Pain and analgesia in pet rabbits within the veterinary environment: a review

Comparison of the effects of intranasal and intramuscular midazolam-butorphanol-ketamine on intraocular pressure, tear production and sedation in New Zealand White rabbits

OBJECTIVE

To compare the effects of intranasal (IN) and intramuscular (IM) midazolam-butorphanol-ketamine on intraocular pressure (IOP), tear production (TP) and sedation in rabbits.

STUDY DESIGN

Prospective, randomized, crossover experimental study.

ANIMALS

Fourteen male New Zealand White rabbits, aged 1-2 years, body mass 3.1 ± 0.8 kg (mean ± standard deviation).

METHODS

Rabbits were administered midazolam (1 mg kg-1), butorphanol (1.5 mg kg-1) and ketamine (5 mg kg-1) via IN and IM routes. IOP, TP and sedation scores were assessed at 0 (before drug administration), 5, 15, 30, 45 and 60 minutes after drug administration. Heart rate (HR), respiratory rate (fR), rectal temperature (RT), noninvasive mean arterial blood pressure (MAP) and peripheral hemoglobin oxygen saturation (SpO2) were simultaneously recorded until 45 minutes after drug administration. The onset and duration of sedation and sedation scores were recorded.

RESULTS

Drug delivery route had no significant impact on mean IOP (p = 0.271) or TP (p = 0.062), and there were no significant changes over time for IOP (p = 0.711) or TP (p = 0.372). Similarly, delivery route had no significant impact on HR (p = 0.747), fR (p = 0.872), RT (p = 0.379), MAP (p = 0.217) and SpO2 (p = 0.254). Sedation onset was faster with IN (3.0 ± 1.0 minutes) than with IM administration (4.9 ± 0.7 minutes) (p = 0.011), but sedation duration was significantly longer with IM (52.6 ± 7.2 minutes) than with IN delivery (30.7 ± 6.8 minutes) (p = 0.004). There was no significant difference in sedation scores between the two delivery routes at any of the recorded time points.

CONCLUSIONS AND CLINICAL RELEVANCE

The combination of midazolam-butorphanol-ketamine had minimal impact on physiological and ocular variables regardless of the route of administration, whereas IN drug administration led to a shorter onset and duration of action than IM administration.

Comparison between Carprofen and Meloxicam for Post-Neutering Pain Management in Pet Rabbits

Surgical neutering in pet rabbits is common practice to prevent reproduction and associated health issues. Adequate postoperative pain management is crucial for recovery, yet effective methods in clinical settings remain underexplored. This study compared the analgesic effects of carprofen and meloxicam in pet rabbits undergoing surgical neutering. Fifty rabbits of varied demographics were included, with pain assessed using the Centro Animali Non Convenzionali Rabbit Scale (CANCRS). Rabbits were allocated to receive postoperative 2 mg kg-1 carprofen or 1 mg kg-1 meloxicam by subcutaneous injection. Anesthesia was induced with an intramuscular combination of ketamine (20 mg kg-1), medetomidine (0.4 mg kg-1), and butorphanol (0.2 mg kg-1), and ovariectomy or orchiectomy were performed. The CANCRS scale was used to assess pain by evaluating the rabbit preoperatively, 6 h postoperatively, and at three time points the following day. Times of return to spontaneous feeding and fecal production were also recorded. No statistically significant difference was found between treatment groups based on CANCRS scores and resumption of food intake and fecal output. No clinically detectable adverse effects were noted. While limitations include the use of a single pain assessment scale and the absence of a placebo control group, the results suggest that both carprofen and meloxicam can be viable options in clinical practice. Further research utilizing diverse pain assessment methods is warranted to enhance understanding and optimize pain management strategies for rabbits undergoing surgical procedures.

An investigation into how accurately UK rabbit owners identify pain in their pet rabbits

BACKGROUND

Rabbits are popular family pets. They are prey species and so have evolved to hide signs of illness and pain. Recent research has developed robust pain scales for use in a clinical setting, but to date none has examined rabbit owners' ability to recognise pain in their animals. This study investigated how owners identify pain in their pet rabbits and their ability to correctly identify different levels of pain, in order to determine any need for owner education in this area.

METHODS

Owners were recruited via Facebook and a two-part online survey was distributed. Part one collected data on demographics, owners' knowledge of pain signs and beliefs about pain in rabbits. Part two asked respondents to pain score eight videos of rabbits in different levels of pain for comparison to pain scores made by three experts. We used a simplified version of the Bristol Rabbit Pain Score (BRPS) which involved a single 0 to 3 scale. We explored the number of pain signs each respondent could list, the total score given to the videos, and their deviation from the experts' scores.

