Environmental factors affecting measurement of bovine scrotal surface temperature with infrared thermography

The objective was to determine the effect of time of day (diurnal variation), interval after feeding, prolonged recumbency, moisture on the scrotum, and ambient temperature on scrotal surface temperature (SST) in bulls as measured by infrared thermography. There was no significant effect of diurnal variation on SST. Within 30 min after the start of feeding, SST at the bottom of the testes and average SST increased, and slowly declined thereafter. In bulls that were lying down for at least 1 h, SST remained relatively constant after rising at an ambient temperature of 15°C, but increased after rising at ambient temperatures of 5 and 25°C. Ambient temperature had a large effect on bottom SST, a small effect on top SST and an intermediate effect on average SST. The SST gradient (difference between top and bottom SST) was greatest at 5°C and least at 25°C. When ambient temperatures changed rapidly, there was an apparent overcompensation in SST (measured 3 h after ambient temperature stabilisation), followed by a normalisation of the temperature (measured 24 h after temperature stabilisation). Moisture on the scrotum decreased SST and following drying returned to normal in approximately 30 min. Therefore, for representative SST measurement, scrotal infrared thermography can be performed at any time of the day, but should not be done within several hours of feeding or until 1 h after rising, and the scrotum should be dry. Measurement of SST can be conducted over a wide range of ambient temperatures, although abrupt changes in ambient temperature may result in artifacts due to overcompensation.