Answer: Myth (according to one recent study…..)
Digital thermometers provide a quick, easy means to take a horse’s temperature – whether because there might be reason to believe that the horse is sick or because we need to prove that the horse is healthy. The question is whether they are as accurate as a conventional thermometer.
At Massey University, a group of researchers set out to answer this very question. They compared (4) different brands of digital thermometers with (2) brands of mercury thermometers and (1) ethanol thermometer. In the first part of the study, each thermometer was submerged in temperature controlled water 4 times, with an average values recorded. A mercury thermometer of a brand used most often by the group was used as a reference. (5) of the thermometers produced values within .07 degrees C of the reference, with (2) of the digital thermometers registering lower average temps (one by .2 degrees, the other by .1 degree) In the second part of the study, the thermometers were tested on cattle, sheep and horses. A reference body temp for the horse was obtained and it was found that on average (2) digital thermometers registered lower temps and the ethanol thermometer registered higher temp. Overall, the temperature range was from 97.34-102.02 degree F. The digital thermometer that produced the fastest result also had reading that varied furthest from average. The researchers felt that perhaps the size and shape of the thermometer may affect its ability to contact the rectal wall and therefore, to, to produce a more accurate reading. Recognizing that, in the face of potential sickness, a falsely low reading may mean missing a fever in that horse. They concluded by stating that closer monitoring of the accuracy of these digital thermometers needs to be undertaken as their use becomes more popular.
Scientific Article: Hine, L., Laven, R., Sahu, S. “An Analysis of the effect of thermometer type and make on rectal temperature measurements of cattle, horses and sheep,” NZ Vet J Sept. 29, 2014, 1-8.
Companion Article: Barakat, C. and McCluskey, M. “The Accuracy of Digital Thermometers Investigated,” EQ Medical Front, Equus, issue 451, April 2015, p.15.