Cortisol Concentration In Horses Research Articles

Habit Formation and the Effect of Repeated Stress Exposures on Cognitive Flexibility Learning in Horses.

Simple SummaryHorse training exposes horses to many difficult learning challenges, including tasks that run counter to their natural behaviour and research from neuroscience can be used to understand how horses respond to these learning challenges. Horses can also quickly develop habits, however if the habit is undesirable, the horse may be subjected to retraining where it must learn to suppress the unwanted behaviour and learn a new response. This is called cognitive flexibility and is underpinned by complex neural processes and can be impaired by exposure to repeated or chronic stress. We trained horses to acquire habit-like responses in one of two industry-style aversive instrumental learning scenarios (moving away from the stimulus-instinctual-IS or moving towards the stimulus-non-instinctual-NIS) and evaluated the effect of repeated stress exposures on their cognitive flexibility in a reversal task. We measured heart rate, salivary cortisol and serum brain derived neurotrophic factor to infer possible neural correlates of the learning outcomes. Horses trained in the NIS task took longer to learn task than the horses trained in the IS task, however they were quicker to learn the IS task during the reversal. There was no significant effect of the stress exposures on cognitive flexibility, however the stress did make horses more sensitive to the aversive training stimuli. These results provide guidance for trainers to adapt their practices when training tasks that are difficult for horses to learn and during retraining. In particular, even when horses have been trained to approach aversive stimuli they can quickly learn to avoid them. This has implications for retraining unwanted responses during aversive situations such as trailer loading.Horse training exposes horses to an array of cognitive and ethological challenges. Horses are routinely required to perform behaviours that are not aligned to aspects of their ethology, which may delay learning. While horses readily form habits during training, not all of these responses are considered desirable, resulting in the horse being subject to retraining. This is a form of cognitive flexibility and is critical to the extinction of habits and the learning of new responses. It is underpinned by complex neural processes which can be impaired by chronic or repeated stress. Domestic horses may be repeatedly exposed to multiples stressors. The potential contribution of stress impairments of cognitive flexibility to apparent training failures is not well understood, however research from neuroscience can be used to understand horses’ responses to training. We trained horses to acquire habit-like responses in one of two industry-style aversive instrumental learning scenarios (moving away from the stimulus-instinctual or moving towards the stimulus-non-instinctual) and evaluated the effect of repeated stress exposures on their cognitive flexibility in a reversal task. We measured heart rate as a proxy for noradrenaline release, salivary cortisol and serum Brain Derived Neurotrophic Factor (BDNF) to infer possible neural correlates of the learning outcomes. The instinctual task which aligned with innate equine escape responses to aversive stimuli was acquired significantly faster than the non-instinctual task during both learning phases, however contrary to expectations, the repeated stress exposure did not impair the reversal learning. We report a preliminary finding that serum BDNF and salivary cortisol concentrations in horses are positively correlated. The ethological salience of training tasks and cognitive flexibility learning can significantly affect learning in horses and trainers should adapt their practices where such tasks challenge innate equine behaviour.

