Body temperature is a reliable indicator of thermal balance in cattle and can be measured at several locations e.g. tympanic, abdominal, rumen (TRUM), and rectal. Rectal temperature is the most common method used and is considered to be the gold standard' for the measurement of body temperature in cattle. However these procedures do have limitations as the animal needs to be restrained for data loggers to be inserted and because the use of data loggers within animals is restricted to short term use (≤ 10 days) or requires surgical implantation, thus limiting continuous data collection. Methods of non-invasive measurements of body temperature that are fast, efficient and reliable need to be investigated. Infrared thermography (IRT) is a non-invasive method used to visualise and determine body surface temperature. Studies investigating the relationship between body temperature and body surface temperature are limited. In this study IRT images of the head and body of feedlot cattle were collected using a thermal camera (Fluke Ti25, Fluke Corporation, Everett, WA, USA) and these were used assess the relationship between body surface temperature and TRUM.
Twelve Angus steers were housed in individual pens (10 m x 3.4 m) with access to shade for 5 d. Animals were observed at 3 h intervals for behaviour (ruminating/eating/drinking), posture (standing/laying), location (shaded/unshaded), panting score (using 0 4.5 score; where 0 is no panting, and 4.5 is open mouth, tongue extended panting) and IRT images of the head and body. Animals were observed from outside the individual pens and IRT images were taken after the completion of observations at a distance no greater than 2 m away from the animal. Mean body surface temperatures were recorded along the medial line on the head between the poll and the nose and on the transverse medial plane between the point of the shoulder (greater tubercle of humerus) and the hind limb of the animal. Rumen temperature was obtained every 10 min from each animal via orally administered boluses (Smartstock, Pawnee, OK, USA). The boluses were an active RFID transmitter which relayed a signal to a base station and then into a database (TechTrol Inc., Pawnee, OK, USA). At each transmission of TRUM the previous 12 data points (previous 120 minutes) were also downloaded, thereby minimalizing data losses. Individual 10 min TRUM data were converted to an hourly mean.
Pearson's correlation coefficient (Minitab® 16.2.0, 2010 Minitab, Inc.) were used to determine the relationship between the body surface temperature and TRUM. A strong relationship between the IRT images of the head and body (r = 0.88) was determined. However there was little relationship between the TRUM and IRT images (Figure 1) of the head (r = 0.07) and body (r = 0.06). Temperatures recorded by the IRT were generally lower than that of TRUM where mean head and body surface temperatures were 7.79 ± 0.24 °C and 7.25 ± 0.17 °C below TRUM respectively.
Figure 1: Linear trend between infrared thermography (Y axis) of the head and body against rumen temperature (X axis)
Infrared thermography may not be a suitable method in the determination of TRUM, as these data suggest that there was little relationship between the IRT of the head and body and TRUM. However further analysis is required to determine the true relationship between IRT and TRUM. Furthermore on-going work will assess the usefulness of IRT from other parts of the body, e.g. eye, as potential indicators of body temperature.
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