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Tympanic Membrane Temperature for Indicating Rapid Changes in Body Temperature

Animal Husbandry Research Division, USDA, Beltsville, Maryland

ABSTRACT

Sections of cattle heads were made to study the ear canal and its relationship to the tympanic membrane and the hypothalamus. The ear canal extends forward and downward and tapers slightly. Approximately 0.6 cm distal to the tympanic membrane, it turns approximately 45 degrees. In mature animals, the ear canal—base of the outer ear to the 45-degree turn—measured 10–13 cm in length and 0.6 cm in diameter.

Semiflexible thermistor probes were used to sense the temperature near the tympanic membrane and 20 cm in the rectum. Comparisons of the response of tympanic membrane and rectal temperatures were made with ambient temperatures cycling (20-45-20 C) and constant (52 C). A comparison of the speed of response to an internal stimulus—introduction of ice into the rumen—was made at 42 C. Tympanic temperature responded more rapidly to rising and declining ambient temperatures (rising tympanic 2-4 min, rectal 20 min; declining tympanic 2 min, rectal 6 min). Following the internal stimulus, tympanic declined in 2-4 min, whereas rectal averaged 15 min.

It appears that temperature sensed at the tympanic membrane is move suitable than rectal temperature for determining the speed of response of cattle to both internal and external temperature changes.