Designing perioperative analgesic regimen for ruminants is problematic as pain assessment is difficult and pregnancy adds additional considerations. The aim of this study was to assess the nociceptive properties of intramuscularly administered buprenorphine and transdermally administered fentanyl utilizing a composite pain score system. To better confirm that the observed abnormal behavior was related to pain, the current study attempted to characterize the nociceptive properties of the analgesic agents at a given plasma drug concentration, which has not previously been done. Additionally, the study characterized transplacental movement of analgesic agents via fetal plasma drug concentrations. In this study, we compared intramuscularly administered buprenorphine at a dose of 0.01 mg/kg every 8 hours for 48 hours starting at induction for surgery (n=6) to transdermal fentanyl patches (n=6) applied in the dorsal thorax region 24 hours before surgery at a dose of 2ug/kg/hr for postoperative pain. Ewe blood samples were collected and signs of pain and sedation were measured 24 hours before surgery (time -24), induction to surgery (time 0), and 2, 4, 6, 8, 12, 24, 36, 48 hours after. Using an indwelling fetal arterial catheter that was placed during the surgery, fetal blood pressure was recorded and blood samples were collected. Drug concentrations were measured in maternal and fetal plasma and amniotic fluid. The buprenorphine treated ewes exhibited more pain consistent behaviors than those treated with fentanyl, and their postoperative pain scores were significantly higher than the preoperative value. There were also significant differences in cardiovascular variables from the anesthesia records between the two groups. Overall, transdermal administration of fentanyl provided adequate analgesia with little adverse effects, making it a candidate for optimal postoperative pain management in sheep.
