A comparison of cortisol concentrations, physical parameters and the respiratory observations for primi-parous and multiparous thoroughbred mares during weaning.

Implications The aim of the study was to determine whether the stress response to the weaning process is lower in multiparous mares when compared to maiden mares. This will determine whether specific techniques need to be applied to the individual mare to suit their breeding status, in order to decrease the negative effects of weaning stress. Stress in mares during pregnancy could have adverse effects of the success of the pregnancy, hence the stress induced during the weaning process needs to be limited. Results indicate that abrupt pasture weaning does not induce a significant stress response, based on the cortisol levels observed; indicating that is a weaning method that supports good animal welfare standards.

Introduction The individual stress response has shown to have significant effects on the brood mares’ breeding ability in terms of fertility and conception (Baccus et al., 1990). The development of knowledge in this area is essential to determine that the welfare of breeding mares is not sacrificed as a result from unsuited weaning techniques causing excess stress. The hypothesis for the study is the maiden mare will display a significantly increased cortisol peak for the post weaning sample due to lack of recent exposure to the stressful process.

Material and methods Saliva samples were collected from 11 TB mares, 4 primiparous and 7 multiparous, at -4hrs, 0hrs (weaning), +4hrs, +24 hrs and +1 week (time point 1,2,3,4,5 respectively) during abrupt pasture weaning. All mares were removed on different days, but between 12noon and 1pm on their respective days. All foals were aged 5 months. The salivary sample was initially centrifuged for 15 minutes at 1500xg to allow separation of saliva and residue phases. The organic phase was then transferred using a plastic pipette into a new test tube. The cortisol was extracted from this organic phase by the use of ethyl ether. The substance was then evaporated by nitrogen stream which then left the remaining cortisol residue at the bottom of the test tube after the ether had evaporated. Extraction buffer (provided in the standard EIA kit) was then added to this residue prior to the assay procedure. Coated microplate, cortisol-HRP conjugate, TMB substrate, cortisol known standard, Extraction buffer, EIA buffer and wash buffer were provided by the commercially purchased EIA kit from Oxford Biomedical Research Inc. from the saliva samples and subsequently analysed using an ELISA to determine cortisol concentration (Moons et al., 2005). The cortisol levels for the two groups of mares were compared at the five time points using a Multivariate Analysis of Variance (MANOVA).

Results The MANOVA did not show any significant differences in salivary cortisol level between the two groups of mares or the five time points. When using Pillai’s trace, there was no significant effect of mare parity on the cortisol concentrations at the any of the five time points observed, V=0.3, F(5,5)=1.65, (ns).

Conclusion Pasture weaning does not seem to elicit a systemic physiological stress response at the time of weaning or thereafter in the broodmares, regardless of their parity. Future research should aim to investigate the effects of age and parity on cortisol levels, using a more representative sample with evenly sized groups to confirm these findings.. The current results indicate that pasture weaning is an appropriate weaning method, causing minimal, if any, welfare concerns for the mares involved in this study, and therefore this would be the recommended weaning procedure from the dams perspective in the equine breeding industry.