Body weight affects behavioural indication of thermal nociceptive threshold in adult domestic cats (Felis catus)

Abstract

a b s t r a c tCarbon dioxide (CO 2 ) thermal lasers have previously been validated for the assessment of nociception in cats. This experiment sought to assess the potential impact of factors associated with age, sex, body weight and sterilisation upon nociceptive threshold as measured by latency to display a behavioural response. Cats (N = 113) were exposed to a CO2 thermal laser three times during a 45-60 min test period depending upon the interval between tests. A minimum of 15 min elapsed between consecutive tests on any one individual. Time to display either a skin twitch or withdrawal was measured. Intra-class correlations showed the three measurements to be repeatable across tests for any given cat (ICC = 0.482; P < 0.001). Males had a significantly longer mean latency to respond than females (14.83 s and 12.59 s respectively; P = 0.028). Analyses of co-variance 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 ttest 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 particularly as it relates to subcutaneous fat deposition and skin temperature. It is concluded that, for cats, the body weight of the subject should be standardised or included in any analyses for assessment of nociception. Inclusion of body weight data in analyses may also prove useful when using a CO2 laser protocol in other species.

Assessment of a carbon dioxide laser for the measurement of thermal nociceptive thresholds following intramuscular administration of analgesic drugs in pain-free female cats

“…Although aberrant results often occur, it is possible that the protracted length of the experimental period in this study in comparison with those in earlier studies (Farnworth et al. ,b) may have increased the tendency for non‐response.…”

“…In a previous study using cats, all responses to 500 mW thermal stimulation occurred in <60 seconds (Farnworth et al. ) and therefore 60 seconds was set as the maximum duration for exposure to the thermal stimulus.…”

“…Approximately 24 hours prior to the commencement of testing, each cat's fur was clipped to skin level on both sides of the thorax as per the technique outlined in Farnworth et al. (). The cats were not removed from their colony cages during this procedure.…”

“…rising to its feet or significantly easing its body) or exhibiting the panniculus reflex, or until the pre‐determined cut‐off time of 60 seconds was reached (Farnworth et al. ). The laser was turned off immediately following either of these behavioural responses.…”

“…) and inter‐individual variability (Farnworth et al. ). It has not yet been used to explore the effects of pharmacological manipulation of nociceptive thresholds.…”