RESULTS

A total of 500 respondents completed part one of the survey and 345 additionally completed Part two. Respondents were on average able to state five signs of pain (range 0-12), but females stated significantly more (p = 0.018), as did those who worked with rabbits (p = 0.004) and those with experience of their rabbit having an operation (p = 0.01). Overall, 98.6% of respondents thought rabbits felt pain as much or more that dogs and cats. In Part two, respondents more frequently agreed with the experts when identifying rabbits in no pain (88.8%) and severe pain (65.2%), but there was lower agreement when identifying mild (28.4%) and moderate pain (43.2%). Respondents overall rated pain lower than experts with an average total pain score of 11.9 compared to 18 given by the experts.

CONCLUSIONS

Most rabbit owners are able to list numerous pain signs and are generally able to identify pain-free rabbits and those in severe pain. Owners' ability to differentiate between mild and moderate pain is more limited and could benefit from training in the subtler signs of pain. Veterinary professionals are well placed to educate owners about signs of pain in rabbits and should be aware of areas where owners' knowledge can be improved.

Transversus Abdominis Plane (TAP) Block in Rabbit Cadavers: Anatomical Description and Measurements of Injectate Spread Using One- and Two-Point Approaches

The aim of this study was to describe one-point (preiliac approach) and two-point (preiliac and retrocostal approach) blocks of the Transversus Abdominis Plane (TAP) on a cadaveric model. For this purpose, ultrasound-guided infiltration of the plane between the internal oblique and transversus abdominis muscles was performed and, after dissection of tissues, the areas and percentage of nerve fibers involved were analyzed. Injection into the TAP plexus of a 1 mL/kg solution of 2% lidocaine and 1% methylene blue (1:1) was performed in 30 rabbit cadavers. In fifteen rabbits (group S), the solution was inoculated at the preiliac level. In the other 15 rabbits (group D), the solution was divided into two inoculations (0.5 mL/kg at the retrocostal level and 0.5 mL/kg at the preiliac level). All cadavers were then dissected and stained spinal nerve branches were measured. Moreover, the percentage of length, height and the total area of the stained tissue were calculated. In the S group, T10, T11 and T12 nerve eminences were successfully stained in 18%, 52% and 75% of cases, respectively. Furthermore, L1, L2, L3 and L4 were stained in 95%, 100%, 60% and 40% of cases, respectively. In group D, the ventromedial eminence of T10, T11 and T12 were stained in 68.1%, 100% and 98% of cases, respectively, and L1, L2, L3 and L4 were stained in 88%, 100%, 62% and 31% of cases, respectively. In conclusion, a two-point TAP block is more effective in covering the nerve eminences of the cranial abdomen than the preiliac approach alone.

Use of 3D-printed polylactic acid/bioceramic composite scaffolds for bone tissue engineering in preclinical in vivo studies: A systematic review

3D-printed composite scaffolds have emerged as an alternative to deal with existing limitations when facing bone reconstruction. The aim of the study was to systematically review the feasibility of using PLA/bioceramic composite scaffolds manufactured by 3D-printing technologies as bone grafting materials in preclinical in vivo studies. Electronic databases were searched using specific search terms, and thirteen manuscripts were selected after screening. The synthesis of the scaffolds was carried out using mainly extrusion-based techniques. Likewise, hydroxyapatite was the most used bioceramic for synthesizing composites with a PLA matrix. Among the selected studies, seven were conducted in rats and six in rabbits, but the high variability that exists regarding the experimental process made it difficult to compare them. Regarding the results, PLA/Bioceramic composite scaffolds have shown to be biocompatible and mechanically resistant. Preclinical studies elucidated the ability of the scaffolds to be used as bone grafts, allowing bone growing without adverse reactions. In conclusion, PLA/Bioceramics scaffolds have been demonstrated to be a promising alternative for treating bone defects. Nevertheless, more care should be taken when designing and performing in vivo trials, since the lack of standardization of the processes, which prevents the comparison of the results and reduces the quality of the information. STATEMENT OF SIGNIFICANCE: 3D-printed polylactic acid/bioceramic composite scaffolds have emerged as an alternative to deal with existing limitations when facing bone reconstruction. Since preclinical in vivo studies with animal models represent a mandatory step for clinical translation, the present manuscript analyzed and discussed not only those aspects related to the selection of the bioceramic material, the synthesis of the implants and their characterization. But provides a new approach to understand how the design and perform of clinical trials, as well as the selection of the analysis methods, may affect the obtained results, by covering authors' knowledgebase from veterinary medicine to biomaterial science. Thus, this study aims to systematically review the feasibility of using polylactic acid/bioceramic scaffolds as grafting materials in preclinical trials.

Determining a cut-off point for intervention analgesia in rabbits using the Bristol Rabbit Pain Scale

BACKGROUND

The objective of this study was to determine the threshold of the Bristol Rabbit Pain Scale (BRPS) indicating the need for intervention analgesia.

