As far as the authors are aware, this is the first study reporting the use of butorphanol as an epidural analgesic agent in dromedary camels. Results of the present study revealed that the period of analgesia was greatly extended by administering butorphanol (synthetic opioid) together with lidocaine (local anesthetic) in dromedary camels. Similar findings were reported in horses, where the period of epidural analgesia was extended by seven times when butorphanol and lidocaine were given together (136 minutes), compared to lidocaine alone (36 minutes). [16]. It seemed that addition of an opioid would account for intensifying and prolonging the loco-regional blockade provided by the local anesthetic agents [17, 18].
In this study, epidural butorphanol showed delayed onset of analgesia compared with butorphanol - lidocaine mixture or lidocaine and the butorphanol - lidocaine mixture revealed the longest duration of analgesia. This might be attributed to the poor lipid solubility and sluggish dispersion of butorphanol towards the opioid receptors in the dorsal horn of the spinal cord causing slower onset, slower clearance and subsequently long-lasting analgesia [19, 20]. The potentiated analgesic effects of butorphanol - lidocaine mixture may also due to the synergy and the multimodal analgesic mechanisms of lidocaine and butorphanol [20].
An appropriate epidural procedure should be harmless and devoid of locomotor disturbances or recumbency. As epidural opioids induce analgesia without blocking of the spinal motor functions, it is judicious to assume that no adverse effects on gait would be associated with the pharmacological actions of butorphanol [6]. Results of the present study accentuate the epidural co-administration of butorphanol as a safe analgesic agent, where camels received butorphanol did not develop ataxia or any other adverse effects after the epidural treatment. The signs of mild motor disturbances reported in camels received lidocaine and butorphanol – lidocaine treatments could be attributed to the sensory and motor blockade induced by lidocaine [16]. In calves, the subarachnoid administration of butorphanol – lidocaine mixture induced serious motor disturbances and animals were reluctant to stand during the study [15]. This could be related to the use of a higher dose of lidocaine (4 mg kg− 1), the different route of administration (subarachnoid route) or the species difference. In sheep, the intra-thecal administration of butorphanol was accompanied by adverse behavioral changes and signs of neurological disorders [21].
In the current study, camels given epidural butorphanol and butorphanol – lidocaine mixture exhibited signs of slight sedation in the form of mild change in the head position and mild drooping of the lower lip. Those signs could be due to the forward dispersal of butorphanol into the central circulation or cranial dissemination of butorphanol into the central nervous system via the cerebrospinal fluid resulting into systemic effects (sedation). Our findings are in congruent with previous studies in horses [16] and calves [15].
The frequency of respiration, the number of heart beats, and rectal temperature measurements in this study were not significantly altered in comparison with the baseline values in all camels throughout the study. This is largely matching with other studies, where no cardiovascular alterations were observed after epidural administration of butorphanol in dogs [22] or horses [16]. On the contrary, in calves [15], significant rise in heart rate was reported. The discrepancy in findings between studies may be attributed to the species difference, the dose of the given agent or the route of drug administration.
No significant variations in the hematological or biochemical parameters were reported in all camels post epidural administration of all treatments, compared with the baseline values. These findings are similar to previous outcomes recorded when butorphanol was administrated via the intravenous route in camels [14]. A transient rise in glucose level was observed after all treatments, which returned to basal levels 24 hours later. The increased glucose values may be due to the release of adrenocortical hormones and initiation of glycogenolysis in liver and muscles [15, 23].
We did not observe any signs of tympany or abdominal discomfort due to impaction in any of the camels, and camels passed fecal piles without difficulty post epidural administration of all agents. This contradicts previous studies, where in ponies, butorphanol caused decreased jejunal propulsive motility [24] and in horses, butorphanol resulted into marked decrease in the fecal production accompanied by abdominal discomfort [25]. The inconsistency in findings between studies may be attributable to a physiologic difference between ponies, horses and camels, the dose of injectate or the route of drug administration.