Tympanic Membrane Temperature for Indicating Rapid Changes in Body Temperature

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Abstract
Sections of bovine heads were made to determine the anatomy of the ear canal and its relationship to 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 the mature bovine the canal [base of the outer ear to the turn] measured 10-13 cm in length and 0.6 cm in diameter. Semiflexible thermister probes were used to sense the temperature near the tympanic membrane and 20 cm probes were used in the rectum. Comparisons of the speed of response between tympanic and rectal temperature were made with ambient temperatures cycling (20-45-20 C) and constant temperature (52 C). The speed of response to an internal stimulus (introduction of ice in the rumen) was made at 42 C. Tympanic temperature responded more rapidly to both 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 temperature declined in 2-4 min., rectal temperature averaged 15 min. Thus, the tympanic membrane temperature is more suitable than rectal temperature for determining the speed of response of the bovine to both internal and external temperature changes.