METHODS

Fourteen members of veterinary staff were recruited to rate rabbits (n = 71) in acute pain. Observers in group A (n = 7) were asked to score each rabbit using the BRPS, while observers in group B (n = 7) independently answered the question 'In your clinical capacity, do you think this animal requires analgesia?' with either 'Yes' or 'No'. The answers from the two groups were then compared.

RESULTS

Rabbits for which group B answered 'No' (n = 36) had a median BRPS score (range) of 4 (0-10), while those for which group B answered 'Yes' (n = 42) had a median BRPS score of 9 (1-18; Z = -7.48; p < 0.001). The area under the receiver operating characteristic curve was 0.85 (95% confidence interval: 0.77-0.93; p < 0.001), indicating excellent discrimination of the BRPS with a cut-off score of 5.5 (sensitivity 88.1% and specificity 69.4%). However, for practicality, a score of 5 was deemed a feasible cut-off.

LIMITATIONS

The main limitations of this study are the small rabbit sample size and the subjective nature of pain scoring in animals.

CONCLUSIONS

Analgesic intervention should be considered in rabbits with a pain score equal to or greater than 5 on the BRPS.

Deep learning for video-based automated pain recognition in rabbits

Despite the wide range of uses of rabbits (Oryctolagus cuniculus) as experimental models for pain, as well as their increasing popularity as pets, pain assessment in rabbits is understudied. This study is the first to address automated detection of acute postoperative pain in rabbits. Using a dataset of video footage of n = 28 rabbits before (no pain) and after surgery (pain), we present an AI model for pain recognition using both the facial area and the body posture and reaching accuracy of above 87%. We apply a combination of 1 sec interval sampling with the Grayscale Short-Term stacking (GrayST) to incorporate temporal information for video classification at frame level and a frame selection technique to better exploit the availability of video data.

Intranasal Atomization of Ketamine, Medetomidine and Butorphanol in Pet Rabbits Using a Mucosal Atomization Device

A non-invasive method of drug delivery, intranasal atomization, has shown positive results in human medicine and in some animal species. The objective of this study was to evaluate the effects of intranasal atomization, compared to intramuscular administration, of a mix of anesthetic drugs in pet rabbits. In total, 104 mixed-breed pet rabbits, undergoing various types of surgery, received a combination of ketamine, medetomidine, and butorphanol (20, 0.4, and 0.2 mg/kg) by intranasal atomization using a Mucosal Atomization Device (Group MAD) or intramuscular administration (Group IM). When required, isoflurane was dispensed through a face mask. At the end of the procedures, atipamezole was administered using the same routes in the respective Groups. There were no differences in time to loss of righting reflex between the groups, while differences were found for the need for isoflurane (higher in Group MAD) and recovery time, occurring earlier in Group MAD. The results suggest that intranasal atomization of a combination of ketamine, medetomidine, and butorphanol produces a lighter depth of anesthesia in pet rabbits, compared to intramuscular administration. Intranasal atomization can be performed to administer sedative and anesthetic drugs, avoiding the algic stimulus related to the intramuscular inoculation of drugs.

Pain Recognition in Rabbits

Rabbits typically undergo at least one painful procedure during their lifetime and appropriate methods of assessment are essential to reduce or alleviate pain. Various methods of assessing pain in rabbits have been investigated, with the validity of spontaneous behavior and grimace scale scoring being the most studied to date. Assessment of pain is challenging, compounded by rabbits being a prey species that display freezing behavior in the presence of unfamiliar caregivers. Here we discuss some key changes in rabbits that can be used in the assessment of pain and provide some practical suggestions to ensure that the assessment can be carried out effectively.

Intramuscular alfaxalone with or without buprenorphine or hydromorphone provides sedation with minimal adverse effects in healthy rabbits (Oryctolagus cuniculus) in a randomized blinded controlled trial

OBJECTIVE

To evaluate the effects of alfaxalone administered IM with or without buprenorphine or hydromorphone in healthy rabbits (Oryctolagus cuniculus).

ANIMALS

24 male rabbits undergoing elective orchiectomy between August 21, 2021, and November 6, 2021.

PROCEDURES

In this controlled clinical trial, rabbits were randomly assigned to receive alfaxalone (4 mg/kg, IM) alone (group A; n = 8) or with buprenorphine (0.03 mg/kg, IM; group BA; 8) or hydromorphone (0.1 mg/kg, IM; group HA; 8). Vital signs and sedation scores were recorded immediately prior to (T0) and 10 minutes after (T1) treatment. Ease of IV catheter placement and pain scores were also evaluated. All rabbits received ketamine (2.5 mg/kg, IV), midazolam (0.13 mg/kg, IV), and meloxicam (0.5 mg/kg, SC) before orchiectomy but after IM treatments. Results were compared across groups with ANOVA or Fisher exact tests and across time with paired t tests.

