Effect of different head–neck positions on physical and psychological stress parameters in the ridden horse

Different head–neck positions (HNPs) are used in equestrian sports and are regarded as desirable for training and competition by riders, judges and trainers. Even though some studies have been indicative of hyperflexion having negative effects on horses, this unnatural position is frequently used. In the present study, the influence of different HNPs on physical and psychological stress parameters in the ridden horse was investigated. Heart rate (HR), heart rate variability (HRV) and blood cortisol levels were measured in 18 horses. Low frequency (LF) and high frequency (HF) are power components in the frequency domain measurement of HRV which show the activity of the sympathetic and parasympathetic nervous system. Values were recorded at rest, while riding with a working HNP and while riding with hyperflexion of the horse's head, neck and poll. In addition, rideability and behaviour during the different investigation stages were evaluated by the rider and by an observer. Neither the HR nor the HRV showed a significant difference between working HNP (HR = 105 ± 22/min; LF/HF = 3.89 ± 5.68; LF = 37.28 ± 10.77%) and hyperflexion (HR = 110 ± 18; LF/HF = 1.94 ± 2.21; LF = 38.39 ± 13.01%). Blood cortisol levels revealed a significant increase comparing working HNP (158 ± 60 nm ) and hyperflexion (176 ± 64 nm , p = 0.01). The evaluation of rider and observer resulted in clear changes of rideability and behavioural changes for the worse in all parameters collected between a working HNP and hyperflexion. In conclusion, changes of the cortisol blood level as a physical parameter led to the assumption that hyperflexion of head, neck and poll effects a stress reaction in the horse, and observation of the behaviour illustrates adverse effects on the well‐being of horses during hyperflexion.     

Cortisol release and heart rate variability in sport horses participating in equestrian competitions

Equestrian competitions require both physical activity and mental adaptation in horses. Cortisol, heart rate, and heart rate variability (HRV) are accepted stress parameters and, in this study, have been determined in horses (n = 13) participating in equestrian competitions for up to 3 consecutive days. Participation in competitions caused an increase in salivary cortisol concentrations (e.g., on day 1 from 1.0 ± 0.2 before to 2.2 ± 0.4 ng/mL after the competition, days 1 and 2: P < 0.001, day 3: P < 0.05) and an increase in heart rate (days 1 and 2: P < 0.001, day 3: P = 0.01). A consistent decrease in HRV occurred only in response to the final competition on day 3 (P < 0.01). When horses competing in dressage and show jumping were compared, cortisol release and HRV did not differ between groups, but after the competition, heart rate was lower in dressage than in show jumping horses (P < 0.05). Heart rate increased not only during the actual competition but already when horses were prepared in their stables (e.g., day 1: ?60 minutes, 38.6 ± 2; ?5 minutes, 77 ± 7; competition, 81 ± 10 beats per minute; P < 0.01). In conclusion, participation in equestrian competitions caused an increase in cortisol release and heart rate and a decrease in HRV variables. However, competitions were not a major stressor compared with other anthropogenic challenges such as transport, to which horses are exposed regularly.     

Cortisol release,heart rate,and heart rate variability in transport-naive horses during repeated road transport

Domestic animals are often repeatedly exposed to the same anthropogenic stressors. Based on cortisol secretion and heart rate, it has been demonstrated that transport is stressful for horses, but so far, changes in this stress response with repeated road transport have not been reported. We determined salivary cortisol concentrations, fecal cortisol metabolites, cardiac beat-to-beat (RR) interval, and heart rate variability (HRV) in transport-naive horses (N = 8) transported 4 times over a standardized course of 200 km. Immunoreactive salivary cortisol concentrations always increased in response to transport (P < 0.001), but cortisol release decreased stepwise with each transport (P < 0.05). Concentrations of fecal cortisol metabolites increased from 55.1 ± 4.6 ng/g before the first transport to 161 ± 17 ng/g the morning after (P < 0.001). Subsequent transport did not cause further increases in fecal cortisol metabolites. In response to the first transport, mean RR interval decreased with loading of the horses and further with the onset of transport (1551 ± 23, 1304 ± 166, and 1101 ± 123 msec 1 d before, immediately preceeding, and after 60–90 min of transport, respectively; P < 0.05). Decreases in RR interval during subsequent transports became less pronounced (P < 0.001). Transport was associated with a short rise in the HRV variable standard deviation 2 (P < 0.001 except transport 1), indicating sympathetic activation. No consistent changes were found for other HRV variables. In conclusion, a transport-induced stress response in horses decreased with repeated transport, indicating that animals habituated to the situation, but an increased cortisol secretion remained detectable.     

