Evaluation of the effects of the opioid agonist morphine on gastrointestinal tract function in horses

Am J Vet Res. 2006 Jun;67(6):992-7. doi: 10.2460/ajvr.67.6.992.


Objective: To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses.

Animals: 5 horses.

Procedures: Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic.

Results: Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean +/- SD defecation frequency decreased from 3.1 +/- 1 bowel movements in control horses to 0.9 +/- 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 +/- 0.7 kg to 1.1 +/- 0.7 kg, fecal moisture content decreased from 76 +/- 2.7% to 73.5 +/- 2.9%, and borborygmus score decreased from 13.2 +/- 2.9 to 6.3 +/- 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses.

Conclusions and clinical relevance: Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics, Opioid / pharmacology*
  • Animals
  • Cross-Over Studies
  • Feces / chemistry
  • Gastrointestinal Contents / drug effects
  • Gastrointestinal Tract / drug effects*
  • Gastrointestinal Tract / physiology*
  • Gastrointestinal Transit / drug effects*
  • Horses / metabolism*
  • Male
  • Morphine / pharmacology*
  • Water / analysis


  • Analgesics, Opioid
  • Water
  • Morphine