Core and peripheral site measurement of body temperature in short wool sheep

Understanding circadian rhythms of body temperature is important for the interpretation of single body temperature measurements and the assessment of the physiological state of an animal. The ability to measure body temperature at peripheral locations may also be important in the development of minimally invasive tools for remote temperature measurement in livestock. This study aimed to investigate how well body temperature measured at peripheral sites reflected a commonly used core measurement (vaginal temperature) and the circadian rhythmicity of the body temperature of sheep with a view to practical application in extensive sheep production systems. Eleven crossbred ewes were implanted with peripheral temperature sensing microchips (LifeChip®) which were positioned transversely in the sternocleidomastoid (neck) muscle and subcutaneously under the tail. iButton® temperature loggers were placed intravaginally to record core body temperature measurements (T<i>v</i>). The body temperature measurements observed at the peripheral sites in the neck (T<i>n</i>) and tail (T<i>t</i>) differed significantly to those measured at the core site, T<i>v</i> (<i>P</i> < 0.05), with T<i>n</i> lower than T<i>v</i> and T<i>t</i> lower than both T<i>v</i> and T<i>n</i>. Similarities in circadian rhythm patterns were observed across the day between T<i>v</i>, T<i>n</i> and T<i>t</i> in repeated measures analysis, with a short period of difference between T<i>v</i> and T<i>n</i> (from 1400 to 1600 h) and a long period of difference between T<i>v</i> and T<i>t</i> (from 1000 to 2100 h) (<i>P</i> < 0.05). These results suggest that neck muscle temperature measurements may have utility in detecting circadian rhythm patterns in core temperature in sheep, but may not accurately reflect absolute core temperatures. Peripheral measures may require adjustment or correction to more accurately reflect absolute core temperature with respect to determining accurate clinical thresholds relative to the expected normal temperature for the time of day observed. Further investigation into the utility and application of peripheral measurement of body temperature is warranted.