Changes in cortisol release and heart rate variability in sport horses during long-distance road transport

It is widely accepted that transport is stressful for horses, but only a few studies are available involving horses that are transported regularly and are accustomed to transport. We determined salivary cortisol immunoreactivity (IR), fecal cortisol metabolites, beat-to-beat (RR) interval, and heart rate variability (HRV) in transport-experienced horses (N = 7) in response to a 2-d outbound road transport over 1370 km and 2-d return transport 8 d later. Salivary cortisol IR was low until 60 min before transport but had increased (P < 0.05) 30 min before loading. Transport caused a further marked increase (P < 0.001), but the response tended to decrease with each day of transport. Concentrations of fecal cortisol metabolites increased on the second day of both outbound and return transports and reached a maximum the following day (P < 0.001). During the first 90 min on Day 1 of outbound transport, mean RR interval decreased (P < 0.001). Standard deviations of RR interval (SDRR) decreased transiently (P < 0.01). The root mean square of successive RR differences (RMSSD) decreased at the beginning of the outbound and return transports (P < 0.01), reflecting reduced parasympathetic tone. On the first day of both outbound and return transports, a transient rise in geometric HRV variable standard deviation 2 (SD2) occurred (P < 0.01), indicating increased sympathetic activity. In conclusion, transport of experienced horses leads to increased cortisol release and changes in heart rate and HRV, which is indicative of stress. The degree of these changes tended to be most pronounced on the first day of both outbound and return transport.     

Comparison of heart rate and heart rate variability obtained by heart rate monitors and simultaneously recorded electrocardiogram signals in nonexercising horses

Heart rate (HR) and heart rate variability (HRV) are often determined with Polar heart rate monitors (HRMs; S810i; Polar, Kempele, Finland). The aims of this study were to compare data from horses obtained by Polar HRMs and a portable Televet electrocardiogram (ECG; 100 version 4.2.3; Kruuse, Marslev, Denmark) device and to determine appropriate recording times in horses (n = 14). Correlations were calculated and a Bland-Altman analysis was carried out to examine agreement between recording systems. For beat-to-beat (RR) interval, uncorrected and corrected data were highly correlated irrespective of the recording system and recording time (r > 0.99, P < 0.001). For HRV variables, standard deviation of RR interval and root mean square of successive RR intervals, correlations higher than 0.9 were obtained between uncorrected and corrected ECG but not Polar data. The RR interval, HR, and HRV from corrected Televet and Polar data at no time differed between the recording systems. However, with the increase in recording time, the RR interval decreased (P < 0.001). Thus, for comparisons, recording intervals of similar length should be chosen. Correlations among RR interval, HR, and HRV variables obtained by ECG and HRMs were highly significant at all recording times (r > 0.9, P < 0.001). Correlations increased with increasing recording time. Bland-Altman graphs showed a strong agreement between HRMs and ECG and mean RR intervals, HR, and HRV variables were close to identical. In conclusion, Polar HRMs are as adequate as ECG recordings in horses. Owing to a low HR in stationary horses, recording times below 2 minutes will underestimate changes in HR and HRV.     

