Identifying signs of pain is of the utmost importance when treating all patients in order to preserve animal welfare and fulfil our duty as veterinary professionals. However, sometimes it can be difficult to identify pain in our patients, especially those that hide signs of pain and illness as a protection mechanism against predators. In these cases, it is even more important to ensure your patients are not in pain in order to prevent suffering.
Exotic animal patients have unique ways of expressing and hiding pain, and it is our duty to identify when these patients are experiencing pain. Depending on the species, signs of pain can be subtle or even completely hidden. It is important to remember that all exotic animals feel pain. We should, therefore, assume that conditions considered painful in a canine or feline patient will also be painful to an exotic patient and treat them accordingly (Figure 1).
Small mammals
Recognising pain in small mammals
Small mammals are usually the easiest to assess for pain when considering exotic species, and several signs of pain can be identified across several species. These include increased twitching, orbital tightening (Figure 2), back arching (Figure 3), abdominal pressing, nose or cheek flattening and piloerection (Malik and Leach, 2017).
Several pain scales have been developed to assess visible signs of pain in rabbits (Keating et al., 2012), rats (Sotocina et al., 2011) and mice (Langford et al., 2010). These “grimace scales” use visual identifiers of pain to assign a level of pain or number score that can be vital to ensuring a patient receives an acceptable level of analgesia.
When assessing for signs of pain in small mammal patients, it is ideal to observe the patient in the most undisturbed state possible to fully observe the extent of any visible changes (Flecknell, 2018). Different types of pain have been shown to present in different ways in small mammal patients. For example, visceral pain is usually identified by belly pressing, staggering, a hollowed-out appearance of the flanks in guinea pigs and an arched spinal posture in rats (Flecknell, 2018).
Behavioural signs can also be used to identify signs of pain in small mammals. Decreased grooming behaviours, decreased feeding, restlessness and changes in temperament are all commonly observed signs of pain in small mammal patients (van Zeeland and Schoemaker, 2023) (Figure 4).
If there is any doubt that the patient is in pain, then analgesia should be administered without delay
Recently, pain scales such as the Bristol Rabbit Pain Scale (Benato et al., 2023) have been developed to allow veterinary professionals and owners alike to assess behaviours in small mammals and assign a numerical score to determine if the patient is painful or not. It is important to remember that all pain scales are subjective, whether based on visual identifiers or identified behaviours. This means that two evaluators who are presented with the same patient at the same time may score the patient differently depending on their interpretation of the scale. These pain scales are excellent guides for identifying pain in small mammals; however, the entire patient and its clinical presentation should be evaluated, and if there is any doubt that the patient is in pain, then analgesia should be administered without delay.
Pain management for small mammals
When considering analgesia options in small mammals, the options are vast. Depending on the species and drug evaluated, there are many efficacy studies for different classes of analgesia in small mammal patients. A comprehensive exotic animal formulary is ideal for accessing references for these studies and their associated dose rates (Carpenter and Harms, 2023). Small mammals often require far higher doses of commonly used analgesic drugs and at more regular intervals than canine and feline patients, so it is important to consult a formulary prior to prescribing.
Multimodal analgesia is recommended and if possible, analgesia should be provided prior to the painful stimulus (eg before surgery). Analgesia options in small mammals are plentiful, including opioids, non-steroidal anti-inflammatories (NSAIDs), local anaesthesia (administered topically or intravenously), gabapentin, paracetamol, ketamine and tramadol. In particular, analgesia should be used amply in hindgut fermenters as pain is a well-known cause of gastrointestinal stasis.
Birds
Recognising pain in avian patients
Signs of pain can be more subtle in avian patients compared to small mammal patients, and subtle cases can often require an experienced eye, familiar with the normal behaviours of the species presented.
Birds often hide signs of pain to avoid predation but also to mask signs of inferiority to other birds of the same species (Douglas et al., 2018). Commonly observed signs of pain in birds include a hunched posture, lethargy, piloerection of the feathers, closed eyes, poor feather appearance and a tucked-up abdomen (Paul-Murphy and Hawkins, 2015) (Figure 5). Pelvic limb injuries may result in lameness, difficulty perching or stumbling; meanwhile, pectoral limb injuries may present as a dropped wing or feather plucking over the affected area (Malik and Valentine, 2017).
Changes in behaviour can also be observed in avian patients experiencing pain. These include aggression in patients that previously have not been aggressive or submissive behaviours in previously aggressive animals. Feather plucking can give clues as to the source of pain, as some birds will pluck feathers over an area of pain or discomfort. However, this must be observed with caution, as feather plucking is a highly multifactorial issue and misinterpretation of signs can occur in these cases.
Pain management for avian patients
Veterinarians often do not know where to start when providing analgesia to avian patients. Their anatomy and physiology is far removed from that of mammals, and often they require different classes of drug and much higher dose rates. Historically, most avian patients have been reported to have a higher proportion of kappa opioid receptors compared to mu opioid receptors, and as a result, butorphanol has long been recommended for analgesia in avian patients. However, more recent research has identified that this is not the case for all birds and that the distribution of opioid receptors differs vastly between species (Fousse et al., 2020), which has implications for the efficacy of opioid analgesia between avian species.
