3 Equine Difficulty in Eating NOTES

Objectives

• Recognize clinical signs related to prehension, mastication, and dysphagia.
• Generate differential diagnoses.
• Develop a diagnostic plan based on the identified problem and differentials.
• Know how to treat choke in horses.
• Understand management strategies for horses that are unable to eat.

Equine GI Anatomy & Physiology

• Eating involves prehension, mastication, and swallowing.

Prehension

• Prehension is grasping food with the lips and incisors.
• Sensory input relies on:
  • Olfactory (smell) via cranial nerve 1
  • Optic (sight) via cranial nerve 2
  • Sensation via trigeminal nerve 5
• Motor input is managed by the facial nerve 7 for lip movement.

Mastication

• Mastication is chewing, involves cheek teeth, tongue, and buccal muscles.
• Requires cranial nerves:
  • Trigeminal nerve 5 (motor to muscles of mastication, sensory to buccal mucosa and teeth)
  • Facial nerve 7 (motor to facial expression muscles, sensory to cranial 2/3 of tongue, parasympathetic fibers to salivary glands)
  • Hypoglossal nerve 12 (motor to tongue)

Swallowing

• Swallowing is complex, involving pharyngeal and esophageal functions.
• Nerves 9 (glossopharyngeal), 10 (vagus), 11 (accessory), and 12 (hypoglossal) provide sensor and motor function to the pharynx and larynx.
• Vagus nerve branches innervate the esophagus.

Normal Esophagus

• The esophagus in an adult horse is 120 cm long.
  • 70 cm in the cervical neck
  • 50 cm within the thorax
  • 5 cm in the abdomen
• The proximal 2/3 of the esophagus contains striated skeletal muscle, and the distal 1/3 contains smooth muscle, bookended by upper and lower esophageal sphincters.
• The narrowest points in the lumen diameter are at the post-pharyngeal region, thoracic inlet, and base of the heart.

Difficulty Eating

• Dysphagia refers to difficulty swallowing, while difficulties of eating is a broader term.
• The basic approach includes history, physical examination, and observing the horse eat different foods to identify issues with prehension, mastication, or swallowing.
• Differentiate eating problems from anorexia.
• Rabies can cause issues with prehension, mastication, or swallowing if clinical signs are present for less than 14 days.

Problems With Prehension

• Clinical signs involve difficulty grasping food and pulling it into the mouth, without nasal or tracheal discharge.

Diseases Affecting Prehension

• Neurological diseases can impact cranial nerves 5 and/or 7, such as trauma, EPM, or temporohyoid osteoarthropathy leading to facial nerve paralysis, though most horses with unilateral facial nerve paralysis can still prehend food.
• Yellow Star Thistle/Russian knapweed causes nigropallidal encephalomalacia leads to an inability to prehend food due to poor coordination of the lips and tongue.
  • Horses may still be able to swallow and can drink by immersing their head in water.
  • This condition is associated with hypertonicity of facial muscles and necrosis of the globus pallidus and substantia nigra on necropsy and has no treatment.
• HYPP, botulism, and tetanus can affect prehension, mastication, and swallowing.

Anatomical Problems Affecting Prehension

• Fractures of the rostral mandible or maxilla.
• Ulcers on the mucosa (vesicular stomatitis, a reportable disease).
• Tumors of the mandible or maxilla.
• Parrot mouth, where the maxilla is longer than the mandible.

Problems With Mastication

• Clinical signs: Dropping food from the mouth (quidding) without nasal or tracheal involvement.

Anatomical Problems Affecting Mastication

• Issues include abnormal dentition, tongue lacerations, fractures of the maxilla or mandible, and TMJ pain, with abnormal dentition being the primary cause.
• Dental abnormalities include wave mouth, step mouth, hooks, and smooth mouth. Sharp points on teeth can lead to mucosal ulcers and pain.

