Thermal Response of Laboratory Rats (Rattus norvegicus) during the Application of Six Methods of Euthanasia Assessed by Infrared Thermography

Abstract

Refinement is one of the principles aiming to promote welfare in research animals. The techniques used during an experimental protocol, including euthanasia selection, must prevent and minimize suffering. Although the current euthanasia methods applied to laboratory rodents are accepted, the controversial findings regarding the potential stress/distress they can cause is a field of research. The objective was to assess the thermal response of Wistar rats during various euthanasia methods using infrared thermography (IRT) to determine the method that prevents or diminishes the stress response and prolonged suffering. Pentobarbital (G1), CO2 (G2), decapitation (G3), isoflurane (G4), ketamine + xylazine (G5), and ketamine + CO2 (G6) were evaluated at five evaluation times with IRT to identify changes in the surface temperature of four anatomical regions: ocular (T°ocu), auricular (T°ear), interscapular (T°dor), and caudal (T°tai). Significant differences (p < 0.05) were found in G2 and G4, registering temperature increases from the administration of the drug to the cessation of respiratory rate and heart rate. Particularly, isoflurane showed a marked thermal response in T°ocu, T°ear, T°dor, and T°tai, suggesting that, in general, inhalant euthanasia methods induce stress in rats and that isoflurane might potentially cause distress, an effect that must be considered when deciding humane euthanasia methods in laboratory rodents.

Hypothalamic Neuromodulation of Hypothermia in Domestic Animals

“…These results suggest that lambs born from cold-stressed ewes might have a higher thermoregulatory capacity due to the increased BAT deposition. This is similar to what was reported by other authors, who mention that BAT deposits are particularly located at the hips and in the interscapular space [36,118,119].…”

Application of Infrared Thermography in the Rehabilitation of Patients in Veterinary Medicine

“…On the other hand, due to the factors that influence the application of IRT (e.g., the presence of hair and its length), it would be advisable to evaluate the possibility of recognizing the thermal response in different thermal windows such as the lacrimal caruncle, ocular surface or other regions sensitive to sympathetic activation [ 6 , 88 ]. Therefore, it would be important to evaluate whether the attenuation of the thermal response in the injury site is consistent with the decrease in the response of the Autonomous Nervous System, which could be an adequate indicator of the effectiveness of rehabilitation therapy [ 89 , 90 ].…”

“…Infrared thermography (IRT) is a technique that uses a specialized camera to evaluate the infrared radiation related to the temperature of a body [ 1 , 2 , 3 ]. In mammals, the infrared radiation emitted from the body is highly related to the core body temperature and the ability of consequent changes in the peripheral blood flow to increase or decrease the amount of radiated heat [ 4 , 5 , 6 ]. IRT has been used to estimate the body temperature of animals and humans through surface temperature readings [ 7 , 8 ].…”

Use of Infrared Thermography and Heart Rate Variability to Evaluate Autonomic Activity in Domestic Animals

“…A phenomenon known as stress-induced hyperthermia occurs when the BT of animals increases after the perception of a stressor [56,77]. When psychological stress is perceived by the amygdala, projections to the dorsomedial hypothalamus and the preoptic area of the hypothalamus (POA) modulate the mechanisms to increase core temperature [78].…”