Catecholamine concentrations in duck eggs are impacted by hen exposure to heat stress

Authors: Lyte, Joshua - Josh; DANIELS, KARRIE - Iowa State University; LYTE, MARK - Iowa State University; OLUWAGBENGA, ESTHER - Purdue University; FRALEY, GREGORY - Purdue University

Submitted to: Frontiers in Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2023
Publication Date: 2/6/2023
Citation: Lyte, J.M., Daniels, K.M., Lyte, M., Oluwagbenga, E.M., Fraley, G.S. 2023. Catecholamine concentrations in duck eggs are impacted by hen exposure to heat stress. Frontiers in Physiology. 14. Article 1122414. https://doi.org/10.3389/fphys.2023.1122414.
DOI: https://doi.org/10.3389/fphys.2023.1122414

Interpretive Summary: Salmonella is a foodborne bacterial pathogen that can contaminate both chicken meat and eggs. One route by which Salmonella can get into eggs is when the egg is being formed in the hen's reproductive tract. Hen stress is known to increase the chance of eggs containing Salmonella, thereby suggesting that better understanding hen stress could lead to novel ways to reduce Salmonella contamination in eggs, improving consumer food safety. Stress-related neurochemicals that form the fight or flight response, such as norepinephrine, are known to increase foodborne pathogen carriage in food animals, including poultry. Little is known whether these neurochemicals are deposited into the egg white and yolk during egg formation, especially when the hen is stressed. As such in designing novel stress-related neurochemical based strategies to control egg contamination of Salmonella, we sought to identify if these neurochemicals are present in the egg white and yolk. Also, we determined whether climate change related stressors, in this case heat stress, could increase hen deposition of neurochemicals in the egg contents. We found that stress-related neurochemicals are present in the egg contents, and that hen stress can increase these concentrations. Our findings represent the first step in designing a non-invasive measure of hen stress that could be leveraged to reduce Salmonella contamination in eggs.

Technical Abstract: Rapid ‘fight-or-flight’ responses to stress are largely orchestrated by the catecholamines. Moreover, catecholamines and catecholamine precursors are widely recognized to act as interkingdom signaling molecules between host and microbiota, as well as serve as chemotactic signals for bacterial foodborne pathogens. While albumin and yolk concentrations of glucocorticoids have received extensive attention as non-invasive indicators of hen stress, little is known regarding the impact of hen stress on in ovo catecholamine and catecholamine precursor concentrations. The aim of the present study was to determine norepinephrine and L-dopa concentrations in albumin and yolk of eggs laid by hens maintained under normal or heat stress conditions. Norepinephrine and L-dopa concentrations were also measured in oviduct tissue. Breeder ducks (30 wks/age) were kept under normal (22oC) conditions or subjected to cyclical heat stress (35oC day/29oC night) for three weeks. Eggs (n=12 per timepoint/group) were collected on a weekly basis. Hens were sacrificed at baseline or 3 wks/age for oviduct tissue collection. Albumin, yolk, and oviduct concentrations of norepinephrine and L-dopa were determined using ultra high-performance liquid chromatography with electrochemical detection. Norepinephrine and L-dopa were detected in oviduct tissue as well as egg albumin and yolk. Norepinephrine concentrations were elevated (p<0.05) in the yolk of eggs laid by the heat stress group compared to those of the control group. Norepinephrine concentrations in albumin were elevated (p<0.05) in the heat stress group compared to control group at week 2. L-dopa concentrations were not significantly affected (p>0.05) by heat stress in albumin, yolk, or oviduct tissue. Together, the present study provides the first evidence of the stress neurohormone norepinephrine in duck eggs and identifies that hen exposure to heat stress can affect in ovo norepinephrine concentrations. This data highlights the potential utility of in ovo catecholamine concentrations as non-invasive measures of hen stress, as well as warrants future research into whether hen deposition of stress-related neurochemicals into the egg could serve as a chemotactic signal in the vertical transmission of foodborne pathogens.