Salivary cortisol concentrations changes in horses during daily routine

Article Details: Received: 2020-10-20 | Accepted: 2020-11-27 | Available online: 2021-01-31 https://doi.org/10.15414/afz.2021.24.mi-prap.1-4 Abstract The aim of the study was to observe the salivary concentrations of cortisol in horses during daily routine over the course of four weeks lasting experiment in three different stages of day to monitor the changing values of cortisol in horse saliva during the day. Saliva was obtained from 12 Slovak warmblood horses – 1 stallion, 6 mares and 5 geldings. In the experiment we focused purely on changes of salivary cortisol concentrations over the course of the daily routine.The results shown us multiple significant changes between individual sample collections and thus, we can state that according to our results the highest concentration of cortisol in horse saliva is in the morning and it decreases throughout the day with lowest measured concentrations being in the final sample collection of the day (at 22:00). These changes had no visible effect on horses´ organism throughout entirety of the experiment and were caused due to horses daily rhythm. Keywords: horse, cortisol, saliva, rest, daily routine References Bohak, Zs, Szabo, F, Beckers, J-F, Melo de Sousa, N, Kutasi, O., Nagy, K, Szenci, O. 2013. Monitoring the circadian rhythm of serum and salivary cortisol concentrations in the horse . Domest. Anim. Endocrinol. 45:38-42. https://doi.org/10.1016/j.domaniend.2013.04.001 Contreras-Aguilar, MD, Lamy, E, Escribano, D, Ceron, JJ, Tecles, F, Quiles, AJ, Hevia, ML. 2020. Changes in salivary analytes of horses due to circadian rhythm and season: A Pilot Study. Animals. 10(9):1486. https://doi.org/10.3390/ani10091486 Halo, M, Hollý, A, Mlynekova, E, Polyakova, L, Horný, M, Kovalcik, E. 2009. Influence feeding and training on the metabolic profil sport horses . J Cent. Eur. Agric. 10(4):411-416. Halo, M, Strapak, P, Mlynekova, E, Kovalcik, E, Horný, M. 2008. Influence stres on the training process of the horses. J. Cent. Eur. Agric. 9(1):217-224. Ille, N, von Lewinski, M, Erber, M, Wulf, M, Aurich, J, Mostl, E, Aurich, C. 2013. Effects of the level of experience of horses and their riders on cortisol release, heart rate and heart rate variability during a jumping course. Anim. Welf. 22:457-465. 10.7120/09627286.22.4.457 Irvine, CHG, Alexander, SL. 1994. Factors affecting the circadian rhythm in plasma cortisol concentrations in the horse. Domest. Anim. Endocrinol. 11(2):227-238. https://doi.org/10.1016/0739-7240(94)90030-2 Kang, O-D, Lee W-S. 2016. Changes in salivary cortisol concentration in horses during different types of exercise . Asian-Australas J Anim Sci. 29(5):747-752. 10.5713/ajas.16.0009 Kang, O-D, Yun Y-M. 2016. Influence of Horse and Rider on Stress during Horse-riding Lesson Program. Asian Australas J Anim Sci. 29(6):895-900. 10.5713/ajas.15.1068 Leal, BB, Alves, GES, Douglas, RH, Bringel, B, Young, RJ, Haddad, JPA, Viana, WS, Faleiros, RR. 2011. Cortisol circadian rhythm ratio: A simple method to detect stressed horses at higher risk of colic? Equine Vet. J. 31:188-190. https://doi.org/10.1016/j.jevs.2011.02.005 Massanyi, P, Stawarz, R, Halo, M, Formicki, G, Lukac, N, Cupka, P, Schwarcz, P, Kovacik, A, Tusimova, E, Kovacik, J. 2014. Blood concentration of copper, cadmium, zinc and lead in the horses and its relation to hematological and biochemical parameters. J. Environ. Sci. Health A. 49:973-979. 10.1080/10934529.2014.894322 Peeters, M, Sulon J, Beckers J-F, Ledoux D, Vandenheede M. 2011. Comparison between blood serum and salivary cortisol concentrations in horses using an adrenocorticotropic hormone challenge . Equine Vet J. 43(4):487-493. 10.1111/j.2042-3306.2010.00294.x Schmidt, A, Mostl, E, Wehnert, Ch, Aurich, J, Muller, J, Aurich, Ch. 2010. Corisol release and heart rate variability in horses during road transport . Hormones Behaviour. 57: 209-215. 10.1016/j.yhbeh.2009.11.003 Strzelec, K, Kankofer, M, Piertzak, S. 2011. Cortisol concentration in the saliva of horses subjected to different kinds of exercise. Act Vet. Brno. 80:101-105. 10.2754/avb201180010101 Stull, CL, Morrow, J, Aldridge, BA, Stott, JL, McGlone, JJ. 2008. Immunophysiological responses of horses to 12-hour rest during 24 hours of road transport. Vet. Rec. 162:609-614. 10.1136/vr.162.19.609 Van der Kolk, JH, Nachreiner, RF, Schott HC, Refsal KR, Zanella AJ. 2001. Salivary and plasma concentration of cortisol in normal horses and horses with Cushing´s disease. Equine Vet J. 33(2):211-213. 10.1111/j.2042-3306.2001.tb00604.x

Evaluating Stress in Riding Horses: Part One—Behavior Assessment and Serum Cortisol

