'Do You Have to Take My Pet’s Temperature Rectally?'

Ken Tudor, DVM
Published: February 17, 2015
'Do You Have to Take My Pet’s Temperature Rectally?'

Admit it. You wince and even dislike it when the veterinary nurse takes your pet’s temperature rectally. If your pet is sensitive and even aggressive when approached back there you are even more uncomfortable with the procedure. Some pets get so upset that the attempt to take a rectal temperature may result in a falsely high temperature reading.

I actually tell my staff not to take a rectal temperature if it is extremely upsetting to the pet or owner. But a pet’s body temperature is an extremely important piece of information, especially if the examination is because the pet is not feeling well. So what are the alternatives and how accurate are they?

Methods for Measuring the Temperature of Animals

There are 3 main methods for getting a pet’s body temperature:

  • Rectally with a mercury or digital thermometer
  • Axillary (pit of the front legs) with mercury or digital thermometer
  • Ear with an infra-red thermometer

The rectal temperature is considered the “gold standard” for measuring the internal core body temperature of pets. Even though fecal material, rectal inflammation, colon contractions, colon muscle tone, and physical activity (struggling to get the temperature would qualify) can affect measurements, research suggests it is still an accurate measure of core body temperature.

In general it is easy to perform a rectal temperature and requires only 30 seconds to 2 minutes, depending on the type of thermometer. Mercury and digital thermometers are reasonably priced so this is the most common method of obtaining a pet’s temperature in veterinary hospitals.

Taking an axillary temperature was commonly used in human medicine, especially with infants and younger children. This method can be used in veterinary hospital for animals that resist the rectal approach.

It was thought that the axillary temperature coincided closely with a rectal temperature. Recent research suggests that the correlation is not as close as thought. For pets with normal or low temperatures, the axillary temperature does not consistently match the rectal temperature. Even though actual temperature readings vary from axilla and rectal readings, the axillary method does not detect hyperthermia or fever in pets as well as the rectal method. If an animal is feverish the axillary temperature will pick-it up.

In humans the axillary temperature has been largely replaced by the forehead scan. Due to our pets’ fur and different sweat apparatus the forehead scan has yet to be proven useful in veterinary medicine.   

Reading the temperature of the ear canal is also used in human medicine and is increasingly being used in veterinary medicine. The infra-red technology allows the temperature to be determined in seconds. Because the reading is taken so quickly it is generally possible to get the positioning necessary for an accurate reading without too much fuss and discomfort, though I have had some dogs that do not like this method and make it somewhat more difficult than necessary. Accuracy is dependent on the infra-red beam hitting the eardrum, so if the pet won’t hold its head still it can be hard to get the scope in the right position.

There is conflicting research as to whether the ear method matches or correlates with rectal temperatures and represents a true reading of core body temperature. The veterinary grade instrument for measuring ear temperatures costs just over $200. It also requires a constant supply of disposable covers for the scope head. The company that makes the veterinary model also sells a non-professional version for around $40. Whether it has the same accuracy as the professional model, to my knowledge, has not been tested.

Because of the questionable reliability and the expense, ear temperatures may not become a universal technique in veterinary medicine. Hopefully, the technology will evolve and confidence in the readings will improve. That would certainly be much better than squeamishly suffering through the rectal procedure performed on your baby.

Which technique does your vet use?  

Dr. Ken Tudor

Image: aspen rock / Shutterstock

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