Abstract: Initial equestrian training and especially first mounting of a rider are stressful challenges for young horses (1). Most young horses are raised in groups but, in association with equestrian training, they are commonly transferred to individual stabling in loose boxes. Although, in most stables, visual contact with horses in adjacent boxes is possible, separation from the herd might be an additional stressor. We have studied physiological stress parameters, in 3-year-old sport horse mares (n=8), transferred from a group stable with access to a paddock to individual boxes without paddock. Once stabled in the individual boxes, mares underwent a standard training for young horses. Horses had been accustomed to lunging and tolerating a rider on their back several weeks before the study. Mares were studied from 5 days before to 5 days after changing the stable. Cortisol concentration in saliva, locomotion activity (ALT pedometers), heart rate (HR) and HR variability (RMSSD: root mean square of successive beat-to-beat intervals) were determined. We hypothesized that the change of the stable increases cortisol release and is associated with changes in HR and RMSSD and reduced locomotion. Before mares were moved to individual boxes, cortisol concentration showed a pronounced diurnal rhythm with values around 0.6 ng/ ml in the morning and a continuous decrease throughout the day. When the mares were moved to individual boxes, cortisol concentration increased to 1.8±0.2 ng/ml and did not return to baseline values within 6 h (p<0.05 over time). On subsequent days, a diurnal rhythm was re-established but shifted to a higher level than before. Locomotion activity determined by ALT pedometers was increased for some minutes only after mares has been placed in individual boxes but was only slightly higher than during the time mares spent with the group in a paddock. On days 2-5 in individual boxes, locomotion activity was reduced compared to the group stable. HR increased and the HRV variable RMSSD decreased when mares were separated. In conclusion, separating horses during initial training from their group is an additional stressor, although the stress is less pronounced than induced by other social challenges, e.g. weaning of foals (2). When stabled in individual boxes, mares move less than when kept as a group. Horses kept in a group thus appear to exercise themselves freely, such an effect is absent when the animals are kept individually.

Abstract: Domestic horses are kept in so-called “fate societies” where they have to deal with frequent mixing. Several studies have evaluated and discussed the aggression level and injury risk during the introduction of horses into new groups, but nothing is known about the endocrine responses and thus if horses experience stress during introduction.
In this study we analysed the efficiency of four approved introduction techniques and evaluated the introduction of 30 horses into 11 different groups. Horses were introduced: 1) immediately, 2) after observing the new group for several days, 3) together with an “integration horse” after several days of observation, or 4) with a mixed strategy. Aggressive as well as positive social behaviour between the introduced horses and the group members were analysed the two hours following the introduction event. In addition, we focussed on the glucocorticoid production of the newcomer horses by measuring faecal cortisol metabolites (FCM) on the day of the introduction as well as the following three days.
For the four introduction techniques we found significant differences in the horses’ aggressive and submissive behaviour as well as in their total interactions. The introduction together with an integration horse led to significantly lower levels of aggression and less total interactions than the immediate introduction of single horses.
Horses which were introduced immediately or after an observation period showed significantly elevated levels of FCM on the first, second and third day after the introduction. For horses introduced together with an integration horse FCM were already significantly higher on the day of the introduction, indicating a stressful event before the introduction itself. In contrast, FCM levels were always very low when using the mixed technique.
In sum, horses have the ability to deal with conflict when they are introduced to new group members. The introduction event itself appears not to be as stressful as previously assumed. Standing together with an “integration horse” on a separate paddock and not being able to integrate immediately into a new group appears to be stressful for the newcomer. Based on the findings of our study we suggest to introduce new horses in group management together with a new group mate, a so-called “integration horse”. This would reduce the number of total social interactions as well as the aggression level. While this technique may be stressful for the newcomer, it lowers aggressive behaviour between the introduced horse and the group members and consequently reduces injury risks.