*3.1. Thermal System*

### 3.1.1. Evaluation of Remote Control (Table 1)

The IR control was successful in all the species, and there were few incidents where contact was lost. The signal was used either by pointing the transmitter directly at the control unit on the animal or by intentionally reflecting the signal o ff a reflective surface. The only materials that proved inadequate for reflection were rough high wooden roofing in a barn or horse bedding on the ground. Inclusion of the aerial on the animal and a fixed transmitter position prevented loss of contact through human error in misdirecting the signal and facilitated separation of the tester from the animal. Low ambient temperature did not a ffect the unit's function, except that more power (i.e., a fully charged battery) was required to heat to threshold temperature from a lower starting point.


**Table 1.** Skin temperature (◦C) (range) and thermal nociceptive threshold (◦C) (TT) (mean ± SD (range)) recorded with a remote controlled system during training in cats, dogs, sheep, horses and camels.

Probe: old style [8], new style [17]. Cut-out (c/o): temperature set to cease heating automatically when no response is detected. Opioid treatment: butorphanol, methadone, buprenorphine or methadone/sedative combinations as detailed in the text.

### 3.1.2. Comparison with Wired System

In the four DEV1a cats, mean ± SD baseline with the remote system was 43.6 ± 2.1 ◦C and with the wired system 42.0 ± 1.7 ◦C. Excursions (TT – skin temperature) in four cats (DEV1a) were 5.0 ± 1.1, 2.8 ± 0.9, 3.0 ± 0.5, 4.0 ± 2.1 ◦C (remote) and 4.4 ± 1.3, 3.4 ± 1.3, 5.3 ± 1.3, 6.1 ± 1.0 ◦C (wired). Excursions measured with both systems were not statistically di fferent. Peak excursions in two cats were >13.1 ◦C (reached cut-out) 10–105 min after butorphanol, similar to previous data from opioid-treated cats using the original system [23,24].

In group DEV1a cats (*n* = 4), the skin temperature was always higher when recorded by the remote system compared with the wired (wired 36.8 ± 0.6 and remote 39.4 ± 1.5, *p* < 0.001). Remote TT was higher than wired in only one cat, and the mean difference was small although significantly different (wired 42.0 ± 1.7 and remote 43.6 ± 2.1, *p* < 0.01). However, the excursions recorded with the remote system were smaller than with the wired (wired 5.2 ± 1.4 and remote 4.3 ± 2.0, *p* < 0.05). The TT in all Group DEV1b (*n* = 4) cats increased after opioid treatment. Peak excursions ranged between 16.1 and 18.2 ◦C, which is similar to published data (Table 2).

**Table 2.** Thermal thresholds (TTs) in group DEV1b cats. Peak excursions (skin–TT difference) after treatment with intramuscular (IM) butorphanol 0.4 mg/kg or sub-lingual (SL) buprenorphine 20 μg/kg. Published approximate mean peak delta T data after buprenorphine and butorphanol included for comparison.


The historical data from CDEV1 cats (*n* = 12) using the wired system [6] and CDEV2 cats (*n* = 12) using the wireless system [18] showed that mean skin temperature in CDEV1 cats was always 1–2 ◦C lower than in CDEV2 cats. The TT in both groups increased significantly after buprenorphine treatment, remaining higher than pretreatment from 60 to 240 min in CDEV1 and from 30 to 300 min in CDEV2. The TTs were similar except 1–2 h after treatment, when CDEV2 TTs were higher.