Stress can impact the health and well-being of animals negatively. Behavioral and physiological changes, particularly serum cortisol, offer objective and easy-to-use methods of evaluating stress in horses. However, limited studies support a positive relationship between changes in stress-related serum cortisol concentrations and stress-related behaviors in horses. This study assessed differences in stress-related behaviors and serum cortisol concentrations in horses used in a therapeutic riding program (TRH) or university riding program (UNI). Riders were grouped by disability type (TRH) or by experience level (UNI) to determine equine stress impacts. Two trained observers evaluated equine behavior during multiple riding lessons. Behaviors were scored live and via video to assess the accuracy of live scoring. Blood samples for serum cortisol concentrations were collected before, immediately after, and 30 minutes after riding lessons. Serum cortisol concentrations decreased from before to after a riding lesson (TRH, P ≤ .01; UNI, P = .0004) and increased over the course of the study (TRH ≤ 0.0002; UNI, P ≤ .0001). All serum cortisol concentrations remained within or below normal ranges. Overall behavior scores were relatively low in horses participating in both riding programs. Similar behavior scores were observed in horses ridden by novice and experienced riders (P ≥ .1662); however, behavior scores differed in TRH horses ridden by one group of disabled riders during a riding lesson (P ≤ .0431). A relationship between stress-related behavior and cortisol concentration changes was not shown clearly, but data suggest that horses were in a low-stress environment.

Association Between Disease Severity, Heart Rate Variability (HRV) and Serum Cortisol Concentrations in Horses with Acute Abdominal Pain.

Simple SummaryAcute abdominal pain is a major cause for emergency treatment in horses and associated with a high stress level leading to an increased serum cortisol concentration. Stress can also be assessed by analyzing the heart rate variability (HRV). We investigated whether the stress level was different between horses with different causes of abdominal pain and, therefore, demanding a different treatment strategy. Heart rate, its variability in the time domain analyses, and cortisol level indicated a decrease in the stress level the day after admission and the day of discharge from the hospital in comparison to admission for both conservatively and surgically treated patients. However, such changes, over time, were not seen in horses that were euthanized during the hospitalization. Furthermore, the difference in the parameters measured between horses that were eventually euthanized and those that survived was best visible the day after admission. Therefore, we concluded that HRV can give further important information on the stress level in horses with colic and might be helpful in assessing possible outcome. However, further studies are required to assess the validity of HRV analyses in horses with colic.Heart rate variability (HRV) is a noninvasive technique to detect changes in the autonomous nervous system. It has rarely been investigated in horses with colic. Therefore, the objective was to assess the evolution of HRV parameters and cortisol concentrations in horses with colic. The 43 horses included in this study were categorized into three groups according to the treatment (1, surgical; 2, conservative; 3, euthanized). The HRV and laboratory variables were measured at admission (T1), the day after admission (T2), and at discharge (T3) and compared between groups and over time with an ANOVA with Bonferroni correction. Relationships between the HRV parameters themselves and the laboratory variables was assessed by Pearson correlation coefficients. Evolution of the heart rate (HR) over time, mean normal to normal R intervals (meanNN) and cortisol concentrations indicate a decreased sympathetic stimulation over time in group 1 and 2, in contrast to group 3. For group 3, the meanNN and HR differed significantly to group 2 at T1 and to group 1 and 2 at T2. Treatment induced a change in the HRV and cortisol response in horses managed conservatively or surgically but not in horses that required euthanasia. However, further studies are required to assess the validity of HRV analyses in horses with colic.

Temporary Relocation during Rest Periods: Relocation Stress and Other Factors Influence Hair Cortisol Concentrations in Horses.

Simple SummaryHorses are frequently transported and exposed to a new environment for sport competition or working tasks and must readapt to their original conditions after a temporary relocation. The objective of this study was to determine if a temporary relocation, and multiple factors associated with a rest period, affect the adrenal response through the analysis of hair cortisol concentrations (HCCs) in horses. Cortisol is a glucocorticoid released after the activation of the hypothalamic–pituitary–adrenal axis and its assessment is being increasingly used as a bioindicator of stress response. Results showed that changes in the daily routine of the animals, including a supposed rest period, increased the HCCs. However, the risk of using low statistical power due to the small sample size cannot be completely ruled out. The elevation in HCCs could be a consequence of the change in the horses’ environmental and routine conditions, which could, in turn, have an impact on their welfare.Horse transportation for temporary relocation during rest periods is a common and widespread practice among horse owners, either from sport competition or working tasks. This study aimed to determine the effect of a relocation period and the multiple factors associated with a rest period on hair cortisol concentrations (HCCs) in horses. Additionally, this study reports the seasonal effect on HCCs and hair growth over a year. Thirteen police horses, Pure Spanish stallions of various ages (5–13 y), were selected to participate in this study. Hair sample collection was carried out approximately every 30 d for seven months (Study 1) and a year (Study 2). Cortisol determinations were performed by enzyme immunoassay. Interestingly, Study 1 revealed that relocated horses (n = 4) exhibited elevated HCCs compared with control horses (n = 4) after the relocation period (p < 0.05). Study 2 (n = 5) showed higher HCCs during summer compared with autumn and winter, and higher hair growth rates in winter compared with the other seasons (p < 0.05). Relocated horses had higher HCCs, suggesting a change in their welfare status, probably related to the sudden change in their surrounding conditions. However, these results should be interpreted cautiously due to the low sample size used. The nature of the relationship between HCCs and horse welfare needs to be further examined.