RESULTS

Sedation score, median time to recumbency, and ease of catheter placement did not differ among groups. Supraglottic airway device placement was possible for 1 rabbit in group A, 1 in group BA, and 2 in group HA. Mean respiratory rate at T1 versus T0 was significantly decreased for groups BA (63.8 vs 128.6 breaths/min) and HA (66.7 vs 123.2 breaths/min). Mean postoperative pain scores were significantly lower for rabbits in group HA (0.58), compared with those in groups A (2.25) and BA (2.06).

CLINICAL RELEVANCE

All 3 treatments provided reliable sedation; however, alfaxalone (4 mg/kg, IM) combined with hydromorphone (0.1 mg/kg, IM) may be a better choice for painful procedures.

Effect of preemptive topical application of lidocaine or prilocaine-lidocaine on successful catheterization of ear veins in New Zealand White rabbits

OBJECTIVE

To compare 5% lidocaine ointment applied for 10 minutes before intravenous (IV) catheterization to a eutectic mixture of local anesthetics (2.5% lidocaine and 2.5% prilocaine; EMLA) cream applied for 10 or 60 minutes prior and a water-based placebo for 60 minutes for successful marginal ear IV catheterization in rabbits.

STUDY DESIGN

Randomized, blinded, complete crossover, controlled trial.

ANIMALS

A total of 10 intact male, New Zealand White rabbits aged 4 months.

METHODS

After application of one of the treatments on the marginal ear vein, an operator unaware of the treatment attempted IV catheter placement. Successful IV catheterization was considered as a catheter inserted at the first attempt, safely secured, with appropriate patency. Generalized linear mixed models were developed to identify relevant predictors of successful catheter placement.

RESULTS

Ears that had EMLA cream applied 60 minutes before the catheterization attempt had more than 10 times the odds of successful catheter placement [odds ratio (OR)=10.75; 95% confidence interval (CI), 1.92-60.16; p < 0.008] compared with placebo. Both the application of EMLA cream or lidocaine ointment 10 minutes before the catheterization attempt resulted in approximately three times the odds of successful catheter placement compared with placebo, but were not statistically significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Application of EMLA cream on the marginal ear vein 60 minutes before catheterization increases the chance of successful IV catheter placement in conscious rabbits.

Validation of the rabbit pain behaviour scale (RPBS) to assess acute postoperative pain in rabbits (Oryctolagus cuniculus)

Considering the widespread use of rabbits in research that potentially causes pain and discomfort and the limited number of pain assessment validated tools in this species, we aimed to develop and validate a scale of acute postoperative pain in rabbits (RPBS). Footage of 58 rabbits from previous studies were used, recorded at 'baseline' (before orthopaedic and soft tissue surgeries), 'pain' (after surgery), 'analgesia' (after analgesic), and '24h post' (24 hours after surgery). The videos were randomised and assessed twice by four evaluators, within one-month interval between evaluations. After content validation, RBPS was further refined using the criteria from the validation. According to the principal component analysis, RPBS was considered unidimensional. The intra- and inter-observer reliability was excellent (ICC>0.80) for all evaluators. There was a high Spearman's correlation of the RPBS with unidimensional scales (>0.80) and a moderate correlation with the Rabbit Grimace Scale (0.68), confirming criterion validity. According to the mixed linear model, the scale was responsive, shown by the increase in pain scores after surgery. Construct validity was confirmed by known-group approach and internal relationships among items. Adequate item-total correlation (>0.3) was observed for all items, except for the attention to the affected area (0.04). The internal consistency was very good (Cronbach's α coefficient = 0.78; Mcdonald's ω coefficient = 0.83). The cut-off score for rescue analgesia was ≥3, with an area under the curve >0.95, demonstrating a high discriminatory capacity of the instrument. Scores 3 and 4 were within the uncertainty diagnostic zone. Specificity was 87% and sensitivity was 90%. It was concluded that the RPBS presented content, criterion, and construct validities, responsiveness, and reliability to assess acute pain in rabbits submitted to orthopaedic and soft tissue surgeries. The cut-off for rescue analgesia serves as a basis for the administration of analgesics to rabbits submitted to painful procedures.

