An analysis of the effect of thermometer type and make on rectal temperature measurements of cattle, horses and sheep

AIM: To compare the variation in rectal temperature measurement by digital, mercury and ethanol thermometers in cattle, horses and sheep. METHODS: Seven different makes of thermometer (four digital, two mercury, and one ethanol; (n=27) were tested individually in a calibrated water bath to identify whether there was an effect of thermometer make on recorded temperature. In addition, rectal temperatures of four cattle, four sheep and four horses were recorded using the same thermometers, by seven persons, with each person being assigned to one thermometer make. RESULTS: In the water bath test, mean temperature was affected by thermometer make (p<0.001) and ranged from 38.0 degrees C for the Digital Large Animal thermometer to 38.3 degrees C, which was recorded by the Rapid Digital thermometer and the three makes of capillary thermometer. There was an interaction between species and make of thermometer (p<0.001). In sheep, the lowest mean temperature was recorded using the Capillary Small Animal thermometer (39.2 degrees C) and the highest using the alcohol thermometer (mean 40.4 degrees C). In cows and horses, the highest mean temperatures were recorded by the alcohol thermometer (38.6 and 38.9 degrees C, respectively), and the lowest by the Rapid Digital thermometer (37.7 and 36.3 degrees C, respectively). Over all species, the Rapid Digital (mean difference 0.89 (95% CI=0.71-1.08)degrees C) and Genia Digiflash (mean difference 0.61 (95% CI=0.42-0.81)degrees C) both recorded lower temperatures than the reference thermometer (Capillary Small Animal). The alcohol thermometer recorded higher temperatures than all other thermometers (mean difference 0.55 (95% CI=0.35-0.74)degrees C compared with reference). There were differences in variance between thermometer types (p<0.001), with the Rapid Digital having the highest (SD 1.47) and the Capillary Small Animal the lowest (SD 0.53). CONCLUSIONS: Make of thermometer can influence rectal temperature measurements. In this study, digital thermometers generally recorded lower temperatures than mercury thermometers and had the highest variance. If digital thermometers are to be recommended for use in livestock, particularly in cattle and horses, robust data are needed showing that the specific make is reliable.