Neurologic Problems in the Foal
Nothing disrupts the joy of foal ownership like the observation of potential problems: A disinterest in nursing, a depressed attitude, strange mannerisms, or seizures could mean a foal is suffering from some serious neurologic problems. During a presentation at the 2011 Western Veterinary Conference, held Feb. 20-24 in Las Vegas, Nev., Mary Rose Paradis, DVM, MS, Dipl. ACVIM, an associate professor in the Department of Clinical Sciences at Tufts University's Cummings School of Veterinary Medicine, in North Grafton, Mass., discussed some of the common problems that neurologic foals exhibit along with diagnostic methods and treatments.
Besides the common signs of depression and seizures, the resting foal might thrash his legs at seemingly random times, or he might make paddling motions with his legs as he walks; the foal might display back muscle spasms (known as opisthotonos, seen in the foal as hypertension/arching of the back to one side) or show extensor muscle rigidity; or he might overheat (hyperthermia), she added.
Neurologic Exams in Foals
"The most common neurologic presenting complaints in the newborn foal are changes in normal behavior, lack of suckle, depression, and seizures," Paradis explained.
A neurologic examinations of a foal differ from those performed on adult horses, Paradis said, and it might yield slightly different results:
- The cranial nerve examination, which involves determining response to quick hand movement toward the eye (whether he flinches), is probably not as useful as it is in the adult horse, because it will likely show a foal has a lack of menace response), Paradis said. This menace response is a learned behavior that develops in the first few weeks of life;
- A abnormal position of the pupil--generally an indicator of cranial nerve problem in the adult horse--is not uncommon in foals less than a month old, she said. Neonates often have a slow pupilary light response due to increased sympathetic nerve tone from excitement;
- Paradis explained that some foals--healthy or not--don't respond to the "slap" test, which involves slapping the left side of the thorax (the part of the body between the neck and the diaphragm, located near the chest) gently with the open hand. This should result in the muscles larynx (opening to the trachea) adducting (drawing inward), and this can be felt as a 'flicking' or movement in the throatlatch region;
- Exaggerated head movement is typically associated with neurologic problems in adult horses, but this is normal in foals as they respond to external stimuli, Paradis said; and
- Foals tend of display more exaggerated limb reflexes than adult horses, she added.
Whereas gait analysis is generally performed in hand, on a longe line, or under saddle in the adult horse, Paradis suggested watching a foal's gaits while he is "freely moving about the stall or paddock."
A depressed foal lacks a response to external stimuli and spends an unusually large amount of time sleeping, Paradis said. It's important to understand that healthy foals can spend about half their day napping, so consider how he responds to typical external stimuli before assuming a sleepy foal is depressed.
"Seizures in the first few days of life of the foal can be acquired or congenital (born with it) in origin," Paradis said, adding that acquired seizures are generally related to perinatal asphyxia (lack of oxygen in a neonate during the birth process), infection, or trauma; congenital causes include abnormally formed neurologic or skeletal tissue or a genetic defect.
Neonatal Encephalopathy (NE)
Paradis said NE (also called neonatal maladjustment syndrome or dummy foal syndrome) is the most common acquired--as opposed to congenital--neurologic problem seen in foals. She noted that while researchers are not certain about what causes NE, they believe that some type of asphyxiation plays a role in the disorder's development--simply put, the foal's brain is deprived of enough oxygen during birth, whether through chronic placental insufficiency or acute placental separation, leading to abnormalities. Paradis said most foals (70%-80%) with NE recover and lead a healthy life.
Another less-frequent cause of seizures in the foal is bacterial meningitis, which Paradis explained is a form of septicemia. In the neonate's central nervous system, the blood-brain barrier--that which generally protects the brain from harmful cells circulating in the blood--is incomplete. This situation is compounded by the foal's relative lack of phagocytes, which are white blood cells that engulf and digest bacterial invaders.
"Once bacterial entry has occurred," Paradis noted, "cerebrospinal fluid (CSF) acts as a good media for bacterial growth. Rapid multiplication of the bacteria is favored because of the inadequate ... defenses of the CNS."
Paradis said that many foals with neurologic problems have a history of trauma, specifically of the head and neck.
"Cerebral trauma (cases) will have signs of blindness, depression, seizure, head pressing, and coma," Paradis described.
She continued to explain that brain stem trauma will be accompanied by signs of nystagmus (involuntary movement of the eyeballs), facial paralysis, strabismus (misalignment of the eyeballs within the sockets), and gait abnormalities. Clinical signs of neck trauma or intracranial hemorrhage include ataxia (incoordination), and paralysis.
Congenital Neurologic Issues
Several congenital neurologic problems affect foals, Paradis said:
- Benign pediatric epilepsy has been observed primarily in Arabians and Half-Arabians (particularly from the Egyptian line), Paradis explained. These foals appear normal between seizures, and most will "grow out of the problem," she added;
- Lavender foal syndrome is found in Egyptian Arabian foals almost exclusively. Common clinical signs in affected foals are seizures, opisthotonos, stiff and paddling leg movements, nystagmus, and a soft lavender coat color. This disorder is fatal for neonates; and
- Narcolepsy is sometimes found in Miniature Horses. Paradis said that foals tend to collapse--or fall asleep--when nursing or during handling. Some foals, she said, grew out of the disorder.
Paradis described several diagnostic options for veterinarians addressing neurologic problems in foals:
- For foals suffering from seizures, a blood gas analysis and chemistry profile can either confirm or rule out certain causes of the seizures such as hypoxemia, acidosis, and hepatic encephalopathy), she said;
- A CSF analysis is the test of choice if a veterinarian suspects septic meningitis;
- Radiographs (X rays) are helpful for diagnosing cerebral or spinal trauma or malformation, she said, adding that some of these issues might also be evident through palpation; and
- CT scans and MRIs are becoming more popular for checking neurologic tissue of the brain and spinal cord.
"The most important ... therapy for the neurologic foal is supportive care," Paradis stressed. She explained that a stomach tube will be the easiest way to ensure the foal receives proper nutrition during treatment, and that recumbent foals should be monitored closely for pressure sores. The foal will also need to be kept warm and dry, a task that can prove difficult as the foal may urinate on itself when unconscious, causing urine scalding.
Medical treatment for seizures (generally controlled by sedatives diazepam or midazolam) and antibiotics for controlling meningitis is warranted. Paradis emphasized, though, that the foal should have attentive nursing care to prevent additional problems/injuries.
Because foals tend to "grow out" of some neurologic problems, depending on the disorder, the prognosis can be a positive one. Paradis relayed that foals with NE specifically have a good prognosis, with survival rates as high as 80%. Many of these foals, she added, have grown up to have successful careers under saddle.
Foals with septic meningitis, however, have a less favorable chance for survival. She explained that if the foal does survive his illness, "there is a chance it will have a mental disability that may make it untrainable." She added that a new group of drugs (called third-generation cephalosporins) have shown promise for treating meningitis, however, and if they continue to yield positive results, "this picture may change."
About the Author
Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.