The use of opioids in birds of prey pain relief: a world to be explored

  The evaluation and methods of pain treatment in prey birds (species belonging to the orders Falconiformes, Accipitriformes and Strigiformes), such as the use of opioids, is still little explored in the scientific literature in all its research potential, in particular on the order Strigiformes, and most of the studies covered species of the orders Accipitriformes and Falconiformes (MAZOR-THOMAS, MANN, KARAS & TSENG, 2014; D’OVIDIO, NOVIELLO & ADAMI, 2015).

    Opioid drugs act through their ability to bind to central and occasionally peripheral opioid receptors (LIERZ & KORBEL, 2012). Although mammals and birds have δ, κ and μ opioid receptors in similar proportions, κ receptors seem to be of critical importance in the analgesia of birds in general (LARIOS & MADERA, 2019). Thus, butorphanol, which acts as an agonist on κ receptors and μ receptor antagonist, has been the analgesic drug most used in sedation and analgesia protocols in these animals (MASSONE, 2011; SILVA et al., 2017), although it may achieve a "ceiling effect", after which the increased dose will not provide greater analgesic effect (HAWKINS & PAUL-MURPHY, 2011). Lierz & Korbel (2012) claim, however, that butorphanol may cause respiratory depression and reduced gastrointestinal motility in the gyrfalcon (Falco rusticolus). Riggs et al (2008), in a study including red-tailed buzzards (Buteo jamaicensis) and great-horned-owl (Bubo virginianus), reached a half-life of 0.93 and 1.78 hours for each species, respectively, followed by the administration of 0.5 mg/kg of butorphanol IV. For the administration of the same dose by intramuscular route, the values found were 56 minutes and 24 seconds (0.94 hours) and 1 hour, 50 minutes and 24 seconds (1.84 hours), respectively. The same study found higher values of plasma concentration of butorphanol in the aurochs when compared with the values found in red-tailed owls, a fact that the author related to the higher heart rate of the owls. 

    Lopes (2022), in a work using sixteen tropical screech owls (Megascops choliba), evaluated responses to environmental stimuli, duration of anesthetic and analgesic effects and monitoring of physiological parameters in the isolated use of intranasal midazolam compared to its association with intranasal butorphanol. The study concluded that the combination of drugs did not promote advantageous effects in terms of duration and intensity, and there was a significant reduction in heart rate, respiratory rate and cloacal temperature in both groups. The fact that the association of midazolam and butorphanol was better succeeded in cockatiels (Nymphicus hollandicus) (DOSS et al., 2018), suggests that differences in metabolism and anesthetic effects between bird species need to be better explored.

   Tramadol is also used in anesthetic protocols for birds of prey (DE JESUS, 2021; SOUZA et al., 2009), because despite having low affinity for μ receptors, its mechanism of action involves the inhibition of other neurotransmitters, acting as α 2-agonists in terms of pain control (LARIOS & MADERA, 2019).  It is important to note that the physiological and clinical effects of opioid use can be affected by a considerable number of variables, such as individual factors, route of administration and commercial drug preparation (HAWKINS & PAUL-MURPHY, 2011).

   In addition to opioid substances, non-steroidal anti-inflammatory drugs (NSAIDs) are also frequently used in the analgesia of poultry in general, such as meloxicam, which acts on the control of inflammatory pain, but has the same renal and gastrointestinal as seen in mammals, should be used with caution. Meloxicam may have nephrotoxic effects during periods of hypotension (GRESPAN & ROSA, 2014; GUZMÁN et al, 2023), and its use as a preanesthetic agent is not recommended. Thus, this agent acts as a good method of control of postoperative pain (LARIOS & MADERA, 2019).

   In general, studies on the recognition and management of pain in wild and exotic species have been developed more frequently (LIERZ & KORBEL, 2012; LUDDERS, 2017). Thus, it is essential to recognize its importance for the advancement of veterinary clinical practice and further progress in the search for knowledge in this area.

Author: Amanda de Castro -GEAS Brasil Deputy Director of Internal Communications. 

Review: Iago Junqueira  - GEAS BRASIL partner by The Wild Place.

Wild panel/February 2025.

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