Application of an equine composite pain scale and its association with plasma adrenocorticotropic hormone concentrations and serum cortisol concentrations in horses with colic

SummaryThis study assessed the application of a modified equine composite pain scale (CPS) and identified the inter‐observer reliability. Associations between CPS scores and the measured concentrations of serum cortisol ([cortisol]) and plasma adrenocorticotrophic hormone ([ACTH]) in horses presenting with colic were determined. The study design was prospective, uni‐centred and observational. The inter‐observer reliability of the adapted CPS was determined for 59 horses hospitalised for a variety of conditions. The associations between CPS, ACTH and cortisol were assessed in a further 49 horses admitted for medical or surgical colic. During hospitalisation, blood samples were obtained each morning and analysed for serum [cortisol] and plasma [ACTH]. Horses were pain scored using the adapted CPS score. Data from the most painful time point (n = 48 horses; n = 48 [cortisol]; n = 44 [ACTH]) and all data time points (n = 49 horses and n = 133 time points) were used for analysis of association between [cortisol], [ACTH] and CPS score. The CPS score inter‐observer reliability was excellent (n = 59 horses; n = 102 pain scores; weighted kappa 0.863). CPS score and [cortisol] were positively associated at the most painful time point (P &lt; 0.001) and at all data time points (P &lt; 0.001). No significant association was found between CPS score and [ACTH]. [ACTH] was associated with [cortisol] (P = 0.034) when all time points were analysed but not when only the most painful point was analysed. The significant correlation identified between CPS score and [cortisol] in medical and surgical colic cases provides physiological validation of pain scores as a marker of underlying stress in horses with colic.

Influence of season and pituitary pars intermedia dysfunction on hair cortisol concentration in horses

Hair cortisol has been demonstrated to reflect hypothalamic-pituitary-adrenal axis activity (including Cushing's disease and stress) in several species. We hypothesized that hair cortisol concentrations are increased in horses with pituitary pars intermedia dysfunction (PPID) compared with healthy adult horses and that this difference is magnified in the fall, when circulating adrenocorticotropin (ACTH) is generally the highest. Cortisol from hair collected using clippers with a #40 blade from the neck was compared between PPID horses and control horses over several months in the fall (August-December) and 1 mo in spring (May). Cortisol from hair at several sampling sites (neck, jugular furrow, sternum, and submandibular) were compared between PPID (n = 6) and control (n = 8) horses in May. Relationships between hair cortisol and ACTH were assessed in the fall. Hair cortisol when measured by weight was higher in PPID vs control horses in October and November (P ≤ 0.01) but not December (P = 0.15), May (P > 0.7), or August-September (P = 0.18). When normalized for hair length, hair cortisol was higher in PPID vs control horses in November (P = 0.0006), but not October or December (P ≥ 0.06). Hair cortisol concentrations did not differ between PPID and control horses from any collection site in May (P > 0.7). There were no consistent relationships between ACTH and hair cortisol concentrations in October, November, or December (P ≥ 0.05). These findings suggest that PPID horses have increased hair cortisol accumulation in the fall compared with control horses. Additional work is needed to clarify whether assessing cortisol per weight or per hair length is most relevant in the horse.