Neurological Problems Affecting Mastication

• Diseases affecting cranial nerves 5, 7, and 12.
• Rabies, EPM, trauma, brainstem tumor or abscess, HYPP, botulism, and tetanus.

Problems With Swallowing (Dysphagia)

• Clinical signs include food or saliva coming out of the mouth, green nasal discharge (food), and coughing while eating (aspiration).
• Diagnostics include:
  • Passing a nasogastric tube to rule out esophageal choke.
  • Endoscopic examination of the pharynx/larynx and esophagus.
  • Radiographs or contrast radiographs of the pharynx/larynx or esophagus.
• Swallowing can be divided into pharyngeal and esophageal phases.

Pharyngeal Dysfunction

• Normally, the epiglottis is dorsal to the soft palate, and the horse can reposition the epiglottis when swallowing.
• A persistently dorsally displaced soft palate indicates a functional or neurological issue.

Neurological/Functional Problems with Swallowing

• Guttural pouch mycosis affecting CN 9-12.
• Botulism, rabies, tetanus, and viral encephalitis (EEE, WNV) causing lesions in the cerebrum or brainstem.
• EPM.
• Trauma to nerves or muscles (basisphenoid fracture, rupture of longus capitus muscles).
• Hyperkalemic periodic paralysis.
• White muscle disease.
• Lead toxicity.
• Dysautonomia/grass sickness.

Morphologic Abnormalities with Swallowing

• Cleft palate.
• Retropharyngeal abscess.
• Trauma or foreign bodies causing soft tissue swelling.
• Chondritis, subepiglottic cysts, and entrapped epiglottis.
• These can also result in upper respiratory problems.

Esophageal Dysfunction

• The most common cause of dysphagia concerning the esophagus is choke (obstruction) and its sequelae, such as diverticulum, stricture, and rupture.
• Neurological problems are not common in horses.

Simple Esophageal Obstruction

• Clinical signs are dysphagia, food from the nose/mouth, aspiration, retching, head and neck extension, and agitation.
• Risk factors include poor mastication and eating too fast.
• Diagnosis: a nasogastric tube can pass into the esophagus but not into the stomach.

Treatment of Choke

• Sedation to relax the esophagus and keeping the head down to prevent aspiration pneumonia.
• Careful, slow pumping of water when a nasogastric tube is against the obstruction to flush food into the stomach, which may come out of the nose.
• Medications to relax the esophagus:
  • Buscopan (N-butylscopolammonium bromide) for short-term smooth muscle relaxation and anticholinergic effects.
  • Oxytocin.
  • Intraluminal lidocaine.
  • NSAIDs to decrease inflammation/edema.
• Antibiotics for aspiration pneumonia prevention/treatment.
• Fluid therapy may be needed for long-duration choke.

Complications of Choke

• Ulcers lead to strictures, diverticula, and rupture.
• Endoscopy can help assess trauma to the esophagus after choke resolution.
• Long-lasting choke may cause severe electrolyte abnormalities, dehydration, and azotemia, with loss of Na and Cl, leading to hypochloremic metabolic alkalosis.
• Pneumonia/pleuropneumonia.

Slaframine (""Slobber Toxin"")

• Results from ingesting moldy red clover.
• Causes excessive salivation without difficulty eating.

Management of Eating Problems

• Resolve or address the underlying disorder.
• Dietary modifications to improve the horse's ability to eat.
• Address prehension difficulties by trying different foods.
  • Horses with hay bag issues may be able to eat from the ground or from a pelleted slurry.
• Address mastication issues with a slurry of complete pelleted feeds, such as Equine Senior.
• Address swallowing difficulties more aggressively, removing free water and feed if there is significant aspiration pneumonia.
• Nasogastric tube feeding with well-ground pelleted feeds or commercial liquid diets like Well-Gel (Purina) or Platinum Performance Enteral Nutrition.
• Horses transiently develop metabolic acidosis due to loss of HCO3 that turns into metabolic alkalosis due to loss of chloride.
• Hyponatremia can occur as well.