Ultrasound-Guided Saphenous Nerve Block in Rabbits (Oryctolagus cuniculus): A Cadaveric Study Comparing Two Injectate Volumes

Simple Summary

General anesthesia in rabbits is associated with significantly higher mortality than in dogs and cats. In addition, as prey animals, rabbits tend to mask signs of pain, making early detection particularly difficult. Loco-regional anesthesia represents a fundamental component of a multimodal approach to pain management and is an effective strategy to reduce the need for systemic anesthetic and analgesic drugs, thereby limiting their associated side effects. The saphenous nerve is the largest sensory branch of the femoral nerve and provides sensory supply to areas of the hind-limb. Saphenous nerve blockade allows for analgesia of the front and inner parts of the pelvic limb without affecting femoral nerve motor function, thus allowing optimal pain relief but permitting continued mobilization, which may be of particular importance in rabbits as it allows preservation of normal physiological prey behavior (e.g., hiding, kicking). This cadaveric study describes an ultrasound-guided saphenous nerve block technique in rabbits and compares the length of the nerves stained following injection of two different dye volumes. The results show that both volumes consistently stained the saphenous but not the femoral nerve. This technique has the potential to provide hind-limb analgesia while preserving femoral motor function in rabbits.

Abstract

Ultrasound-guided (US-guided) loco-regional anesthesia techniques allow direct visualization and blockade of sensory nerves. The saphenous nerve (SN), a terminal branch of the femoral nerve (FN), is strictly a sensory nerve for which electrical locator devices are ineffective for localization as no effector muscle contractions can be evoked. US-guided SN block in species other than rabbits produces hind-limb analgesia without affecting FN motor function. The aims of this study were to develop a US-guided SN block technique in rabbits and to compare the spread obtained using two different dye volumes. Twelve hind-limbs from six cadavers (1.6 ± 0.1 kg) were included; after randomization, the SN block was performed on the right or left hind-limb, injecting 0.05 mL kg⁻¹ or 0.1 mL kg⁻¹ of tissue dye in lidocaine (1:50 v:v). Subsequent dissections allowed nerve staining measurements. All SNs were identified, and 17.8 ± 4.6% and 31.0 ± 8.9% of the SN length were stained using low-volume and high-volume of the dye, respectively. Regardless of the volume used, the SN was consistently stained while the motor branch of the FN was not. This US-guided technique may provide hind-limb analgesia without affecting FN motor function in rabbits undergoing mid-distal hind-limb surgeries.

Effects of a Single Opioid Dose on Gastrointestinal Motility in Rabbits (Oryctolagus cuniculus): Comparisons among Morphine, Butorphanol, and Tramadol

The aim of this study was to evaluate and compare the effects of single doses of butorphanol, morphine, and tramadol on gastrointestinal motility in rabbits (Oryctolagus cuniculus) using non-invasive imaging methods, such as radiographic barium follow through and ultrasonographic contraction counts. Time-lapse radiographic and ultrasound examinations were performed before and after a single intramuscular dose of 5 mg kg⁻¹ butorphanol, 10 mg kg⁻¹ morphine, or 10 mg kg⁻¹ tramadol. Pyloric and duodenal contraction counts by ultrasonography and radiographic repletion scores for the stomach and caecum were analysed using a mixed linear model. No significant effect was noted on ultrasound examinations of pyloric and duodenal contractions after administration of an opioid treatment. Morphine had a significant effect on the stomach and the caecum repletion scores, whereas butorphanol had a significant effect only on the caecum repletion score. Tramadol had no significant effect on the stomach or caecum repletion scores. The present findings suggest that a single dose of 5 mg kg⁻¹ butorphanol or 10 mg kg⁻¹ morphine temporarily slows gastrointestinal transit in healthy rabbits, preventing physiological progression of the alimentary bolus without the induction of ileus. In contrast, a single dose of 10 mg kg⁻¹ tramadol has no such effects.

Evaluating Pain and Analgesia Effectiveness Following Routine Castration in Rabbits Using Behavior and Facial Expressions

Prevention of pain in rabbits is a priority for both welfare and validity of scientific data. We aimed to determine if the rabbit grimace scale (RbtGS) could be used as a viable, rapid assessment tool in two breeds of rabbit, Dutch belted (DB) and New Zealand white (NZW), following orchidectomy, as an adjunct to behavioral analysis. All animals received analgesia. Rabbits were filmed and their behavior was recorded at multiple time points pre- and post-orchidectomy. Observers then scored specific pain associated behaviors for analysis. Time matched footage was also scored using the rabbit grimace scale (RbtGS). Following surgery, rabbits showed significant increases in the duration spent displaying key pain associated behaviors at 1 and 5 h post-surgery. DB rabbits that received low dose meloxicam (0.2 mg/kg) showed significantly more pain behaviors at 1 and 5 h post-surgery compared to those administered a combination of higher dose meloxicam (0.6 mg/kg) and a lidocaine/bupivacaine local infusion. DB rabbits showed an increase in RbtGS score at both 1 and 5 h post-surgery. In the NZW rabbits, an increase in RbtGS score was only observed at 1 h post-surgery. Using behavioral analysis as the gold standard for comparison, the RbtGS was an effective means of determining when rabbits are painful following orchidectomy. Higher dose meloxicam (0.6 mg/kg) combined with local anesthetic was a more effective method of reducing pain, compared to lower dose meloxicam (0.2 mg/kg) alone.

