Thermographic monitoring of skin surface temperature associated with hot-iron disbudding in calves

The goal of this study was to determine the skin surface temperatures of the head using thermography in 28 German Holstein heifer calves at the time of hot iron disbudding. Calves were divided into group 1 (hot-iron disbudding, n = 14) and 2 (sham disbudding, n = 14). Thermographic measurements were made at eight locations of the head (area surrounding both horn buds, both horn buds, muzzle, mucous membranes of the muzzle, both eyes) at nine time points (- 60 min (basal value), time of disbudding, 5, 30, 60, 90, 120, 240 and 480 min after disbudding) using a high-end thermographic camera (TherrnoPro TP8, Firma DIAS Infrared GmbH). The rectal temperature was measured 60 min before and 5, 240 and 480 min after disbudding. The statistical software SAS version 9.4 was used for analysis. Skin surface temperatures and rectal temperature correlated at several locations (r(p) >= 0.45; p <= 0.05). The maximum temperature (approx. 67 degrees C) was measured at the horn buds immediately after the hot-iron procedure. By five and 30 min after hot-iron disbudding, the temperature of the horn buds had decreased by up to 50%, whereas the temperatures at the other locations had increased significantly (p < 0.01) in both groups compared with the basal values. Measurements at 60, 90 and 120 min after the procedure both groups showed a continuous temperature increase (vicinity of both horn buds, both eyes and at the muzzle and associated mucous membranes) or a temperature plateau (both horn buds). The temperature returned to basal values at all locations (excl. muzzle and associated mucous membranes) between 4 and 8 hours after the procedure. The similarities between the temperature patterns observed in the present study and published blood cortisol concentrations in calves undergoing hot iron disbudding suggest that temperature increases reflect a perioperative stress response. Further studies are necessary to evaluate whether thermography of the head could serve as a proxy for the non-invasive evaluation of pain and stress in calves.