Equine Health Library

Senior Horse

Health Conditions

Neurologic | Gastrointestinal | Respiratory

Help Prevent Neurological Diseases


The neurologic form of EHV-1 is rare and is not preventable with vaccination. Preventing the spread of the respiratory EHV-1 is paramount in keeping exposure down among horses.

Affected horses typically DO NOT show outward signs of respiratory disease associated with EHV-1 but do exhibit fever and depression in addition to neurologic deficits.

No EHV-1 vaccine is labeled to prevent EHM, but vaccination using a high-antigen load EHV-1 vaccine such as Prestige® Prodigy® may help decrease the severity of clinical disease and reduce nasal shedding in infected horses. The frequency of vaccination in high-risk horses is a controversial topic with many sources recommending revaccination every four to six months.

Other diseases that can affect your senior horse’s central nervous system are easily preventable through vaccination. These are Eastern Equine Encephalitis, Western Equine Encephalitis, West Nile virus and rabies. To a lesser extent, senior horses may suffer neurologic deficits due to EPM, tumors or parasites that migrate to the brain.

If your horse shows signs of incoordination or clumsiness, call your veterinarian immediately. If you see a change in your horse that you’re not sure is normal, please call your veterinarian for a diagnosis. Depression, reluctance to eat and trouble getting up are all good reasons for a veterinary evaluation.

Download the Equine Health Library Senior Horse Special Needs Record.

Equine Protozoal Myelopathy

Most cases of Equine Protozoal Myelopathy (EPM) are caused by Sarcocystis neurona, which starts in the opossum and ends in the horse through contaminated hay or forage. In the U.S., the incidence of EPM has remained relatively steady. The geographic range matches that of the opossum, though contaminated hay could ship and expose horses beyond the opossum’s natural domain.

Risk factors include:

  • Age, with mature horses more commonly affected than very young horses
  • Career or lifestyle, with a higher incidence among horses used for racing or western performance
  • Recent stress event such as long-distance transportation or illness
  • Season, with increased numbers of cases identified during late summer and fall
  • Management practices that include not protecting horse feeds from opossums and/or leaving pet food in the barn as an opossum attractant
  • Barns and pastures in close proximity to wooded terrain
  • History of other cases of EPM on the farm

Clinical Signs

Clinical signs vary quite a bit and include:

  • Ataxia (unsteady gait)
  • Weakness
  • Muscle atrophy (typically asymmetrical)
  • Cranial nerve deficits (including inability to swallow)
  • Decreased tongue tone
  • Ear or eyelid droop
  • Head tilt
  • Blindness
  • Seizures (rarely)

Diagnosis and treatment

In addition to a complete neurologic exam, your veterinarian will diagnose EPM with cervical radiographs to rule out cervical arthritis or cervical vertebral stenotic myelopathy and a spinal tap and blood test to look for Sarcocystis neurona-specific antibodies. Early detection of EPM is critical to optimize your horse’s chances for complete recovery. Approximately 30 percent of affected horses will make a complete recovery, yet most are able to successfully return to their former riding discipline.

Therapy involves daily administration of an anti-protozoal drug. Duration of therapy varies based on the individual horse’s response to the medication.

Click here for more information on FDA-approved Protazil® (1.56% diclazuril) Antiprotozoal Pellets for the treatment of EPM.

Important Safety Information

PROTAZIL® is contraindicated in horses with known hypersensitivity to diclazuril. The safety of Protazil in horses used for breeding purposes, during pregnancy, or in lactating mares, and use with concomitant therapies in horses has not been evaluated. Do not use in horses intended for human consumption. Not for human use. For complete safety information, refer to the product label.


Senior horses have multiple risks for developing gastrointestinal problems. The three primary causes – choke, colic and cancer – can create catastrophic problems. Poor dentition can lead to problems chewing and masticating feed increasing choke risk. Also, fatty tumors that wrap around the intestines can lead to colic. Esophageal obstruction (choke), colic and other tumors can lead to cancer in senior horses.


Older horses can experience a variety of dental problems, including sharp points on their molars, missing teeth, and a misaligned bite or wave mouth. All of these can lead to increased difficulty chewing and masticating long-stemmed feed, which can increase the risk of choke.

During an episode of choke, a bolus of food becomes lodged in the esophagus, resulting in gagging, profuse salivation and possibly nasal discharge. Luckily, choke is not normally life threatening, but prompt attention from your veterinarian is a must.

Dental issues also may increase the risk of impaction colic, so make sure your senior horse’s teeth are examined by your veterinarian at least once per year.


Older horses also are more susceptible to colic caused by strangulating lipomas – fatty tumors with long stalks of attachment that wrap around sections of the intestines. The complete obstruction of the intestine results in colic that usually requires surgery to resolve. Some seniors also experience colic and weight loss associated with forms of cancer, including lymphosarcoma.


Your veterinarian may be able to detect some forms of cancer with a rectal exam to search for enlarged internal lymph nodes and other internal masses. Gray horses are at increased risk for melanomas that might become larger and more invasive with advancing age.


Some statistics suggest that up to 80 percent of gray horses older than 15 years of age will develop at least one melanoma, while the overall incidence among the general horse population is only three to 15 percent.

Melanomas are malignant tumors that can be locally invasive as well as metastatic (spread internally to distant sites). These tumors are often progressive and can have an unpredictable pattern of growth. Common sites for external melanomas include the genitalia and areas under the tail and surrounding the anus. External melanomas can vary in appearance from flat to wart-like to pedunculated (attached to the skin by a stalk).

Horses can also have internal melanomas in areas such as the abdominal cavity, lymph nodes, salivary glands, mammary glands, the vertebral column and the eye.


Treatment can be difficult, especially in advanced cases involving multiple, large, and/or internal melanomas. Your veterinarian may recommend one or more of the following: Surgical excision, immunostimulant vaccines, intralesional chemotherapy or systemic treatment with cimetidine. Melanomas, even small ones, should not be ignored. Your veterinarian will help determine the most appropriate course of treatment.


Equine asthma is the most commonly diagnosed respiratory condition in older horses. This is because repeated bouts of airway inflammation throughout the years can lead to long-term physical changes within the airway.

Help your horse breathe easier.

Inflammation may be a result of infection or, more commonly, environmental allergens and irritants. You may notice a cough, nasal discharge, exercise intolerance and wheezing during exertion. If so, try making changes in management and diet, such as wetting down hay to reduce dust and better ventilating your barn. More severely affected horses may require bronchodilators and/or steroid therapy.

Talk to your veterinarian if your horse’s condition is worsening.