Development of the Bristol Rabbit Pain Scale (BRPS): A multidimensional composite pain scale specific to rabbits (Oryctolagus cuniculus)

A species-specific composite pain scale is a prerequisite for adequate pain assessment. The aim of this study was to develop a multidimensional pain scale specific to rabbits (Oryctolagus cuniculus) called the Bristol Rabbit Pain Scale (BRPS). The scale was developed over five phases using a unique combination of methods: focus groups and behavioural observation. The first two phases aimed at identifying descriptors to describe a rabbit in pain, and then reducing their number, both using focus groups. A total of 72 pain descriptors were grouped under six categories (Demeanour, Posture, Facial expression, Attention to the painful area, Audible and Other) and 'No pain' descriptors were added. The third phase aimed to confirm, through video observation of rabbits, the categories and descriptors previously described, to reject those terms that were ambiguous, and identify any new descriptors that had not been included in the previous list of descriptors. This led to the rejection of the categories Audible and Attention to the painful area and of 34 descriptors. Seven new descriptors were identified. The last two phases constructed the final format of the BRPS by refining the categories, ranking the descriptors on an ordinal scale and testing the internal reliability of the scale using Cronbach's alpha test. This led to a composite pain scale of six categories (Demeanour, Posture, Locomotion, Ears, Eyes and Grooming) with four intensities of pain (0, 1, 2, and 3), a total score of 0-18, and a high Cronbach's alpha coefficient (alpha = 0.843). This BRPS fills an important gap in the field of rabbit medicine and has the potential to improve the assessment and management of pain in rabbits providing veterinary professionals with a novel multidimensional pain assessment tool. Further studies will investigate the clinical utility, validity and reliability of the BRPS.

Skull Shape Diversity in Pet Rabbits and the Applicability of Anatomical Reference Lines for Objective Interpretation of Dental Disease

Acquired dental problems are among the most frequently encountered diseases in pet rabbits. However, early symptoms are often overlooked because the affected animals first appear completely asymptomatic. Alterations from anatomical reference lines according to Böhmer and Crossley applied to standard skull X-ray images, have been shown to be indicative of tooth health problems in pet rabbits. Despite its proven usefulness, there are exceptions in which the anatomical reference lines appear not to be suitable for application. We addressed this issue by quantifying the cranial morphology of a large data set of pet rabbit patients (N = 80). The results of the morphometric analyses revealed considerable diversity in skull shape among the typical pet rabbits, but variance in only a few parameters influences the applicability of the anatomical reference lines. The most substantial parameter is the palatal angle. Specimens in which the anatomical reference lines could not be applied, have a rather large angle between the skull base and the palatal bone. We recommend to measure the palatal angle before applying the anatomical reference lines for objective interpretation of dental disease. Pet rabbits with a palatal angle larger than 18.8° are not strictly suitable for the successful application of the anatomical reference lines.

Bioavailability of subcutaneous and intramuscular administrated buprenorphine in New Zealand White rabbits

Background

Buprenorphine is one of the most used analgesics for postoperative pain in rabbits. The recommended dose in rabbits (0.01–0.05 mg/kg) is the same for intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration, despite lack of pharmacokinetic data. Five male and five female New Zealand White rabbits (mean ± SD body weight 3.1 ± 0.3 kg) were administered 0.05 mg/kg buprenorphine by the IV, IM and SC routes and 0.1 mg/kg by the SC route, in a cross-over design with two-week wash-out periods between treatments. Blood was collected before, and up to 8 h post buprenorphine injection, for determination of serum levels by UPHLC-MS/MS.

Results

The area under the time concentration curve (AUC_0-t) was lower after SC (398 ± 155 ng/mL/min) than IM (696 ± 168 ng/mL/min, p < 0.001) and IV (789 ± 189 ng/mL/min, p < 0.001) administration. The maximum serum concentration was lower after SC (2.2 ± 1.4 ng/mL) than after IM (11 ± 3.2 ng/mL) administration (p < 0.001). The bioavailability was lower after SC (50 ± 19%) than after IM (95 ± 21%) administration (p = 0.006). The elimination half-life was longer after SC (260 ± 120 min) than after IM (148 ± 26 min, p = 0.002) as well as IV (139 ± 33 min) injection (p < 0.001). An increase in the SC dose from 0.05 to 0.1 mg/kg resulted in an increase in the area under the time concentration curve of 50% in female (p = 0.022) and 165% in male rabbits (p < 0.001). The bioavailability did not change in the females (36 ± 14%, p = 0.6), whereas it increased in the males (71 ± 23%, p = 0.008).

