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Bovine Core Body and Scrotal Temperature Measured Using Surgically Implanted Temperature Sensitive Radio-transmitters, IButtons and Infrared Thermography
An ability to continuously and remotely monitor body (BT) and scrotal temperature (ST) without adverse or behavioral interference is fundamental to any study that investigates thermoregulation of the testis. Several methods for monitoring BT exist; loggers inserted into the rectum or vagina or placed in the ear close to the tympanic membrane, implantable radio-transmitters (RT) and rumen boluses. However, with all but RT and rumen boluses, data can only be collected for a few days. Previously, ST had only been measured via thermocouples for short durations (hours) or by manual scanning of microchips. This study compared the 3 most suitable technologies available for the coincident measurement of BT and ST; temperature sensitive RTs, data logging iButtons (IB) and infrared imaging (IRI). Bundles containing RT and IB were calibrated and surgically implanted in the abdominal muscle wall and scrotum of 6 bulls for between 29 to 49 d. IBs logged every 30 min and RT pulse intervals were scanned every 15 min. Hourly IRI were taken of the body and scrotum of each bull for one 24 h period. Histology samples were obtained after castration at the conclusion of a series of heat-stress trials. IB were more reliable than the RT; all RT lost at least 11 % of data whilst 11 of the 12 IB had 100 % data recovery. Pearson correlations between IB and RT were strong for both BT (r > 0.94, P < 0.001) and ST (r > 0.80, P < 0.001). Bland-Altman plots (limits of agreement) also showed stronger agreement with BT than ST; possibly due to the temperature gradient within the scrotum. The surgical procedure produced minor inflammation and hematoma in 2 animals immediately after the surgery. On castration, scar tissue was observed at all surgical sites but active spermatogenesis was evident in 10 of the 12 testicles. As all animals had been used in additional heat stress trials, it was impossible to determine the exact pathological effect of implant surgery. No significant correlation of IRI with either IB or RT existed, although sample size was small and given that IRI measures surface temperature rather than BT, the usefulness of IRI is uncertain. IB provided a reliable, robust, and continuous BT and ST data set, and can be successfully implanted in both the abdomen and scrotum of bovines.
Keywords: Scrotal-temperature, iButton, radio-transmitter