Experimental factors affecting the within- and between-individual variation of plantar foot surface temperatures in turkeys (Meleagris gallopovo) recorded with infrared thermography

Footpad dermatitis is a welfare concern in turkeys kept for meat production. In order to develop the basis for future standardized infrared thermography (IRT) protocols to screen for impaired foot health, this study investigated within- and between-individual temperature variation in two plantar sub-regions (Footpad, and the whole plantar Foot surface), and effects of cleaning procedures, in 80 turkey toms. A thermal camera (FLIR System AB) was used to collect IRT images. Feet were cleaned with water and dried with a paper towel. The minimum and maximum temperature (Tempmin and Tempmax) of Footpad and Foot in dirty and cleaned feet were determined. Sources of variation related to anatomical region, cleaning procedure and image analysis method were identified. Tempmax Foot was significantly higher than Tempmax Footpad both before (4.8 °C 95%CI (4.36, 5.19), t = 22.9, p < 0.001) and after cleaning (3.5 °C 95%CI (2.96, 4.04), t = 12.9, p < 0.001). Furthermore, Tempmax Foot (3.92 °C 95%CI (3.54, 4.3), t = 20.6, p < 0.001) and Tempmax Footpad (2.64 °C 95%CI (2.08, 3.2), t = 9.3, p < 0.001) were significantly higher before than after cleaning. Potential effects of e.g. evaporation and skin emissivity due to residual water, and shielding properties of dirt are discussed. In general, Tempmax variance differences were lower before cleaning than Tempmin variance differences. The variance differences between Tempmax and Tempmin Footpad before cleaning were lower for Tempmax (F = 3.38, p < 0.001), and Tempmax Footpad did not exhibit any significant variance differences before and after cleaning (F = 0.75, p = 0.2). Thus, it is necessary to create a strict protocol (i.e. specifically define the anatomical region of interest, take into account image analysis methods and cleaning procedures) for reducing errors of temperature measurements in future studies of turkey foot health. Specifically, the results indicate that Footpad Tempmax, regardless of cleaning procedures, represent an optimal anatomical region and analysis method for future studies where severity of footpad lesions and impact on animal welfare are studied.