Effects of the continuous rate infusion of propofol with or without fentanyl on ruminal motility in calves.

This study aimed to evaluate ruminal motility before, during, and after propofol anesthesia with or without fentanyl in Holstein calves by investigating effects of these anesthetic protocols on rumen function and cardiorespiratory variables. This study employed a randomized crossover design with a 1-week washout period between treatments and included eight calves aged 6-12 months and weighing 100-180 kg. Animals received either propofol alone (propofol group [PG]) or propofol with fentanyl (propofol-fentanyl group [FG]), alternating the order of treatments between groups. Anesthesia was induced with propofol (5.0 mg/kg IV) in the PG and with propofol (4.0 mg/kg IV) and fentanyl (0.001 mg/kg IV) in the FG. Next, anesthesia was maintained for 60 min by the continuous infusion of propofol (0.6 mg/kg/min IV) alone in the PG or combined with fentanyl (0.001 mg/kg/h IV) in the FG. Cardiorespiratory variables were recorded at baseline and every 15 min during anesthesia. Ruminal motility was assessed before fasting, after fasting, during anesthesia, and throughout recovery until contractions returned to baseline values. We noted that the median (minimum/maximum) ruminal normalization time did not differ significantly between the PG (35 [10/50] min) and FG (45 [20/120] min) (P = 0.19). Food withholding and handling-related stress reduced ruminal motility in both groups. Both protocols completely suppressed ruminal contractions during anesthesia, with contractions beginning to return approximately 10 min after the end of infusion in the PG and 20 min in the FG. Furthermore, propofol caused hypoventilation and respiratory acidosis while maintaining hemodynamic variables within clinically acceptable limits. In summary, fentanyl addition was not associated with a statistically significant prolongation of ruminal-motility recovery, although the wider range of the ruminal normalization time observed in the FG suggests individual variability, warranting further investigation.