle loss in just one area to lameness, dragging just one leg to having seizures.  Usually the onset is gradual, but exposure may have been years before the clinical signs appear.  For this disease there is a fairly new vaccine and a treatment.  The company that makes the treatment considers the treatment a success if the horse improves by one lameness grade, but the horse may not become completely normal again.

Wobbler Syndrome, or cervical stenotic myelopathy, is a problem with the vertebrae in the neck.  Either the vertebral canal is narrower then normal, putting pressure on the spinal cord, or there can be arthritic changes present, again putting pressure on the cord.  These horses are usually bright and alert, but the history may be that the horse is very clumsy.  Trauma may make the condition much worse.  Diagnosis involves x-rays of the neck with contrast material.  This is seen more in rapidly growing horses.  The underlying cause is not completely known but nutrition may play a part in the development. 

Equine herpes virus-1, also known as rhinopneumonitis or rhino for short, can cause respiratory disease or abortion in pregnant mares.  A third form of the disease can affect the brain, causing neurologic disease.  Usually there is an acute onset of hind limb ataxia.  There may also be paralysis of the urinary bladder, with urine dripping.  This is a characteristic finding.  The ataxia usually starts in the hind limbs but may progress to the front legs also.  For this disease there is no preventative vaccine which is labeled for this form of the rhino virus, but some of the vaccines seem more effective than others.  The history is usually that there has been a respiratory outbreak on the farm and then horses start with ataxia problems.   Prevention involves isolating the horses that are traveling and making sure all the horses are vaccinated for rhino.

Rabies is always a possibility when the brain is involved.  A rabid animal will walk up to a horse in the middle of the pasture during the day and bite.  Horses with rabies usually show a change in their mentation or attitude; they become ataxic and may go down.  There is no treatment for rabies once signs appear but there is a good vaccine available.  Be careful putting your hand in the mouth, as rabies can be transmitted from your horse to you. 

All of these neurologic diseases are serious and the cause can be hard to determine.  The longer that a horse is down, the worse the prognosis becomes.  If you notice that your horse is walking funny, isn’t very stable on his feet or is lying down, get your veterinarian out quickly.  Although there aren’t many specific treatments for these diseases, anti-inflammatory drugs such as banamine, dexamethasone and DMSO can reduce the swelling in the brain and spinal cord and hopefully help your horse.