Non-Invasive Biomarkers in Saliva and Eye Infrared Thermography to Assess the Stress Response of Calves during Transport

Simple Summary Animal welfare and stress response assessment need valid animal-based indicators. Saliva has gained relevance as a non-invasive biological fluid that can be used to assess cortisol levels and different parameters of oxidative stress as potential sensitive indicators for evaluating animal welfare and health. The main objective of this work was to verify whether saliva and eye infrared thermography are accurate and efficient methods that can be used to detect transport-induced stress in calves. Our results show that transport increases salivary cortisol, oxidative status parameters, and eye temperatures. Furthermore, this study proves that the saliva of calves, as well as ocular temperature, suffers significant changes in its composition during the transport process, supporting saliva and infrared thermography as effective non-invasive methodologies to accurately assess cows' stress status. Animal transport is currently a stressful procedure. Therefore, animal-based indicators are needed for reliable and non-invasive welfare assessment. Saliva is a biospecimen with potential validity for the determination of cortisol and oxidative stress, although its use to assess calf welfare during transport has never been tested. Similarly, the applicability and reliability of infrared thermography to assess temperature change during calves' transport have never been evaluated. These objectives were outlined following the known and growing need to identify non-invasive methodologies for stress assessment in bovines. This study was conducted on 20 calves of the Arouquesa autochthone breed, at about nine months of age, during their transport to slaughter. For each animal, saliva samples and thermographic images of the eye were collected at three time points: before transport, after transport, and at slaughter. The saliva was then processed to measure cortisol levels and oxidative stress parameters (reactive oxygen species, thiobarbituric acid reactive substance, carbonyls, and advanced oxidation protein products), and the images were analyzed using FLIR Tools+ software. There was an increase in cortisol concentration and oxidative stress parameters (reactive oxygen species, thiobarbituric acid reactive substance, carbonyls, and advanced oxidation protein products) in saliva after transport. An increase in eye temperature triggered by transport was also observed. The cortisol and eye temperature results at slaughter were returned to values similar to those before transport; however, the values of oxidative stress remained increased (mainly TBARS values). These non-invasive techniques seem to be reliable indicators of stress in bovine transport, and oxidative stress parameters in saliva may be a persistent marker for welfare assessment.

Automated summary

This study investigates the use of saliva and eye infrared thermography as non-invasive methods to detect transport-induced stress in calves. The results show that transport increases salivary cortisol, oxidative stress parameters, and eye temperatures, indicating that saliva and infrared thermography are effective in assessing cows' stress status.