Increased adrenocortical response to adrenocorticotropic hormone (ACTH) in sport horses with equine glandular gastric disease (EGGD)

This study tested the hypothesis that adrenocortical function would be altered in horses with equine gastric ulcer syndrome (EGUS). Twenty-six sport horses competing at national or international levels in eventing (n=15) or endurance (n=11) were subjected to a gastroscopic examination and an adrenocorticotropic hormone (ACTH) stimulation test. Salivary cortisol concentrations were measured before (baseline) and after (30, 60, 90, 120 and 150min) IV ACTH injection (1μg/kg bodyweight). Within EGUS, two distinct diseases, equine squamous gastric disease (ESGD) and equine glandular gastric disease (EGGD), can be distinguished.ESGD was diagnosed in 8/11 (73%; 95% confidence intervals [95%CI], 43–92%) endurance horses and 5/15 (33%; 95% CI, 14–58%) eventing horses. EGGD was observed in 9/11 (82%; 95% CI, 53–96%) endurance horses and 9/15 (60%; 95% CI, 35–81%) eventing horses. The presence or severity of ESGD was unrelated to the presence or severity of EGGD. ACTH stimulation induced a larger increase in cortisol concentration in horses with moderate EGGD than in horses with mild EGGD. Cortisol concentration during the entire sampling period (total increase in cortisol concentration during the entire sampling period [dAUC], 31.1±6.4ng/mL) and the highest measured concentration at a single time point (maximal increase in cortisol concentration [dMAX], 10.3±2.3ng/mL) were increased (P=0.005 and P=0.038, respectively), indicating that horses with glandular gastric disease exhibited increased adrenocortical responses to ACTH stimulation. These results suggest that EGGD might be associated with an enhanced adrenocortical sensitivity. Further investigations are warranted to confirm the association between adrenocortical sensitivity and EGGD and to elucidate the pathophysiological mechanisms involved.

Age- and Glucocorticoid-Dependent Leptin Release by Horse Adipose Tissue: In Vitro Study

In mammals, corticosteroids overall play the greatest role in stimulation of leptin synthesis and release from the adipose tissue. Some studies have shown that changes in plasma leptin and cortisol concentrations in horses can occur independently of each other. The aim of our study on horses was to evaluate the effect of different ages on the glucocorticoid-dependent leptin release from isolated adipose tissue samples in primary culture. Subcutaneous adipose tissue samples were collected from 25 cold-blood horses aged 7 months to 11 years. Samples of adipose tissue were incubated (200 mg/mL) under control conditions (Dx0), or treated with one of two doses of dexamethasone (100 ng/mL—Dx100 and 1,000 ng/mL—Dx1000) for 12 hours. Histological examination was also conducted to obtain the mean number of adipocytes in the field of view. The medium leptin concentration was analyzed in relation to the number of adipocytes in the tissue samples. A significantly higher medium leptin concentration in Dx1000 than in Dx0 was observed only in tissue samples from foals (7–12 months of age, n = 6). Significant negative correlations were found between the age of horses and the difference in medium leptin levels Dx1000 − Dx0, as well as (Dx1000 − Dx0)/million adipocytes, and (Dx1000 − Dx100)/million adipocytes. The corticosteroids-induced secretion of leptin decreased with the age of horses.

Glucocorticoid metabolism in equine follicles and oocytes

The objective of this study was to determine whether (1) systemic and intrafollicular cortisol concentrations in horses are directly related and (2) supraphysiological levels of glucocorticoids affect in vitro maturation (IVM) rates of oocytes. Specifically, we studied the (1) changes in the intrafollicular cortisol and progesterone in context with granulosa cell gene expression during maturation of equine follicles (from 5–9 mm, 10–14 mm, 15–19 mm, 20–24 mm, and ≥25 mm in diameter) and (2) effects of cortisol supplementation on IVM rates and gene expression of equine cumulus–oocyte complexes (COCs). For these purposes, follicular fluid, granulosa cells, and COCs were collected from 12 mares (mean age 8.6 ± 0.5 yr) by transvaginal aspiration. Cortisol and progesterone concentrations in follicular fluid from follicles ≥25 mm were greater (P < 0.05) than in all other follicle classes and were positively correlated (r = 0.8; P < 0.001). Plasma concentrations of cortisol and progesterone did not differ before and after follicle aspiration (P > 0.05). In granulosa cells, gene expression of NR3C1, HSD11B1, HSD11B2, and CYP21A2 did not differ (P > 0.05) among different follicle classes. Maturation rates were similar (P > 0.05) among groups, regardless of the cortisol concentration in the IVM medium. In cumulus cells, messenger RNA expression of genes involved in glucocorticoid mechanism and apoptosis was either increased (NR3C1 and BCL2) or decreased (HSD11B2) by treatment (P < 0.01). In oocytes, gene expression of maturation markers (BMP15 and GDF9) was affected (P < 0.001) by cortisol treatment. This study demonstrates the involvement of glucocorticoids in follicle and oocyte maturation and cortisol modulation by HSD11B2 in equine COCs. Our data provide further information for understanding the normal ovarian endocrine physiology which might in turn also help improve equine assisted reproduction techniques.

