In a survey published in 1999 by Lascelles and others(1) on the use of analgesics by British small animal veterinarians, some worrying results came to light. While analgesics were administered to 71% of surgeons to dogs and by 56% to cats undergoing laparotomy, only 22% would give small animals perioperative analgesia. Two factors were thought to account for this.
**veterinarians and veterinary nurses were not familiar enough with the small mammilian species and could not recognise signs of pain in them;
**dose regimens for analgesic drugs on small mammals and their possible side effects were not known.
It is indeed surprising how little there is published about pain assessment in small mammals in general, including rabbits. Only two authors can be found who have written about pain-related behavior in rabbits: Morton and others (2) in 1985 and Flecknell and others (3) in 2000. Their publications, however, are based on observations carried out on rabbits in a laboratory environment.
To date, no controlled study has been carried out to design a pain scoring system in rabbits in a clinical environment. Why is it so difficult to assess pain-related behavior in this species?
In the wild, rabbits are a "prey species". They cannot afford to show any signs of pain or distress, as this would only alert potential predators in search of an "easy catch". Therefore, a sick rabbit, or a rabbit in pain, will try to hide, staying still.
Pet rabbits have retained this instinct. Unfortunately, we are a potential predator for rabbits and so they tend to display this behavior in front of us.
The signs of pain described in rabbits are very variable-not all may be present at one time and no single sign can indicate the degree of pain. Signs will also vary between breeds and between individuals of the same breed. In addition, rabbits tend to change their behavior in the presence of humans, often remaining immobile.
The immediate response to acute pain is similar to other species: the animal tries to remove itself from the source of pain, it may vocalize and be aggressive, if restrained.
Following an accident or surgery, rabbits tend to reduce their activity, becoming completely immobile if suffering severe pain. They usually sit in the furthest corner of the cage and may even try to hide under the bedding. However, they may attempt to escape if handled, by kicking and scratching. Some rabbits will also show a shallow rapid respiration, grunting on expiration.
Rabbits in pain may fail to groom and, when moving, the gait may be altered, with a "tucked-up" appearance of the abdomen. They may also grind their teeth. If housed in groups, rabbits in pain will separate themselves from their cage-mates.
Water and food intakes tend to be reduced, as well as fecal output, and there may be a slight decrease in bodyweight. These reductions in appetite are very serious in rabbits, as they can result in gastrointestinal disturbances that can prove fatal if not treated appropriately (3).
Unfortunately, most of the signs described above are not only associated with pain, but also with stress. If pain is suspected in a rabbit, a positive response to the administration of an analgesic provides an easy test. Few studies, however, have been undertaken on the efficacy of analgesics in rabbits, and most information on effective dose rates and adverse effects has to be obtained from previous clinical experience (4).
Table 1 lists the analgesics that have previously been used in rabbits, and the suggested dose rates.
The duration of NSAIDS in rabbits is not known, although a duration of analgesia of up to 24 hours has been suggested for the stronger drugs. To date no reports of adverse reactions have been published (5). Until more information is obtained, however, prolonged use of these drugs should be avoided. Nevertheless , the author has used meloxicam at a dose of 0.2 ml/kg per os once daily for up to one month for the treatment of chronic dental pain, with no adverse effect.
These are used for managing major post-trauma or post-surgery pain. Buprenorphine is preferred for its longer duration of action (around eight hours). At the Easter Bush Veterinary Centre/Hospital for Small Animals, we are currently conducting, together with Boehringer Ingelheim, a controlled study on the efficacy of meloxicam as a perioperative analgesic in rabbits and we are also developing a pain scoring system for rabbits.
*** Analgesic drugs and dose rates used in rabbits ***
Acetyl salicylic acid: 100 mg/kg p.o.
Carprofen: 4mg/kg sc., s.i.d.; or 1.5 mg/kg p.o., b.i.d.
Flunixin: 1 mg/kg sc., b.i.d.
Ketoprofen: 3 mg/kg sc., s.i.d.
Meloxicam: 0.2 mg/kg sc., s.i.d.; 0.3 mg/kg p.o. s.i.d.
Piroxicam: 0.2 mg/kg p.o., t.i.d.
Buprenorphine: 0.01-0.05 mg/kg IM,SC,orIV; six-12 hourly
Butorphanol: 0.1-0.5mg/kg IM,SC,orIV; four-hourly
Morphine: 2-5mg /kg SC,IM; four-hourly
Pethidine(meperidine): 10mg/kg SC or IM; two-three hourly
*based mainly on clinical experience. Where not stated, frequency of dosing is not known. It is important to obtain an accurate weight on small
animals to ensure effective but safe dosing of analgesic drugs.
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