Effects of different head–neck positions on the larynges of ridden horses

Hyperflexion, that is the strong deflection of the horse's head, poll and neck, is a prevalent training technique in equitation. Hyperflexion has come under criticism in recent years for being suspected of affecting the horses' well‐being contrary to animal welfare. The goal of the present study is a comparison between the impacts of different poll‐neck positions on findings in the upper respiratory tract of ridden horses. For this purpose, video recordings of the larynges of 14 horses were taken using an overground endoscope. The videos were recorded at rest and during three different riding phases: firstly, in a stretching posture, secondly, in a working position and, thirdly, in hyperflexion. A comparison between the analyses of the working position and hyperflexion phases revealed a significant reduction in the laryngeal opening area (p = 0.001) with a value of 8.2 ± 5.0%. Furthermore, other parameters of the larynx evaluated also showed a significant diminishment. These changes did not correlate with the age of the horses or their level of education, and they were independent of the individual anatomical conditions of the poll‐neck region. In summary, it can be stated that hyperflexion causes a considerable compression of the larynx.     

Evaluation of Dynamic Structural Disorders in the Upper Airways and Applied Rein Tension in Healthy Dressage Horses During Riding in Different Gaits and Head–Neck Positions

Flexion of the horse’s head and neck during dressage riding reduces the pharyngeal lumen with the risk of increased upper airway resistance and upper airway obstructions. According to the Fédération Equestre Internationale, hyperflexion is achieved through force, whereas the position low–deep–round is nonforced. The objectives of this study were to evaluate (1) applied rein tension and (2) dynamic structural disorders in the upper airways in dressage horses in different gaits and different head–neck positions (HNPs). Overground endoscopy (OGE) and rein tension were evaluated in 13 clinically healthy and high-performance Warmblood dressage horses while being ridden in a standardized program comprised of four different gaits (halt, walk, trot, and canter) and in four HNPs (unrestrained, competition frame, hyperflexion, and low–deep–round). All included horses were able to achieve the desired HNPs. The HNP low–deep–round showed significantly lower rein tension than competition frame (P < .001) and hyperflexion (P < .001). An association was found between dynamic structural disorders in the upper airway tract evaluated by OGE and head–neck flexion, but this association was not linked to the degree of flexion. The HNP hyperflexion was neither associated with greater rein tension nor severe dynamic structural disorders than the HNP competition frame. This study confirms that low–deep–round is a nonforced position, in contrast to hyperflexion. Further studies are needed to evaluate whether dynamic structural disorders are a result of flexion or if the degree of flexion has an impact.     

Over-flexing the horse's neck: A modern equestrian obsession?

We used an opportunistic review of photographs of different adult and juvenile horses walking, trotting, and cantering (n = 828) to compare the angle of the nasal plane relative to vertical in feral and domestic horses at liberty (n = 450) with ridden horses advertised in a popular Australian horse magazine (n = 378). We assumed that horses in advertisements were shown at, what was perceived by the vendors to be, their best. Of the ridden horses, 68% had their nasal plane behind the vertical. The mean angle of the unridden horses at walk, trot, and canter (30.7 ± 11.5; 27.3 ± 12.0; 25.5 ± 11.0) was significantly greater than those of the ridden horses (1.4 ± 14.1; ?5.1 ± ?11.1; 3.1 ± 15.4, P < 0.001). Surprisingly, unridden domestic horses showed greater angles than feral horses or domestic horses at liberty. We compared adult and juvenile horses in all 3 gaits and found no significant difference. Taken together, these findings demonstrate that the longitudinal neck flexion of the degree desirable by popular opinion in ridden horses is not a common feature of unridden horses moving naturally. Moreover, they suggest that advertised horses in our series are generally being ridden at odds with their natural carriage and contrary to the international rules of dressage (as published by the International Equestrian Federation). These findings are discussed against the backdrop of the established doctrine, which states that carrying a rider necessitates changes in longitudinal flexion, and in the context of the current debate around hyperflexion.     