Changes in Salivary Cortisol Concentration in Horses during Different Types of Exercise.

This study aimed to estimate the change of stress level in horses based on cortisol concentration levels in their saliva. A total of 61 horses were divided into the following three groups: i) tourist riding experience (TR, n = 23); ii) resting group (RR, n = 14); and iii) horse-riding education (ER, n = 24). The saliva samples of TR and ER groups were taken using plain cotton Salivettes four times a day: at 07:00 (basal), 11:00 (Exercise 1, after 1-hour exercise in the morning), 14:00 (Exercise 2, after 1-hour exercise in the afternoon), and 16:00 (Exercise 3, after 1-hour exercise in the afternoon). The saliva samples of RR were measured at the same time. The samples were analyzed using the SAS program general linear model procedure. In a percentage relative to the base value, cortisol levels in Exercise 3 were confirmed to decrease in all groups as compared to the basal value percentage in the following sequence: ER>TR>RR. The highest peak was confirmed in Exercise 2 (approximately 131%) of RR group and the lowest peak appeared in Exercise 3 (approximately 52%) of ER group. Therefore, resting without any particular exercise can also increase the stress level of horses. Thus, it is better to exercise, as exercise can reduce the stress level, even in cases when riders are clumsy or lack appropriate horse-riding experience. The results of the present study are useful to equestrian center owners and educational riding instructors in that they provide a meaningful insight into a better horse management.

Effects of season, age, sex, and housing on salivary cortisol concentrations in horses

Analysis of salivary cortisol is increasingly used to assess stress responses in horses. Because spontaneous or experimentally induced increases in cortisol concentrations are often relatively small for stress studies, proper controls are needed. This requires an understanding of the factors affecting salivary cortisol over longer times. In this study, we have analyzed salivary cortisol concentration for 6 mo in horses (n = 94) differing in age, sex, reproductive state, and housing. Salivary cortisol followed a diurnal rhythm with the highest concentrations in the morning and a decrease throughout the day (P < 0.001). This rhythm was disrupted in individual groups on individual days; however, alterations remained within the range of diurnal changes. Comparison between months showed highest cortisol concentrations in December (P < 0.001). Cortisol concentrations increased in breeding stallions during the breeding season (P < 0.001). No differences in salivary cortisol concentrations between nonpregnant mares with and without a corpus luteum existed. In stallions, mean daily salivary cortisol and plasma testosterone concentrations were weakly correlated (r = 0.251, P < 0.01). No differences in salivary cortisol between female and male young horses and no consistent differences between horses of different age existed. Group housing and individual stabling did not affect salivary cortisol. In conclusion, salivary cortisol concentrations in horses follow a diurnal rhythm and are increased in active breeding sires. Time of the day and reproductive state of the horses are thus important for experiments that include analysis of cortisol in saliva.

Serum cortisol concentration in horses with heaves treated with fluticasone proprionate over a 1 year period

The purpose of this study is to measure the effect of long-term administration of inhaled fluticasone proprionate on cortisol concentrations in heaves-affected horses. Eleven horses with heaves were treated with fluticasone at least once daily at dosages required to improve lung function or with antigen avoidance alone for 1 year. Morning serum cortisol was measured before and after 10, 30, 110, 190, 230, 280, and 320 days of treatment. Cortisol was also measured in the afternoon of day 330. Cortisol was significantly lower in the Fluticasone group on days 30, 110, and 190 when compared with the Antigen avoidance group. Cortisol measured on day 330 was also significantly lower in the Fluticasone group. Results indicate that inhaled fluticasone, when administered at therapeutic dosages, can significantly suppress serum cortisol concentrations for 8–24 h. The clinical significance of this finding remains to be ascertained, as no clinical signs were associated with this cortisol suppression.

Effects of a continuous rate infusion of butorphanol in isoflurane-anesthetized horses on cardiorespiratory parameters, recovery quality, gastrointestinal motility and serum cortisol concentrations.

