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Effects of Room Temperature on Ear Surface Temperature of Late-Finishing Pigs
Thermal imaging can be used to monitor the thermal comfort of pigs. The objective was to establish the effect of room temperature on skin surface temperatures using thermal imaging of pigs kept under conditions similar to commercial practice. The study was carried out as a RCBD; with 2 room temperature treatments: 1) Thermoneutral (TN constant 18°C); and 2) Hot (30°C from 0800-1900; 20°C from 2000-0700). There were 4 rooms of finishing pigs (2 on each temperature treatment). Rooms had fully-slatted concrete floors and there were 8 pens of 10 pigs in each room; floor space was 0.67 m2/pig. Images were taken on 20 randomly selected pigs from each room every 2 wk over an 8-wk period during which mean BW increased from 83.8 ± 11.21 to 129.1 ± 11.42 kg. Images were taken of the ear using 2 cameras (FLIR E6 and IRISYS IRI4010; sensitivity of 0.06 °C and 0.15 °C, respectively; resolution of 160 x 120 pixels). Emissivity on all images was set at 0.98. Images from each camera were processed with the respective program (FLIR Tools, IRISYS 4000 Series Imager) Surface temperature was measured at 5 points along the centerline of the ear: where the ear joins the head, near the tip of the ear, and 3 points equidistant between these 2 points. All observations for both cameras across the study period were averaged by temperature treatment for each point and an unpaired t-test was used to compare the effects of room temperature. The average ear temperature across all 5 points for the Hot and TN treatments was 26.5 ± 3.3 °C, and 23.0 ± 5.6 °C, respectively (P = 0.11). Ear temperature was greater (P < 0.05) for the Hot than TN treatment the tip of the ear (23.96 °C and 18.52 °C, respectively) but not at the other measurement points (P > 0.05). The difference in ear temperature between the point closest to the head and the tip of the ear was greater for the TN than the Hot treatment (4.12 and 8.11 °C, respectively; P < 0.0001). These results suggest that high environmental temperatures increase the surface temperature at the extremity of the ear due to increased vasodilation, and that the difference in temperature from the base to the tip of the ear may be the most appropriate measurement to assess the thermal comfort of the animal.
Keywords: Thermal imaging, heat stress, vasodilation