The effect of consignment to broodmare Sales on physiological stress measured by faecal glucocorticoid metabolites in pregnant Thoroughbred mares
1 Section of Reproduction, Faculty of Veterinary Science, University of Pretoria, Private Bag XO4, Onderstepoort 0110, South Africa
2 Summerhill Stud, PO Box 430, Mooi River 3300, South Africa
3 Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Private Bag XO4, Onderstepoort 0110, South Africa
4 Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Private Bag XO4, Onderstepoort 0110, South Africa
5 Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 114, 3584 CM Utrecht, The Netherlands
6 Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
BMC Veterinary Research 2014, 10:25 doi:10.1186/1746-6148-10-25Published: 17 January 2014
Validation of a method for the minimally-invasive measurement of physiological stress will help understanding of risk factors that may contribute to stress-associated events including recrudescence of Equid herpesvirus (EHV), which is anecdotally associated with sales consignment of pregnant Thoroughbred mares. In this study we compared two similar groups of late-gestation Thoroughbred broodmares on the same farm: a consigned Sales group (N = 8) and a non-consigned Control group (N = 6). The Sales mares were separated from their paddock companions and grouped prior to their preparation for, transport to, and return from the sales venue. Both groups were monitored by sampling at regular intervals from 5 days prior to until 14 days after the sales date (D0) to measure physiological stress in terms of changes in faecal glucocorticoid metabolite (FGM) concentrations, and for event-related viral recrudescence via daily body temperature measurements and periodic nasal swabs for PCR analysis for EHV-1 and -4 DNA.
In both groups, FGM levels increased post-sales before returning to pre-sales levels. Specifically, FGM concentrations in the Sales mares were significantly higher on D + 3 and D + 10 than on D-4 and D-3 (F = 12.03, P < 0.0001, Post hoc: P = 0.0003 – 0.0008) and in the Control group FGM concentrations were higher on D + 10 than D-4 (F = 5.52, P = 0.004, Post hoc: P = 0.005). Interestingly, mean FGM levels in Control mares were significantly higher at 4 of the 5 sampling points (t = 5.64 – 2.25, p = 0.0001 – 0.044). Only one (Sales) mare showed PCR evidence of EHV-1 shedding.
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. Monitoring FGM levels therefore represents an appropriate, minimally-invasive method for future studies to assess the contribution of physiological stress to EHV recrudescence in horses transported to sales or equestrian events.