Is the concentration of corticosterone in egg albumen an appropriate measure of the stress response?

By Prafulla Regmi - Stresses during different stages of production are often implicated as causes of compromised welfare in poultry. Quantification of stress parameters, primarily corticosterone, has become commonplace in poultry research as an indicator of animal welfare. Traditionally researchers have measured corticosterone concentration in blood plasma. However, the act of blood collection is invasive and involves proper restraining of the bird which is often enough to initiate the acute stress response by itself and will confound the measure of corticosterone concentrations. This has led to the use of a number of non-invasive methods to measure corticosterone concentrations in poultry research.
 
Corticosterone concentration in egg albumen has been frequently used as an indicator of stress and welfare in laying hens in different housing systems. Commercially available ELISA kits have been used for direct immunoassay of egg albumen corticosterone levels. However, the reliability of such techniques has not been tested against gold standards such as high-pressure liquid chromatography (HPLC) and/or mass spectrometry (MS). To address this issue, researchers from Australia used eggs from brown egg-type laying hens that were housed in conventional cages to conduct HPLC coupled with MS to measure corticosterone levels in the albumen.
 
They found a very low concentration of egg-albumen corticosterone (0.029-0.091 ng/g), which was barely above the threshold of detectability. Although only 12 eggs were used in the experiment, these results indicate that the ELISA assay commonly used to measure egg corticosterone levels is greatly overestimated. Interestingly, the authors reported that cortisol levels in egg albumen (0.24-1.60 ng/g) was far greater than corticosterone levels.
 
These findings are quite important and highlights the fact that any physiological measure should be validated before being used as indicators of poultry welfare. Additionally, physiological measures of stress should be complemented with indicators of health and behavior to comprehensively assess welfare. Finally, physiological roles of cortisol during chicken stress responses should be explored as a potential marker of stress.
 
The full paper can be found here.
Caulfield, M. P., & Padula, M. P. (2020). HPLC MS-MS Analysis Shows Measurement of Corticosterone in Egg Albumen Is Not a Valid Indicator of Chicken Welfare. Animals 10(5), 821. https://doi.org/10.3390/ani10050821 

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