Recent research has identified […] that the distribution of opioid receptors differs vastly between species, which has implications for the efficacy of opioid analgesia
For example, American kestrels have been shown to demonstrate a dose-dependent increase in thermal withdrawal times when administered hydromorphone intramuscularly (Guzman et al., 2013). However, when fentanyl was administered intramuscularly to umbrella cockatoos, no increase in thermal withdrawal times was observed until the birds were administered a 10-times higher dose than that provided to canine and feline patients, which was also associated with significant hyperactivity (Hoppes et al., 2003). Buprenorphine has been demonstrated to provide analgesia in American kestrels at doses from 0.1 to 0.6mg/kg (Ceulemans et al., 2014); however, similar doses did not provide an analgesic effect in African grey parrots (Paul-Murphy et al., 1999).
Studies for many different analgesic agents are available for various species and orders of birds. Tramadol has been shown to be an effective analgesic in many avian orders, as have various NSAIDs including meloxicam. However, doses are often dramatically increased compared to those for canine and feline patients. For example, tramadol required doses of 30mg/kg to reach therapeutic plasma levels in Hispanolian Amazon parrots (Souza et al., 2012), and meloxicam doses of up to 2mg/kg were required in pigeons for post-operative analgesia (Desmarchelier et al., 2012).
Multimodal analgesia should also be used in avian patients, and the use of local anaesthesia for infiltration or nerve blocks can be a useful adjunct to oral or injectable analgesia.
Reptiles
Recognising pain in reptiles
Reptile patients are by far the most difficult to assess compared to other exotic patients. Pain studies are often few and far between, and there are vast differences in anatomy and physiology between different orders of reptiles, as well as in their differing perception of pain. For example, while a thermal withdrawal stimulus elicits a quick response in mammals, and avian patients will withdraw from a hot stimulus, reptiles have been known to sustain severe thermal burns by sitting on heated elements for hours at a time.
FIGURE (6) A leopard gecko displaying a hunched posture indicative of pain the day after exploratory laparotomy and ovariohysterectomy, just prior to being administered a pure mu opioid
While most clinicians choose to extrapolate from other species to determine which procedures or illnesses may be painful for reptile patients, several signs of pain in reptiles have been described. These include a decreased interaction with the environment, decreased appetite, decreased range of motion in injured limbs, altered basking behaviours, aggression and skin colour changes in lizards who are capable of this behaviour (Latney, 2023). Overt physical signs are uncommon in reptiles compared to other exotic species, but can include squinting or closing of the eyes and a hunched posture, arched back or lameness (Figure 6).
Pain management in reptiles
There is a paucity of data for the provision of analgesia in reptiles, and studies demonstrating analgesic efficacy are few and far between.
Some of the most important considerations for providing analgesia are species differences, the temperature of the patient and its preferred optimum temperature zone, at which temperature it will best metabolise drugs, and the presence of a renal portal system, which affects where drugs can be administered (Mosley, 2011). It is recommended that any injectable drugs are administered cranial to the kidneys in order to reduce the effects of first-pass metabolism. Route of administration is also important, as this can affect the bioavailability of drugs. For example, ketoprofen administered to green iguanas had a 28 percent reduction in bioavailability when administered intramuscularly compared to intravenously (Tuttle et al., 2006).
Some of the most important considerations for providing analgesia [to reptiles] are species differences, the temperature of the patient and its preferred optimum temperature zone, at which temperature it will best metabolise drugs, and the presence of a renal portal system
The three primary classes of analgesia drugs administered to reptiles include opioids, NSAIDs and local anaesthetics. In general, pure mu opioid drugs have been shown to provide effective analgesia for the majority of reptile patients (Sladky, 2023). Morphine has been shown to be effective for analgesia in some reptile species, while buprenorphine and butorphanol have failed to provide reliable analgesia in reptile patients (Mosley, 2011). Tramadol has been shown to provide long-lasting analgesia in chelonians and lizards for up to 96 hours in some cases (Cummings et al., 2009). The efficacy of NSAIDs in reptiles is difficult to interpret as pain responses are hard to measure and the measurement of plasma concentrations does not always correlate to tissue concentrations or guaranteed efficacy. Local anaesthesia can be used in reptile patients, with local blocks, nerve blocks and even epidural protocols described (Sladky, 2023).
Multimodal analgesia is advocated in reptiles, as knowledge of effective analgesic agents is poor at this time.
Conclusion
Recognising pain in exotic species can be difficult, even with the use of verified pain scales. It is important to extrapolate from knowledge of other species and consider that an exotic patient may be in pain despite the lack of clinical signs. Commonly used analgesic drugs in companion animal practice can be used in all exotic species; however, a comprehensive formulary should be consulted first as dose rates and dose intervals can vary drastically between species and some drugs may lack efficacy in some species, particularly reptile species.
