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Dung testing casts spotlight on stress response in horses

dung-manure-foleyHeart rate and salivary cortisol concentrations have traditionally been used to assess stress in horses. Now, scientists in South Africa have been able to measure the byproduct of a stress hormone in the dung of horses.

The researchers say increased stress levels in horses could be detected through measuring a metabolite of the stress hormone glucocorticoid in dung.

The findings of the research, led by Martin Schulman, of the Veterinary Science Faculty at the University of Pretoria, have been published in the journal, BMC Veterinary Research.

Schulman and his colleagues used 14 pregnant thoroughbred mares, all from the same farm, for the study.

Eight of the mares were consigned to a sale, while six – the control group – remained on the farm.

The sale mares were separated from their paddock companions and grouped before their preparation for, transport to, and return from the sales venue.

Both groups were monitored by sampling at regular intervals from five days before until 14 days after the sales date to measure physiological stress in terms of changes in faecal glucocorticoid metabolite (FGM) concentrations.

In both groups, FGM levels increased post-sales before returning to pre-sales levels. Interestingly, mean FGM levels in the control mares were often significantly higher than the mares being prepared for the sales.

“Using FGM to measure physiological stress was supported by the increases observed in all mares after sales consignment, including those not consigned to the sale,” the researchers said.

The researchers also monitored the temperature of the horses each day and took periodic nasal swabs to check for EHV-1, given anecdotal evidence of EHV-1 revival being associated with the sales consignment of pregnant thoroughbred mares.

trailer-loading-oct2011One of the sales mare showed evidence of EHV-1 shedding, the researchers said.

“Monitoring FGM levels therefore represents an appropriate, minimally-invasive method for future studies to assess the contribution of physiological stress to EHV recrudescence [revival] in horses transported to sales or equestrian events,” they concluded.

The lag time between stress-related plasma hormone release and the associated appearance of the signal in faeces was about 24–48 hours, the researchers said.

Changes in FGM concentrations did not appear to be significantly influenced by changes in grass or other food intake, they noted.

The major stressful events – transport to, individual stabling and sales’ ring appearance, and return from the sales -were associated with a significant rise in FGM levels 3 days later.

“An interesting, if slightly unexpected, finding was that mares that were not consigned for sale showed significantly higher pre-sales FGM concentrations than the sales mares at nearly all time points, and a rise in FGM concentrations in the days after their herd mates had been taken to the sales, that reached statistical significance on day 10.

“Although it is difficult to separate the individual stressors that contributed to the observed response, this suggests that social disruption, in this case removal of sales mares from the settled groups and subsequent removal from visual and olfactory contact for approximately 24 hours, may be a key stressful event among settled groups of horses.

“This echoes a previous study investigating the effects of social instability on chronic stress.

“The raised FGM concentrations in non-consigned (control) mares may have been influenced by a ‘neighbour’ stress effect, given that the consigned mares remained within sight and sound of their previous group mates on all except the day of sales.

“Alternatively, or additionally, it is probable that removal of an animal from a group disrupted the social order and resulted in a potential stress-related period during which a new hierarchical equilibrium (‘pecking order’) was established,” they said.

“It is, however, less easy to interpret why the sales mares did not show higher FGM levels in the pre-sales period as a result of removal from their group and introduction into a new, albeit smaller group.”

Martin Schulman, Annet Becker, Stefanie Ganswindt, Alan Guthrie, Tom Stout, Andre Ganswindt
The effect of consignment to broodmare Sales on physiological stress measured by faecal glucocorticoid metabolites in pregnant Thoroughbred mares
BMC Veterinary Research 2014, 10:25 doi:10.1186/1746-6148-10-25 

The full study can be read here.

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