To assess the cardiorespiratory parametes, recovery, gastrointestinal motility and serum cortisol concentrations in horses anesthetized with isoflurane with or without a continuous rate infusion (CRI) of butorphanol for orchiectomy. Twelve adult, intact, male horses weighing 332 ± 55 kg were included in the study. Xilazine was administered as premedication. Anesthesia was induced with ketamine and midazolam and maintained with isoflurane. Butorphanol (0.025 mg kg-1 bolus) or an equivalent volume of saline (0.9%) was given intravenously followed by a CRI of butorphanol (BG) (13 µg kg-1 hour-1) or saline (CG). Cardiorespiratory variables were recorded before (T0) and every 15 minutes for 75 minutes after the start of infusion. Serum cortisol concentration was measured at T0 and 60 minutes, and 30 minutes and 19 hours after the horse stood up. Recovery from anesthesia was evaluated using a scoring system. Gastrointestinal motility was evaluated before anesthesia and during 24 hours after recovery. There were no significant differences between groups in cardiopulmonary variables, or recovery scores or serum cortisol concentrations. A reduction in gastrointestinal motility was recorded for 60 minutes in BG. Continuous rate infusion of butorphanol in horses anesthetized with isoflurane did not adversely affect the cardiopulmonary variables monitored, or recovery scores. A small but statistically significant reduction in gastrointestinal motility occurred in the butorphanol group.

Serum cortisol concentrations in horses with colic

Few studies have evaluated cortisol concentrations in horses with colic. In humans with septic shock, high cortisol levels are associated with an increased risk of death. The objectives of this study were to compare the serum total cortisol concentrations (STCCs) in horses with colic to those without colic, and to assess whether the STCC relates to the pathological nature or outcome of the disease.STCCs were determined at presentation in horses with colic and in systemically healthy ‘control’ horses. Horses with colic were grouped based on clinical and clinico-pathological parameters at admission, treatment, lesion type and location, and outcome. Univariable and multivariable logistic regression were performed using two different outcome measures: (a) whether the horse had colic or not (yes vs. no), and (b) horse STCC (≥200 nmol/L vs. <200 nmol/L).Horses were more likely to have colic if they presented with high STCCs (≥200 nmol/L compared with <200 nmol/L). Horses with colic and with STCCs ≥200nmol/L were more likely to have moderate or severe colic signs (compared with mild colic) and heart rates >45 beats per min (compared with ≤45 beats per min). It was concluded that colic in horses is associated with elevated STCCs, and increased STCC in horses with colic appears to relate to the severity of the disease. STCCs may provide additional decision-making and prognostic information in horses with colic but further studies are required to avoid misinterpretations associated with the wide variation in STCCs.

Circadian and circannual rhythms of cortisol, ACTH, and α-melanocyte-stimulating hormone in healthy horses

Cosinor analysis was used to evaluate whether pituitary and adrenal hormones exhibit circadian rhythmicity in horses. The effect of season and animal age on their respective rhythms was also determined. In addition, the usefulness of evaluating cortisol rhythmicity for the diagnosis of pituitary pars intermedia dysfunction (PPID) was assessed. Serum cortisol concentrations (P < 0.01), but not plasma ACTH or α-melanocyte-stimulating hormone (α-MSH), showed a significant circadian periodicity in horses. An effect of season on hormone concentration was observed with plasma ACTH and α-MSH concentration greater in the fall and cortisol concentration greater in the spring (P < 0.001). Age did not affect cortisol rhythm, but it did blunt the variation in cortisol concentration in horses, similar to what has been previously reported to occur in aged people and dogs. In addition, our results suggest that clinically and diagnostically normal, non–PPID-affected horses commonly have a loss of cortisol diurnal rhythm. Therefore, measurement of circadian rhythm is not an appropriate diagnostic test for PPID.

Cortisol concentration in the saliva of horses subjected to different kinds of exercise

The aim of this study was to characterize the stress level in sport horses subjected to exercise by measuring the cortisol concentration in their saliva. The experiment was conducted on 5 groups of horses (49 animals): one control and four groups undergoing different types of exercises. The saliva samples were collected 3 × a day: late at night (between 20:00 and 23:00 h), early in the morning (between 5:00 and 8:00 h) and directly after the exercise. The concentration of cortisol was measured by the enzyme-immunoassay programme. The highest cortisol concentration was observed for the horses participating in 3-day events (8.93 nmol/dm3), whereas in the control group it was only 0.28 nmol/dm3. When compared to the cortisol concentration of other horse groups, this suggests that the stress level as measured by the cortisol concentration in saliva increases with increasing exercise intensity and its duration. The obtained results do not confirm the existence of a day rhythm of the cortisol concentration in horses. Moreover, the results may help in choosing the appropriate system of training and in improving horse welfare during competitions.

