Videofluoroscopy shows clinically relevant changes in swallow metrics and esophageal transit in normal horses with xylazine, anticholinergic use, and varied feed consistency.

Videofluoroscopy was used to study swallowing and esophageal movement in healthy horses to see how sedatives, anticholinergic drugs, and different food textures affect swallowing and esophageal transit.

Study Purpose and Design

• The research aimed to examine how different feed textures and drug treatments affect the three phases of swallowing in horses.
• Specific drugs studied included xylazine (a sedative) and N-butylscopolammonium bromide (an anticholinergic drug), both commonly used in veterinary medicine.
• The study also aimed to characterize esophageal motility after administering barium contrast medium via a nasoesophageal tube—this helps visualize swallowing and esophageal transit during videofluoroscopy.
• 8 healthy horses participated over approximately 2.5 weeks, undergoing videofluoroscopic swallow studies before and after treatment interventions.

Methods and Measurements

• Videofluoroscopy (a real-time x-ray movie) was used to observe the swallowing process and esophageal transit of barium-laden food and liquids.
• Feedstuffs of three consistencies (liquid, intermediate, and solid) were mixed with barium to visualize how different viscosities transit through the esophagus.
• Swallowing phases and esophageal transit rates were assessed by adapting swallow metrics from canine models, given similarities in physiology and prior groundwork in veterinary diagnostics.
• Barium was also administered directly into the esophagus through a nasoesophageal tube to assess baseline esophageal motility without the confounding effect of chewing or swallowing.

Key Findings

• Effect of Xylazine:
  • Xylazine caused a significant reduction in the cranial esophageal transit rate. Specifically, the transit of barium from the cranial esophagus was slower after xylazine administration compared to no treatment (estimated reduction of ~0.018 m/s).
  • This indicates that xylazine sedation prolongs the time food takes to move through the early part of the esophagus.
  • Slower esophageal transit was more pronounced with thicker (higher viscosity) feed consistencies following xylazine administration.
• Effect of Feed Consistency:
  • Liquid barium passed faster through the cranial esophagus than intermediate or solid consistencies, showing that increasing viscosity slows down the initial esophageal transit.
  • No significant differences were observed in the transit rate from the thoracic inlet (mid-esophagus region) to the caudal esophagus regardless of treatment or feed consistency.
• Effect of N-butylscopolammonium Bromide:
  • This anticholinergic drug increased the incidence of bolus retention — meaning horses showed delayed or impaired clearance of the barium bolus in the esophagus.
  • Bolus retention may suggest disruptions in normal esophageal motility caused by this drug.
• Esophageal Motility and Nasoesophageal Tube:
  • Contrast pooling was noted at the thoracic inlet when barium was administered through the nasoesophageal tube before esophageal peristalsis started.
  • This suggests that initial holding or stasis of contrast material can occur post-intubation, which is important to consider when interpreting videofluoroscopy results.

Conclusions and Implications

• Administration of xylazine sedative delays bolus transit through the upper esophagus in horses, with more marked effects on thicker feeds.
• Use of N-butylscopolammonium bromide can increase the risk of bolus retention, indicating potential adverse effects on esophageal motility.
• Videofluoroscopy in horses is a practical and informative method to assess swallowing mechanics and identify esophageal disorders or dysphagia (difficulty swallowing).
• Naso-esophageal intubation with barium contrast is effective but may temporarily affect normal esophageal flow, highlighting the need for careful interpretation during diagnostic imaging.
• This research helps refine veterinary diagnostic protocols and drug use understanding for equine patients with swallowing or esophageal motility issues.