Heart rate and heart rate variability in the pregnant mare and its foetus

Abortion and preterm birth of foals are major reasons for reproductive losses in the horse. Risk pregnancies require close supervision so that adequate treatment can be initiated in time. The aim of this study was to determine normal values in heart rate (HR) and heart rate variability (HRV) of the pregnant mare compared to her foetus and to detect physiological changes during ongoing gestation. In mares, the RR interval decreased from 1480±29 ms on day 270 of pregnancy to 1190±58 ms on day 330 of pregnancy (p<0.05). In contrast, foetal RR interval increased during the same time period from 611±23 ms on day 270 of gestation to 756±25 ms on day 330 of gestation (p<0.05). Concomitantly, maternal HR increased and foetal HR decreased. No further changes in RR interval occurred during the last 10 days before foaling, neither in the mare nor the foetus. In the last hours preceding parturition, maternal RR interval was lower than at all times earlier in pregnancy (average of 1037±13 ms) but did not change during this time. Maternal HRV did not change during gestation. Marked changes in HRV occurred only during the last minutes of foaling. Then, all HRV variables increased significantly (standard deviation of beat-to-beat interval: p=0.01, root mean square of successive beat-to-beat differences: p<0.01). The cardiovascular system of pregnant mares adapted to the demands of ongoing pregnancy with an increase in HR. We have no evidence that in healthy mares, pregnancy is a major stressor.     

Road Transport of Late-Pregnant Mares Advances the Onset of Foaling

Cortisol is involved in the initiation of parturition and we hypothesized that increased maternal cortisol release advances the onset of foaling. Transport is a stressor for horses and induces an increase in cortisol release. To determine stress effects on the time of foaling, late-pregnant mares were transported by road for 3 hours (n = 12) or remained in their stable as controls (n = 4). Starting on day 325 of gestation, saliva and blood samples were taken for cortisol and progestin analysis, respectively. Fetomaternal electrocardiograms were recorded repeatedly. Mares were checked for impending parturition and changes in precolostrum pH. When pH decreased to 6.5, mares were either transported or left untreated. After birth, saliva was collected repeatedly from mares and their foals and heart rate (HR) was recorded. Foals were checked for maturity and health. Gestation length was 337 ± 2 days in stressed and 336 ± 2 days in control mares. Cortisol concentration increased from 3.3 ± 0.9 to 8.4 ± 0.8 ng/mL in transported mares (P < .001) and remained constant in controls. Maternal HR and heart rate variability (HRV) did not differ between groups and neither fetal HR nor HRV changed in response to transport. In transported mares, time from precolostrum decrease to parturition was shorter (40 ± 10 hours) than the respective time in controls (134 ± 49 hours, P < .01). Neither duration of foaling nor times to first standing and suckling of foals or the postnatum increase in HR and decrease in HRV differed between groups. In conclusion, transport-induced maternal cortisol release may have advanced the onset of foaling.     

Evaluation of laryngeal function under the influence of various head and neck positions during exercise in 58 performance horses

The objective of this study was to examine laryngeal function at rest and during ridden exercise and to further analyse the impact of different head and neck positions on the laryngeal function in ridden sport horses. Fifty‐eight Warmblood horses were examined endoscopically during ridden exercise as well as during quiet breathing at rest before and after sedation. Four different head‐neck positions (unrestrained, reference, elevation and hyperflexion) were assessed during the exercise test. Laryngeal function was graded at rest and for every combination of gait and head and neck position during exercise. There was a significant correlation between the grade of laryngeal function during exercise and at rest both before (correlation coefficient = 0.794) and after (correlation coefficient = 0.741) sedation (P<0.01). No significant association was found between the grade of laryngeal function during exercise and the different head and neck positions.     

