| dc.description.abstract | This thesis begins by exploring current knowledge around the domestic cat population
and gonadectomy as well as pain assessment tools and pain alleviation for cats. It
identifies a number of areas where knowledge is either absent or in need of updating
and limitations in tools for the assessment of pain in cats. It therefore proposes the
undertaking of the projects which can be found in the subsequent chapters.
Chapters two and three compared the attitudes and practices of veterinarians in New
Zealand, Australia and the United Kingdom (UK) around pre-pubertal gonadectomy
and provision of analgesia for cats. This used an electronic questionnaire which
received 717 responses. Most respondents believed pre-pubertal gonadectomy was
either entirely or ‘sometimes’ desirable (556/621). Age of patient at gonadectomy was
significantly affected by country surveyed and respondents’ provision or nonprovision
of services for pounds. Post hoc Tukey HSD analysis indicated the mean
age of both spaying and castration (both 4.3 months) in the UK was significantly
different from both Australia (spaying: 3.4 months, castration: 3.2 months) and New
Zealand (spaying: 3.4 months, castration: 3.2 months) (all p < 0.001). Mean ages at
spaying and castration were also significantly different (p=0.008; p=0.019
respectively) for non-providers (spaying: 3.9 months, castration: 3.8 months) of
services to pounds when compared to providers (spaying and castration: both 3.6
months).
With respect to the use of analgesics there has been a substantial increase in provision
of analgesia to cats undergoing gonadectomy when compared to the early literature.
There were significant differences in prevalence of analgesia provision prior to and
following spaying and castration (both p < 0.001). There were also significant postoperative
and post-discharge differences in provision of analgesia for castration, as
compared to spaying (both p < 0.001), and a similar effect was seen pre/intraoperatively
(p = 0.002).
Significant effects amongst countries and between genders relative to the desirability
of pre-pubertal gonadectomy were identified. Respondents from the UK were more
likely to answer ‘no’ (p=0.004) or ‘sometimes’ (p=0.05) as compared to those from
New Zealand or Australia. Females were more likely to respond with ‘sometimes’ as
opposed to ‘yes’ than males. Reasons for considering pre-pubertal gonadectomy
desirable or sometimes desirable focussed on reducing unwanted pregnancies and
improving population control, as well as improving rates of adoption, owner
compliance and cat behaviour and health. Post-operative provision of analgesia
following both castration (p < 0.001) and spaying (p < 0.001) also differed amongst
countries of practice. Veterinarians in Australia and New Zealand were more likely to
provide post-operative analgesia than those from the UK. Veterinarians from the UK
more commonly used
non-steroidal anti-inflammatory drugs (NSAID) in the pre/intraoperative
phase (P < 0.001) than veterinarians from either New Zealand or Australia.
Differences in attitudes towards pre-pubertal gonadectomy amongst countries may
relate to the specific Veterinary Association’s guidelines or possibly differences in
social discourse which affect perception of cats. There is substantial overlap between
the reported minimum age of gonadectomy and the age at which cats can enter early
puberty, allowing a window for unintentional pregnancy when pre-pubertal
gonadectomy does not occur. The differences in use of analgesics amongst the UK,
Australia and New Zealand may reflect differing professional considerations of the
risks associated with the use of NSAID. In the interests of animal welfare, pain relief
should perhaps be provided or offered more frequently for owner administration.
Chapters four through six explored the value of a thermal carbon dioxide (CO2) laser
for the assessment of nociceptive thresholds in cats. To begin repeatabilites were
established based on individual responses to three thermal tests on the same day and
across 4 consecutive days. A total of 12 thermal tests were conducted on 16 adult cats
(50% male). A non-thermal helium aiming laser was used as a control to ensure the
animals were responding to the thermal component of the device. All thermal tests
elicited a behavioural response 97% of which were a skin twitch known as the
panniculus reflex. No control tests resulted in this reflex behaviour. There was no
evidence that cats became sensitised or habituated to the low power thermal stimulus
on any given day (p=0.426) or across days (p=0.115). There was also no difference in
latency to respond between males and females (p=0.094), although there was a
significant day of testing and sex interation (p=0.042). Significant intra-class
correlations (ICC) demonstrated that individual responses were repeatable over days 1
to 3 (all p<0.05) but not over day 4 (p=0.096). A significant intra-class correlation
was also evident across all days when data were combined (p<0.0001).
Significant repeatabilities in the first laser-based experiment were low ranging from
0.241 to 0.414 therefore a larger sample was used (n=113) to establish any other
factors, including age or sex effects, that impacted upon thermal sensitivity. In this
next phase cats were exposed to a more powerful (500mW) CO2 thermal laser three
times during a 45-60 min test period with a minimum of 15 min elapsed between
consecutive tests on any one individual. Again time to display a behavioural response
was repeatable across tests for any given cat (ICC=0.482; p<0.001). Analyses of covariance
established that the body weight of females significantly affected response
threshold (p=0.013) but for males this effect was marginal (p=0.058). All other factors
included in the analyses were non-significant. A post hoc t-test for males and females
with overlapping body weights found no significant differences between the sexes
(p=0.721). The precise reason for the effect of body weight on latency to respond is
unknown and further exploration is needed.
Finally the CO2 laser’s ability to assess analgesia in pain-free cats was explored. Sixty
healthy adult female cats were used and randomly allocated to one of six treatments 1)
saline 0.2 ml/cat; 2) morphine 0.5 mg/kg; 3) buprenorphine 20μg/kg; 4)
medetomidine 2 μg/kg; 5) tramadol 2mg/kg; 6) ketoprofen 2mg/kg. Latency to
respond to thermal stimulation was assessed prior to intramuscular injection and at 6
time periods following injection (15-30; 30-45; 45-60; 60-75; 90-105; 120-135 min).
Thermal thresholds were again assessed using time to respond behaviourally to
stimulation with a 500mW CO2 laser. Maximum latency to respond was set at 60 sec
but given that this technique was found to cause minor skin blistering in individuals
that reached the 60s exposure limit, a cut off time of <45s is recommended..
Differences in response latency for each treatment across the duration of the
experiment were assessed using a Friedman’s test. Differences between treatments at
any given time were assessed using an independent Kruskal-Wallis test. Where
significant effects were identified, pair-wise comparisons were conducted to further
explain the direction of the effect. Cats treated with morphine (p=0.045) and tramadol
(p=0.002) showed significant increases in latency to respond over the duration of the
test period. Treatment with buprenorphine also resulted in increases in latency to
respond although only at the level of a statistical trend (p=0.091). Injection of saline,
ketoprofen or medetomidine showed no significant effect on latency to respond. The
longest latency to respond after injection of morphine was achieved at 60-75 min
whilst that of buprenorphine occurred at 90-105 min.
These projects validated the CO2 laser technique for use in cats and demonstrate that it
can be used for assessment of analgesia and may be useful for differentiating amongst
analgesic treatments. This technique may provide a simpler alternative to existing
systems although further exploration is required both in terms of its sensitivity and
comparative utility (i.e. relative to other thermal threshold systems). Future possible
experiments using this technique are to be found in the discussion chapter. | en_US |
