PS12-14. Evaluation of Infrared Thermography to Assess Body Temperature in Beef Heifers of Different Breeds and Residual Feed Intake Phenotypes During Winter.

Abstract This study evaluated infrared thermography to assess body temperature in beef heifers with divergent residual feed intake (RFI) during winter. Ninety-eight beef heifers (Angus [AN], Charolais [CH], Kinsella Composite [KC], and Hays Converter [HC]; 235 ± 18.1, 225 ± 18.2, 246 ± 19.5, and 228 ± 17.5 kg body weight, respectively; 8 ± 1 mo of age) were managed in a drylot for 86 d, and fat-corrected RFI was calculated. Heifers were classified as more (LOW-RFI = −0.43 ± 0.308, −0.36 ± 0.307, −0.48 ± 0.386, and −0.54 ± 0.356 kg DM/d; n = 13, 15, 14, and 12 for AN, CH, KC, and HC, respectively) or less efficient (HIGH-RFI = 0.43 ± 0.254, 0.67 ± 0.218, 0.56 ± 0.385, and 0.59 ± 0.348 kg DM/d; n = 13, 8, 12, and 11, respectively). Weather was recorded daily, and infrared images of the frontal bone, eye, nasal bone, snout, cheek, flank, and ventral tail were collected every 17 ± 6 d using FLIR E8 PRO and analyzed using a linear mixed model with RFI, day, and interaction as fixed effects and animal as a random effect (SAS 9.4). Mean air temperature was -23, -11, -12, 3, -27, and 6 °C on d 0, 16, 30, 44, 58, and 85, respectively. Eye temperatures were greater in LOW- vs. HIGH-RFI KC but lower in LOW- vs. HIGH-RFI CH (P < 0.01). Snout temperatures were lower in LOW- vs. HIGH-RFI KC (P = 0.009), but greater in nasal bone in LOW- vs. HIGH-RFI AN (P = 0.03). Tendencies indicated lower snout, ventral tail, and nasal bone temperatures in LOW-RFI AN and CH vs. HIGH-RFI (P < 0.09). Day affected all body regions across breeds (P < 0.01). RFI × day interactions indicated that thermal responses varied with environmental conditions: a higher cheek temperature was found in HIGH-RFI AN at warmest sampling but was lower at coldest (P = 0.02); flank temperature was higher in LOW-RFI than HIGH-RFI CH at − 23 °C (P = 0.03), and eye temperature was higher in LOW-RFI than HIGH-RFI KC at − 12 and −27 °C (P < 0.001). Frontal bone temperature was higher in LOW- vs HIGH-RFI KC at 3 and 6 °C (P = 0.02), while nasal bone increased with warmer air (6 vs. -27 °C) in LOW-RFI HC (P < 0.001). A tendency for a RFI × day interaction was observed in HC for frontal bone and cheek, with higher temperatures in LOW- than HIGH-RFI at 3 and −12 °C (P < 0.09). Infrared thermography detected RFI-related temperature differences across breeds and winter conditions. However, thermal responses varied by region and breed, limiting standalone reliability. Thermography may support feed efficiency classification but requires further validation.