The influence of challenging objects and horse-rider matching on heart rate, heart rate variability and behavioural score in riding horses

A good horse-rider 'match' is important in the context of equine welfare. To quantify the influence of repetition and horse-rider matching on the stress of horses encountering challenging objects, 16 Warmblood horses were ridden in a test-setting on three occasions. On each occasion the horse was ridden by a different rider and was challenged by three objects (A-C). Heart rate (HR), heart rate variability (HRV) of horse and rider, and behaviour score (BS) of the horse were obtained for each object and as a total for each test. The horse-rider interaction was evaluated with each combination and assessed as 'matching' or 'mismatching', and the horses were categorised as 'compliant', 'partly-compliant' or 'non-compliant'. Horses exhibited a decreased HR (P=0.015) and a decreased BS (P=0.004) within and across different tests. 'Matching' horse-rider combinations exhibited less stress as indicated by reduced HR ('match' 69±10 vs. 'mismatch' 72±9, P=0.001) and BS ('match' 1.9±1.1 vs. 'mismatch' 3.8±1.4, P=0.017) of the horse. 'Compliant' (68±8, P<0.001) and 'partly-compliant' (71±9, P=0.002) horses had significantly lower HR than 'non-compliant' (75±9) animals. The findings of the study indicate that HR and BS measurements support a subjective 'match' diagnosis and HR measurement may be a valuable tool in assessing horse compliance.     

The effect of relaxing massage on heart rate and heart rate variability in purebred Arabian racehorses

The objective of this study was to assess the effect of relaxing massage on the heart rate (HR) and heart rate variability (HRV) in young racehorses during their first racing season. In the study, 72 Purebred Arabian racehorses were included. The study was implemented during the full race season. The horses from control and experimental groups were included in regular race training 6 days a week. The horses from the experimental group were additionally subject to the relaxing massage 3 days a week during the whole study. HR and HRV were assumed as indicators of the emotional state of the horses. The measurements were taken six times, every 4‐5 weeks. The HRV parameters were measured at rest, during grooming and saddling the horse and during warm‐up walking under a rider. The changes of the parameters throughout the season suggest that the relaxing massage may be effectively used to make the racehorses more relaxed and calm. Moreover, the horses from the experimental group had better race performance records.     

Sex differences in the response of yearling horses to handling by unfamiliar humans

In adult horses, pronounced sex differences in behavior exist, and many riders prefer male horses to mares. In the present study, we tested the hypothesis that sex differences in the response of horses to handling emerge before puberty, that is, in sexually immature animals. Warm-blooded yearling horses (6 males and 9 females) were exposed to a stationary human test (exposure to an unfamiliar person for 5 minutes) and a tolerance test (haltering and direct contact with the horse) on 5 consecutive days. The horses' behavior and heart rate were recorded. Male yearling horses displayed significantly less exploratory behavior than females during the stationary human test on days 1 and 2 (P < 0.05). Latency to halter and ease with which horses could be haltered were significantly affected by day (P < 0.05), and a significant interaction of day and sex was detected (P < 0.05; e.g., time for haltering: females, day 1: 23.8 ± 7.8 seconds [±standard error of the mean] and day 5: 21.1 ± 1.7 seconds; males, day 1: 53.6 ± 10.4 seconds and day 5: 19.4 ± 2.2 seconds). Heart rate of the horses in response to the test situations was significantly affected by day (P < 0.01) but not by sex. In conclusion, sex differences in behavior do not only exist in adult horses but are already present in young horses before puberty. When exposed to unfamiliar humans for the first time, male yearling horses display more caution than females.     

Preliminary results suggest an influence of psychological and physiological stress in humans on horse heart rate and behavior

People may involuntarily emit fear or distress signals when around horses, and interpreting how horses respond to these messages is important, particularly for human safety around horses. No studies have been done to determine if horses can differentiate between humans who are physiologically stressed (e.g., after exercising) as opposed to psychologically stressed (e.g., afraid). Horses (N = 10) loose in a round pen were randomly subjected to the presence of a stationary blindfolded human in each of 4 treatments: (1) calm human comfortable around horses (CALM), (2) physically stressed human (PHYS; exercised to 70% maximum heart rate [HR]), (3) psychologically stressed human (PSYCH; afraid of horses), or (4) no human (CONTROL). Both humans and horses were equipped with an HR monitor. Physiological and behavioral observations (gait, head position relative to the withers, distance and orientation toward human) were recorded and analyzed using a mixed model with horse and human as random effects. Increasing human fearfulness was associated with a decrease in horse HR (P = 0.0156). Horses moved at a slower gait in PSYCH (P < 0.0001), and horse head position was lower during PHYS and PSYCH compared with CALM or CONTROL (P < 0.0001). Human HR was highest in PHYS (P < 0.0001) and decreased over time in all treatments. Human HR increased when the horse was facing away (P = 0.0395). Overall, horses appear less stressed in the presence of a stationary fearful or physically stressed human than a calm person. Thus, horses in the presence of fearful humans, particularly where participants may not be comfortable around horses, should not pose any additional risk provided normal safety precautions are used.     