Conclusions

The lower bioavailability of 0.05 mg/kg buprenorphine after SC administration could explain the lack of efficacy seen in clinical pain studies in rabbits, using this route. For immediate pain relief, IV or IM administration is therefore be recommended, whereas SC administration may be useful to sustain analgesic serum levels, once efficient pain relief has been achieved. The current data do not support an increase in dose to compensate for the lower SC bioavailability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-020-02618-7.

Postoperative pain behaviours in rabbits following orthopaedic surgery and effect of observer presence

Rabbits are widely used in studies focusing on pain. However, pain is undertreated in this species and one possible factor to explain this is the lack of evaluation methods. The objective of this study was to identify behaviours related to orthopaedic pain in rabbits and to evaluate the influence of the presence of an observer on these behaviours. Twenty-eight rabbits undergoing orthopaedic surgery and filmed 24 hours before surgery, and 1 hour (before rescue analgesia), 4 hours (3 hours after rescue analgesia), and 24 hours post-recovery were observed in the presence and absence of an observer. The frequency and/or duration of behaviours were compared over time and between the presence and absence of the observer using the Friedman and Wilcoxon tests respectively. Data are expressed as median and interquartile range and a significant difference was considered when p<0.05. At 1 hour post-recovery, the rabbits showed reduced activity, hopping, change posture, position in the cage, explore, and open eyes in both the presence and absence of the observer. In the absence of the observer, quadrupedal posture, interact with pinecone, and eat carrot also decreased, while wince behaviour increased. In the presence of the observer, before surgery, the rabbits were less active (Presence-280; 162-300, Absence-300; 300-300) and presented a lower duration of explore (Presence-3; 0-32, Absence-40; 4-63). Post-recovery the rabbits flinched less (Presence-0; 0-0, Absence-0; 0-1) and suspended the affected limb less (Presence-0; 0-0, Absence-0; 0-65). After rescue analgesia the rabbits put weight on and raised the affected limb less (Presence-0; 0-0, Absence-0; 0-2) and licked the affected area less (Presence-0; 0-0, Absence-0; 0-2). These findings demonstrate that the presence of the observer inhibited pain-free behaviours in the rabbits, leading to a false impression of pain, and after the surgery the rabbits masked some pain signs related to the affected area.

Fentanyl Plasma Concentrations after Application of a Transdermal Patch in Three Different Locations to Refine Postoperative Pain Management in Rabbits

Simple Summary

Fentanyl patches offer “stress free” postoperative pain management in rabbits. It has been shown that fentanyl uptake is dependent on exogenous and endogenous factors of the area where the patch is applied. The purpose of the study was to investigate three different locations (neck, inner and outer surface of the ear) to obtain reliable fentanyl plasma concentrations above those previously shown to be analgesic. The fentanyl plasma concentration was measured at several time points after patch application. In addition, the practicability of the proposed methods was evaluated. The group with application on the neck had the fastest uptake and equal to or over the analgesic plasma concentration for up to 72 h. The outer surface of the ear had slightly slower uptake and shorter analgesic duration whereas fentanyl uptake at the inner surface of the ear was insufficient to provide plasma analgesic concentration. The preparation of the neck proved to be the most laborious because of the thin and dense fur and the removal of the patch resulted in erythema. In conclusion, depending on how long potent analgesia is required, either the neck or the outer surface of the ear are suitable for patch application enabling “stress free” and reliable postoperative analgesia in rabbits.

Abstract

Transdermal patches allow a noninvasive and “stress free” analgesia in rabbits. As fentanyl uptake is dependent on exogenous and endogenous factors of the area where the patch is applied, this study investigated three different locations (neck, inner and outer surfaces of the ear) for fentanyl patch application to provide adequate and reliable fentanyl plasma concentrations above those previously shown to be analgesic. Fentanyl plasma concentration was measured at different time points (3, 6, 9, 12, 18, 24, 36, 48, 72, 96, 120 h) and rabbits were assessed for their general conditions and treatment-related side effects. Practicability of the proposed methods was evaluated. Following patch application on the neck, fentanyl plasma concentrations equal to or above the analgesic value were measured in all rabbits between 6 and 72 h. Comparable concentrations were reached between 9 and 48 h in all animals for the outer ear surface. However, for the inner ear surface, analgesic concentrations were not reached, even if practicability was considered the best for this location. Preparation of the neck skin was judged as the most cumbersome due to the clipping of the dense fur and patch removal resulted in erythema. In summary, the application of the fentanyl patch on the neck and outer ear surface allowed the reach of reliable plasma concentrations above the analgesic threshold in rabbits. When applied on the neck, fentanyl patches provided the longest duration of analgesic plasma concentrations, whereas patch application and removal were easier on the outer ear surface.

