Oral temperature of preweaning dairy heifers: Sensitivity and specificity at detecting individuals with pyrexia

Change in body temperature can be an early indicator of illness. In calves, body temperature is routinely estimated from rectal temperature measurement. Integrating oral temperature sensors into automated feeding systems might present a feasible alternative to rectal measurement for monitoring calf body temperature. Our objectives were to determine if oral temperature is useful in detecting a fever (rectal temperature ≥39.5°C) and to establish informative oral temperature ranges in dairy calves between 0 and 28 d of life. This diagnostic accuracy study was conducted at one commercial dairy farm in central New York where calves were housed in indoor group pens of 20 calves each with free access to an automated milk feeder. Female Holstein calves (n = 150) were enrolled at birth and followed through 28 d of life. Digital probe thermometers (GLA M700) were used to measure oral and rectal temperatures (10.2 and 5.1 cm probes, respectively) simultaneously at 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26 and 28 d of life. Overall mean ± SD (n = 2,081) oral temperature was 38.4°C ± 0.7 and rectal temperature was 38.8°C ± 0.6°C. There was a moderate-to-strong positive correlation (r = 0.75) between oral and rectal temperature. A receiver operating characteristic curve used to evaluate oral temperature in detecting a true fever yielded an area under the curve of 0.91, with a sensitivity of 79% and a specificity of 98% at an oral temperature threshold of ≥39.1°C, as selected by the maximum efficiency index. Our results demonstrate the capability of oral temperature to detect a fever, and that it may be useful for monitoring body temperature changes in preweaning dairy calves. A limitation of our study was that it was conducted in winter and spring with environmental temperatures ranging from -6.7°C to 17.2°C, which mainly fall below calf thermoneutral temperatures (15°C to 25°C). Future work will evaluate the associations of oral temperature with disease and inflammation.