Salivary protein could be a useful new indicator of stress in donkeys

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Levels of a protein that can be detected in the saliva of donkeys shows promise as an indicator of transport-related stress in the animals, according to researchers.

Transportation has long been recognized as stressful for horses and donkeys.

Francesca Dai and her colleagues at the University of Milan in Italy set out to investigate whether salivary chromogranin A (CgA) concentrations could represent a new index of transportation-induced stress in donkeys.

CgA is already known as an index of stress in humans and pigs.

It is an acidic glucoprotein that is a surrogate for catecholamines, which are commonly used as a sensitive biochemical index of stress-induced activation of the sympathetic-adrenal medulla axis.

However, catecholamines are difficult to measure in saliva because of their low concentrations and rapid degradation, which is why the research team focused on CgA.

The researchers measured salivary CgA in 19 Romagnolo donkeys, comprising 15 males and four females, all kept on pasture.

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Each donkey made a trip in Northern Italy of about 64 minutes on two consecutive days. They travelled in groups of two to four, and always had familiar donkey companions with them.

Samples of saliva were gently collected 15 minutes before and 15 minutes after the two transportations for analysis.

Results showed that salivary CgA levels significantly decreased after both trips.

The researchers had expected CgA concentrations to increase.

The study team believes the physiological mechanism underlying this result may relate to the release of the peptide catestatin, which acts as an inhibitor of catecholamine release.

“However, due to the limited number of subjects involved, this hypothesis requires further investigation.”

Although CgA levels had decreased rather than increased, the results were nevertheless consistent.

“Measuring salivary CgA concentrations in donkeys may represent a promising tool for obtaining information about their stress response through a non-invasive technique that is not influenced by sampling and can be easily carried out on many animals directly in on-farm conditions,” they concluded.

The authors said that, to their knowledge, salivary levels of CgA in donkeys had not been measured before in reported studies.

The full University of Milan study team comprised Dai, Emanuela Dalla Costa, Simona Cannas, Eugenio Ugo Luigi Heinzl, Michela Minero and Silvia Michela Mazzola.

Dai, F.; Dalla Costa, E.; Cannas, S.; Heinzl, E.U.L.; Minero, M.; Mazzola, S.M. May Salivary Chromogranin A Act as a Physiological Index of Stress in Transported Donkeys? A Pilot Study. Animals 2020, 10, 972.

The study, published under a Creative Commons License, can be read here

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