Effects of fentanyl administration on locomotor response in horses with the G57C µ-opioid receptor polymorphism

Lois A. Wetmore, Peter J Pascoe, Yael Shilo-Benjamini, Jane C. Lindsey

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


OBJECTIVE To determine the locomotor response to the administration of fentanyl in horses with and without the G57C polymorphism of the µ-opioid receptor. ANIMALS 20 horses of various breeds and ages (10 horses heterozygous for the G57C polymorphism and 10 age-, breed-, and sex-matched horses that did not have the G57C polymorphism). PROCEDURES The number of steps each horse took was counted over consecutive 2-minute periods for 20 minutes to determine a baseline value. The horse then received a bolus of fentanyl (20 µg/kg, IV), and the number of steps was again counted during consecutive 2-minute periods for 60 minutes. The mean baseline value was subtracted from each 2-minute period after fentanyl administration; step counts with negative values were assigned a value of 0. Data were analyzed by use of a repeated-measures ANOVA. RESULTS Data for 19 of 20 horses (10 horses with the G57C polymorphism and 9 control horses without the G57C polymorphism) were included in the analysis. Horses with the G57C polymorphism had a significant increase in locomotor activity, compared with results for horses without the polymorphism. There was a significant group-by-time interaction. CONCLUSIONS AND CLINICAL RELEVANCE Horses heterozygous for the G57C polymorphism of the µ-opioid receptor had an increased locomotor response to fentanyl administration, compared with the response for horses without this polymorphism. The clinical impact of this finding should be investigated.

Original languageEnglish (US)
Pages (from-to)828-832
Number of pages5
JournalAmerican Journal of Veterinary Research
Issue number8
StatePublished - Aug 1 2016

ASJC Scopus subject areas

  • veterinary(all)


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