Reliability and construct validity of a composite pain scale for rabbit (CANCRS) in a clinical environment

A composite pain scale for assessing and quantifying pain in rabbits (CANCRS) has been designed merging the Rabbit Grimace Scale (RbtGS) and a scale including clinical parameters (CPS). Construct validity and inter-rater reliability were assessed for CANCRS, for RbtGS and for CPS, in order to test their potential to detect pain in a clinical setting. Rabbits (n = 116) were either hybrids or purebreds and they were independently evaluated by two raters, who could be veterinarians (V) or veterinary medicine students (S). Score intervals determined four pain classes (No pain, Discomfort, Moderate pain and Severe pain) that matched presumptive pain classes associated with some pathological conditions. A chi-square test was used to assess the construct validity of the scales by checking how frequently scale results and presumptive pain classes matched. Sixty-nine patients were evaluated by one V and one S, whereas forty-seven rabbits were assessed by two V, in order to test inter-rater reliability. An intra-class correlation coefficient (ICC) was used to test reliability of the scales, whereas Cohen’s kappa tested inter-rater agreement for each parameter of the CANCRS. Construct validity results show that CANCRS and RbtGS efficiently reveal pain (P ≤ 0.05), while CPS does not (p > 0.05). Inter-rater reliability was very good for both CANCRS and CPS (ICC 0.88 V-V, 0.94 between V-S; ICC 0.97 V-V, 0.91 V-S) and good for RbtGS (ICC 0.77 V-V, 0.88 V-S); therefore, CPS reproducibility was better between veterinarians and students than between veterinarians. Inter-rater agreement between veterinarians and veterinary medicine students was moderate to very good for all the parameters included in the CANCRS (Cohen’s kappa >0,60). In conclusion, it is possible to state that the CANCRS has construct validity and it is a reliable tool for use in clinical practice, when coping with many rabbits with morphological differences. It is easy and fast to use and enriches the RbtGS with some clinical parameters that should be monitored during any clinical examination, allowing for capture of the multidimensional aspect of pain.

Prevention of Intra-abdominal Adhesions by Electrical Stimulation

The study investigated the ability of transdermal electric stimulation to prevent the formation of intra-abdominal adhesions in the combination with Seprafilm^® (anti-adhesive agent). One hundred and twenty-eight (128) rabbits were subjected to a surgical procedure to simulate the adhesion processes. After the simulation, the animals were divided into 4 groups (32 animals each), depending on the application of the methods of prevention: (1) control group (no anti-adhesives or electro-stimulation) (CG); (2) comparison group (applications of Seprafilm^®) (SF); (3) comparison group 2 (transdermal electric stimulation of the abdominal muscles) TES; (4) group (transdermal electric stimulation + Seprafilm^®) (TES + SF). We observed that the application of the Seprafilm^® alone led to a significant decrease in the adhesive process compared to the control group (CG) (p < 0.01). The adhesion process in the group underwent transdermal electrical stimulation (TES) was significantly lower compared to the Seprafilm^® group (SF) (p ≤ 0.05). The results demonstrated a significant decrease in the adhesion processes in the SF + TES group on days 1, 3, 7 and 14 in comparison with the CG group (p = 0.001), SF group (p = 0.001) and TES group (p = 0.01) group of animals. This study showed the efficacy of transdermal electrical muscle stimulation for the prevention of intra-abdominal adhesions. Moreover, the combination of Seprafilm^® anti-adhesion agent and electrical muscle stimulation resulted in the complete absence of adhesions. Our findings indicate the potential of such strategy for further clinical application.

Rabbit welfare: determining priority welfare issues for pet rabbits using a modified Delphi method

Background

Rabbits are the third most popular pet in the UK, but little research into their welfare needs has been conducted.

Methods

A modified Delphi method was used to generate expert consensus on the most important welfare issues for rabbits in the UK. The study involved 11 experts, recruited from a range of disciplines. The experts generated an initial broad list of welfare issues via an online discussion board. Two rounds of online surveys were conducted to prioritise these issues. The final round was a workshop with a subsection of experts. The experts decided that welfare issues should be ranked considering: (1) severity, (2) duration, and (3) prevalence.

Results

Experts considered that rabbits were often kept in inadequate housing, were not handled or socialised properly, were fed inappropriate diets and owners failed to vaccinate their rabbits against preventable diseases. Rabbits were thought to experience a reduced life expectancy. Lack of owner knowledge of rabbit husbandry and behaviour and, in some cases, also lack of veterinary knowledge, contributed to poor rabbit welfare.

Conclusions

The Delphi process resulted in consensus on the most significant welfare challenges faced by rabbits and can help guide future research and education priority decisions.