Abstract:
BACKGROUND: 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.
RESULTS: 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.
CONCLUSIONS : 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.
