Regardless of whether your mare delivers a seemingly healthy foal or something is not quite right, it’s critical you have your veterinarian conduct a post-foaling exam of the neonate. This examination should include a neurologic assessment.
When conducting a neurologic exam on a foal, veterinarians look for subtle and obvious signs of abnormalities that can point to disease in various parts of the nervous system. Monica Aleman, MVZ, PhD, Dipl. ACVIM (LAIM and Neurology), professor of equine internal medicine and neurology at the University of California, Davis, reviewed the key parts of this exam during a presentation at the 2020 American Association of Equine Practitioners’ Convention, held virtually.
Neurologic Exam Basics
The goals when performing a neurologic exam on a foal, said Aleman, are to determine whether the animal is normal or abnormal and, if the latter, to pinpoint the affected area and narrow down possible causes. Veterinarians can easily perform it in conjunction with the post-foaling physical exam to gain more information about the foal’s overall clinical status, she said.
The skills and tools needed: Observation, palpation, listening, and familiarity with normal major milestones in neonatal and developing foals, Aleman said.
“Know what is normal, repeat the examination when possible, and be thorough and consistent so important parts of the exam aren’t missed,” she said.
Milestones that indicate a normal transition from intrauterine to extrauterine life include:
- Sternal recumbency (lying upright) within 1 to 2 minutes of birth
- Being alert and responsive to stimuli within 5 minutes
- Suckle reflex within 20 minutes (the foal extends his tongue and curls it, perhaps making sucking noises)
- Nickering in response to dam’s nickering with 30 minutes
- Standing within an hour
- Nursing within two hours
Deviations from these events and timepoints can signify something’s wrong. Other parameters vets can assess to determine whether a foal needs medical attention include heart rate, respiration, mucous membrane color and capillary refill time, muscle tone, and response to nasal stimulation, ear tickle, and back scratch.
Areas of Evaluation
There’s no strict order or method for carrying out a neurologic exam on a foal, said Aleman. “You can do it any way you want as long as you are thorough and consistent so you don’t forget essential parts,” she said.
Those essential areas of evaluation include
- Behavior: “The foal should be very curious and responsive to the environment,” said Aleman.
- State of consciousness: Abnormal states of consciousness, in order from least to most severe, include quiet, obtunded (fairly unresponsive to stimuli)), stupor (unresponsive to moderate stimuli but responds to more painful sensations such as hard pinching of the skin), and coma (unresponsive to any stimuli).
- Cranial nerves: To assess foals’ cranial nerve function (their reactions and reflexes), veterinarians look at menace response (whether the foal blinks when you wave a hand toward his eye—this learned response develops by seven days of age), left and right facial sensation, suckle reflex, dazzle reflex (whether the foal blinks when you shine a very strong light in his eye), pupillary light reflex, hearing (clapping to see if the foal jerks his head), among others. “Foals should have full vision and hearing at birth,” said Aleman.
- Spinal reflexes: For a veterinarian to assess spinal reflexes, the foal must be completely relaxed—in lateral recumbency (lying on one side) and non-weight-bearing, she said. He or she gently taps on the foal’s biceps, triceps, flexor tendons, pelvic limbs, trunk, and anal and perineal areas to test for a response.
- Posture: Observe the foal’s head and neck position; stance; and urination and defecation posture. Neonates’ head and neck should be upright, and they usually have a wide stance that becomes more square as they mature, Aleman said.
- Gait evaluation: Foals are amazingly coordinated at birth—an evolutionary trait that allows them to run away from predators, said Aleman. A healthy neonate’s gait could be bouncy, but practitioners should know what’s normal for a particular breed (e.g., gaited horses such as Paso Finos will be smoother), she said.
- Nociception: Only perform this step to assess a foal’s conscious perception of pain if he displays no voluntary movement, she said.
- Palpation: Veterinarians can use their hands to detect possible areas of pain, asymmetry, sweating, or anything else that’s not obvious visually.
Signs of Neurologic Disease
Different clinical signs indicate disease in different areas of the nervous system. These areas and their associated signs include:
Cerebrothalamus (forebrain): This region comprises the cerebrum and is responsible for cortical awareness and motor and sensory functions. Signs of disease include:
- Altered behavior, or any compulsive behaviors, strange vocalizations, “stargazing,” or sudden aggressive or subdued behaviors;
- Cortical blindness, when the eye appears normal but the foal is blind;
- Proprioceptive (awareness of one’s limbs and position) deficits; and
- Altered motor function.
“You may have one, two, three, or all of these signs,” said Aleman. “But just one is enough to localize to this area.”
Brainstem: This structure at the base of the brain is responsible for consciousness and involuntary actions such as breathing and heartbeat. Signs of brainstem disease include:
- Altered state of consciousness;
- Multiple cranial nerve deficits;
- Central vestibular disease;
- Cardiovascular/respiratory/sleep center disorders (“Foals should never sleep standing,” said Aleman. “This is very abnormal as neonates.”); and
- Proprioceptive deficits.
“You can have one, two, three, or more of these signs,” she said, “but usually if have one or more, you have an altered state of consciousness.”
Cerebellum: This structure is located at the back of the brain and is involved in motor coordination. Signs of cerebellar disease include:
- Hypermetria (an exaggerated gait);
- Ataxia (incoordination);
- Intention tremors, which only occur when the animal performs an intended movement such as walk or eat;
- Lack of menace response;
- Anisocoria (differences in pupil size, not always seen);
- Proprioceptive deficits
Vestibular system: This is responsible for balance and eye movements. Signs of disease include:
- Head tilt;
- Nystagmus (rapid involuntary eye movements);
- Ventral strabismus (abnormal eye position);
- Circling; and
Spinal cord: This allows the body and the brain to communicate with one another. Signs of spinal cord dysfunction could be sensory (proprioceptive deficits or ataxia) or motor (dysmetria, paresis/paralysis, weakness), she said.
Neuromuscular junctions: These connect muscles to nerves and allow them to communicate. Signs of dysfunction include:
- Most commonly, weakness;
- Functional deficits such as paralysis, dysphagia, proprioceptive deficits, gait deficits, and reflex deficits; and
- Physical deficits such as muscle atrophy (wasting).
The most common neuromuscular disease in foals is botulism, said Aleman.
She said it’s important to note that the presence of proprioceptive deficits alone does not help veterinarians localize disease, because these deficits can be present with brain, spinal cord, and peripheral (nerves located elsewhere) disease.
“Take all clinical signs and parameters into account when determining the cause of a foal’s neurologic issues and potential courses of action,” said Aleman. “Neurologic examination in the foal is easy to perform and provides useful information of the overall health status.”