Stress Response of Veterinary Students to Gynaecological Examination of Horse Mares – Effects of Simulator‐Based and Animal‐Based Training

Invasive procedures in animals are challenging for veterinary students who may perceive a gynaecological examination of mares as stressful. Simulator‐based training may reduce stress. In this study, students received equine gynaecology training 4 times either on horses (group H; n = 14) or a teaching simulator (group SIM; n = 13). One day and 14 days thereafter, their diagnostic skills were tested on horses (skills tests 1 and 2). During the skills tests, the students’ stress response was analysed by heart rate, heart rate variability (HRV) parameters SDRR (standard deviation of beat‐to‐beat [RR] interval) and RMSSD (root‐mean‐square of successive RR differences), and salivary cortisol. In addition, students answered a questionnaire on their perceived stress. Sympathetic activation with increased heart rate (p < 0.001) occurred in both skills tests. In test 1, this increase was more pronounced in SIM than in H students (time × group p < 0.01). HRV decreased in students of both groups (p < 0.001). In skills test 1, this decrease was more pronounced for SIM than for H students (between groups and time × group p < 0.01 for SDRR and p < 0.05 for RMSSD). High cortisol concentrations before the skills tests may indicate an anticipatory stress response. Subjective stress perception of students was higher in skills test 1 vs 2 (p < 0.01). In skills test 2, H students felt more stressed than SIM students (p < 0.01). Self‐assessment thus differed from physiological stress parameters. In conclusion, gynaecological examination of mares evoked a moderate stress response in veterinary students, which was more evident after simulator‐based than animal‐based training.     

The effect of anesthesia and surgery on heart rate variability in dogs

Heart rate variability (HRV) may be useful for objective assessment of stress and pain in animals. The objective of this study was to describe the effect of anesthesia and surgery on HRV in dogs. We hypothesized that surgery would decrease HRV to a greater degree and for a longer duration than anesthesia alone. Four healthy male dogs (29 ± 2 kg) were instrumented for ambulatory ECG monitoring. Continuous ECG data was obtained for 1 day prior to, and 6 days following anesthesia alone (ANES) or anesthesia plus unilateral stifle arthrotomy (ANSX). The anesthetic protocol included xylazine (0.5 mg kg^–1 IM), morphine (0.5 mg kg^–1 IM), atropine (0.04 mg kg^–1 IM), thiopental (10 mg kg^–1 IV) and isoflurane in oxygen. A single dose of morphine (0.5 mg kg^–1 IM) was administered at extubation. Time domain analysis of HRV was performed on 5 minutes epochs of artefact‐ and arrhythmia‐free ECG data obtained at 12 noon and 12 midnight on each of the seven experimental days. Mean RR interval, standard deviation of normal R‐R intervals (SDNN), and the standard deviation of successive differences in RR intervals (SDSD) were compared to baseline for ANES and ANSX. Pain scores obtained during the day were also evaluated. Significance was set at p < 0.01. There were no differences between groups for any baseline data. Mean RR interval did not differ from baseline on days 1–6 in ANES or ANSX. SDNN and SDSD values at noon were not different from baseline on days 1–6 in ANES or ANSX. At midnight on days 1 and 2, SDNN was significantly decreased from baseline in ANSX, and on day 1 a significant difference between groups existed. ANSX values of SDSD at midnight were significantly decreased from baseline and ANES on day 1. Pain scores for ANSX were significantly greater than baseline on days 1–3, and different from ANES on days 1–5. These results suggest that HRV is decreased following anesthesia plus surgery, and that changes in HRV may be associated with pain.     

