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Harkins, J. D., Kamerling, S. G., & Church, G. (1992). Effect of competition on performance of thoroughbred racehorses. J Appl Physiol, 72(3), 836–841.
Abstract: The effect of competition and the influence of age and sex on performance were examined in a study of 18 Thoroughbred racehorses. The horses performed two solo and two competitive runs at 1,200 and 1,600 m for a total of eight runs. No group ran faster during competition, which may have been a reflection of the quality of horses used for this study and their susceptibility to stress-induced impairment of performance. Males showed no significant difference between competitive and solo run times, whereas females were consistently slower during competition. Males ran significantly faster than females in all runs. There was no difference in run times due to age, which may have been due to the high mean age (5.9 yr) of the group. The slower competitive run times may have occurred because of an earlier onset of fatigue when compared with solo runs. Plasma lactate was significantly greater for the 1,200-m competitive than for the solo runs.
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Erber, R., Wulf, M., Aurich, J., Becker-Birck, M., Rose-Meierhöfer, S., Möstl, E., et al. (2012). Physiological stress parameters in sport horse mares transferred from group housing to individual stabling. In K. Krueger (Ed.), Proceedings of the 2. International Equine Science Meeting (Vol. in press). Wald: Xenophon Publishing.
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.
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Merkies, K., Isensee, A., MacGregor, H., Koenig von Borstel, U., Tucker, A., Carson. J., et al. (2012). Influence of psychological and physiological arousal in humans on horse heart rate and behaviour. In K. Krueger (Ed.), Proceedings of the 2. International Equine Science Meeting (Vol. in press). Wald: Xenophon Publishing.
Abstract: The interaction of horses with humans is a dynamic state, but it is not clearly understood how horses perceive humans. Nervousness is transmissible from humans to horses indicated by increased horse heart rate (HR), however no studies have investigated whether horses can differentiate between humans who are physiologicallystressed (eg. after exercising) as opposed to psychologically-stressed (eg. feeling nervous/afraid). Horses (N=10) were randomly subjected to each of four treatments: 1) no human [control], 2) a calm human comfortable around horses [CALM; N=2 humans], 3) a physically-stressed human [PHYS; human exercised to reach 70% of maximum HR; N=2 humans], and 4) a psychologically-stressed human [PSYCH; human who was nervous around horses; N=14 humans]. Humans ranked themselves on a scale of 1-10 for their nervousness around horses. Both humans and horses were equipped with a HR monitor. Behavioural observations of the horses [gait, head position relative to the withers, distance from human, orientation toward human] were recorded live. Horses were allowed to wander loose in a round pen for 5 minutes of baseline recordings, at which time the human subject entered the round pen, stood in the centre and placed a blindfold over his/her eyes. The human remained in the centre of the round pen for an additional 5 minutes. Horse HR during control did not differ from when the human was present in the CALM and PSYCH treatment, and was lower during the PHYS treatment (51a vs 54a vs 55a vs 45b bpm for control, CALM, PSYCH and PHYS respectively; a,b differ p<0.0001). Over the 5 minute test period, horse HR decreased in PHYS and PSYCH (p<0.01) whereas it increased in CALM (p<0.0001). Horse HR decreased with increasing human rank of nervousness around horses (p=0.0156), and horses stood nearer to the human when they faced the human (p<0.0001) regardless of treatment. Horses moved at a faster gait in the control treatment, and their gait was slowest in the PSYCH treatment (p<0.0001), and the horse’s head position was lower in the PHYS and PSYCH treatments compared to CALM or baseline (p< 0.0001). A lower horse head position was positively correlated to a lower horse HR (p<0.0001) and negatively correlated to horse age (p<0.0001). Human HR was affected by treatment, with PHYS having the highest HR (p<0.0001). Human HR increased when the horse was facing away from the human, even though the human was blindfolded (p=0.0395). Overall, horses appear to be influenced by the physiological and psychological state of a human without any direct contact. Horses’ posture does reflect their physiological state. Understanding how horses react to human physiological and psychological states is especially important in equine-assisted activities, where the response of the horse has specific implications for the human participant.
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