Thermographic application in pigs: relationship between surface and core temperature

Several studies report that body temperature in pigs is a valid indicator for welfare assessment. However, body temperature is difficult to be measured under farm conditions, as the accepted methods for measuring core temperature need handling and restraining of animals. Infrared thermography (IT) has been used in several species as a non-invasive technique to estimate the body temperature by detecting infrared radiation emitted by any body. The aim of this study was to assess the relationship between surface temperatures estimated by IT and core temperature in pigs. Eye temperature was measured in 13 pigs twice (36 and 265 days old). The experiment was performed in the facilities of Bologna University unit with a room temperature of 27°C and 20°C. Thermal images of the eye of each animal were recorded with a thermal imaging camera (Nec Avio TVS500). In order to validate IT data, rectal temperatures were measured using a calibrated digital thermometer. During the measurements, the animals were not manually restrained. Frequency distributions and Pearson correlation between the core and surface temperatures of the pigs were calculated. Data were normally distributed: the average rectal temperature was 38.9±0.3°C (MIN=38.4°C; MAX=39.5°C) and the average results of the eye temperature were 36.1±0.9°C (MIN=34.8; MAX=37.7°C). Measurements showed that the mean eye temperatures of the pigs estimated by IT were significantly correlated (r=0.731, P<0.001) with rectal temperature. Based on these results, the IT might be a useful non-contact method to measure the temperature of pig under farm conditions.