Heart rate variability parameters as markers of the adaptation to a sealed environment (a hypoxic normobaric chamber) in the horse

Simulated hypoxic normobaric devices have been used in human beings in order to enhance endurance capacity. These devices are sealed chambers where the athletes are supposed to stay for at least 6–8 hr daily. The current research assesses the changes in time‐domain, spectral and non‐geometrical heart rate variability (HRV) parameters in 6 horses subjected to progressive duration periods inside of a hermetically sealed chamber. It was pursued, firstly to evaluate the intensity of the stress experienced by the animals and secondly to elucidate whether the horses might require an acclimation period before implementation of hypoxic conditions. HRV parameters were monitored for 6 days: day 0 (6‐hr duration; in paddocks; basal conditions), and days 1, 2, 3, 4 and 5 (1, 2, 3, 4 and 6 hr inside the chamber every day respectively). During day 1 and during the first hours of days 2 and 3, compared to day 0, horses presented increased HR and SDHR values and decreased RR interval duration. SD1 values decreased on some hours of days 2 and 3, but differences with day 0 were not found on day 1. Increased SDNN, RMSSD, SD1 and SD2 values were observed on days 4 and 5. These results showed an activation of the sympathetic activity together with an attenuation of the parasympathetic activity during the days 1 to 3. Increased parasympathetic activity was found only during the first hours of days 4 and 5. Spectral parameters experienced minor variations, with increased LF_peak and LF% during some hours of days 4 and 5. In conclusion, at least 3 days are needed to adapt the horse to a sealed environment before starting to subject the animals to hypoxic conditions. When the horses were acclimatized, however, a minor stress was detected with they spent more than 4 hr inside of the chamber.     

Stress Response of Three-year-old Horse Mares to Changes in Husbandry System During Initial Equestrian Training

For initial training, horses are often transferred from group housing to individual boxes, which is a potential stressor. In this study, salivary cortisol concentrations, locomotion activity, and heart rate (HR) were analyzed and the HR variability (HRV) variables standard deviation of beat-to-beat interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated in 3-year-old mares (n = 8). Mares were transferred abruptly from a group stable with access to a paddock to individual boxes without a paddock and were studied from 4 days before to 5 days after changing the stable. Mares underwent routine equestrian training for young horses. On the days before mares were moved to individual boxes, cortisol concentrations showed a diurnal rhythm with values approximately 0.6 ng/ml in the morning and a decrease throughout the day. When horses were moved to individual boxes, cortisol concentrations increased to 1.8 ± 0.2 ng/ml within 30 minutes and did not return to baseline values within 6 hours (0.7 ± 0.1 ng/ml, P < .05 over time). On the following days, a diurnal rhythm was re-established but at a higher level than before the change of stable. Locomotion activity was higher when mares had access to a paddock than when kept in individual boxes. Heart rate increased for approximately 60 minutes when mares were separated from their group. In conclusion, separating young horses from their group and individual stabling are perceived as stressful.     

Heart rate and salivary cortisol concentrations in foals at birth

Heart rate (HR), HR variability (HRV) and salivary cortisol concentrations were determined in foals (n = 13) during the perinatal phase and until 5 months of age. In the fetus, HR decreased from 77 ± 3 beats/min at 120 min before birth to 60 ± 1 beats/min at 5 min before birth (P <0.01). Within 30 min of birth, HR increased to 160 ± 9 beats/min (P <0.01). Salivary cortisol concentrations immediately after birth were 11.9 ± 3.6 ng/mL and within 2 h increased to a maximum of 52.5 ± 12.3 ng/mL (P <0.01). In conclusion, increases in HR and salivary cortisol concentrations in foals are not induced during parturition, but occur immediately after birth.