Comparison between blood serum and salivary cortisol concentrations in horses using an adrenocorticotropic hormone challenge

In horses, serum cortisol concentration is considered to provide an indirect measurement of stress. However, it includes both free and bound fractions. The sampling method is also invasive and often stressful. This is not the case for salivary cortisol, which is collected using a more welfare-friendly method and represents a part of the free cortisol fraction, which is the biologically active form. To compare salivary and serum cortisol assays in horses, in a wide range of concentrations, using an adrenocorticotropic hormone (ACTH) stimulation test, in order to validate salivary cortisol for stress assessment in horse. In 5 horses, blood samples were drawn using an i.v. catheter. Saliva samples were taken using swabs. Cortisol was assayed by radioimmunoassay. All data were treated with a regression method, which pools and analyses data from multiple subjects for linear analysis. Mean ± s.d. cortisol concentrations measured at rest were 188.81 ± 51.46 nmol/l in serum and 1.19 ± 0.54 nmol/l in saliva. They started increasing immediately after ACTH injection and peaks were reached after 96 ± 16.7 min in serum (356.98 ± 55.29 nmol/l) and after 124 ± 8.9 min in saliva (21.79 ± 7.74 nmol/l, P<0.05). Discharge percentages were also different (225% in serum and 2150% in saliva, P<0.05). Correlation between serum and salivary cortisol concentrations showed an adjusted r(2) = 0.80 (P<0.001). The strong link between serum and salivary cortisol concentrations was also estimated by a regression analysis. The reliability of both RIAs and regression found between serum and salivary cortisol concentrations permits the validation of saliva-sampling as a noninvasive technique for cortisol level assessment in horses.

Effects of various doses of ovine corticotrophin–releasing hormone on plasma and saliva cortisol concentrations in horses

To compare the effects of IV administration of various doses of ovine corticotrophin-releasing hormone (oCRH) on plasma and saliva cortisol concentrations in healthy horses and determine whether an oCRH challenge test protocol is valid for use in adult horses. 24 healthy Warmblood horses. PROCEDURES-Each horse received oCRH in saline (0.9% NaCl) via IV administration at a dose of 0 (control treatment), 0.01, 0.1, or 1.0 Mg/kg (6 horses/group). Jugular blood and saliva samples were collected simultaneously 15 minutes before and immediately prior to injection (baseline); data from these samples were pooled to provide basal values. Subsequently, 14 postinjection blood and saliva samples were both collected within a 210-minute period. Cortisol concentrations in all samples were assessed via a solid-phase radioimmunoassay. All doses of oCRH induced significant increases from baseline in both plasma and salivary cortisol concentrations. Compared with the smaller doses of oCRH, the 1.0 Mg/kg dose of oCRH induced significantly greater plasma cortisol concentrations. A relationship (r = 0.518) between basal cortisol concentrations in plasma and saliva was detected. CONCLUSIONS AND CLINICAL Relevance-For use as a CRH challenge test in adult horses, a protocol involving IV administration of a dose of at least 0.01 Mg of oCRH/kg and postinjection collection of blood samples from 10 to 180 minutes and saliva samples from 20 to 50 minutes for assessment of plasma and saliva cortisol concentrations should be sufficient. Application of such a test might be helpful to detect states of chronic activation of the hypothalamo-pituitary-adrenocortical axis at the hypothalamic level.

Evaluation of plasma catecholamine and serum cortisol concentrations in horses with colic

To evaluate plasma epinephrine and norepinephrine concentrations and serum cortisol concentration in horses with colic and assess the relationship of these variables with clinical signs, routinely measured clinicopathologic variables, and outcome in affected horses. Prospective observational study. 35 horses with colic. Blood samples were collected within 30 minutes of arrival at the veterinary hospital from horses referred because of colic. Plasma and serum samples were analyzed for cortisol, epinephrine, norepinephrine, lactate, and electrolyte concentrations and acid-base variables. Heart rate at admission and outcome (survival or nonsurvival) were recorded. Univariate logistic regression was used to calculate crude (unadjusted) odds ratios and 95% confidence intervals. Of the 35 horses with colic, 26 survived. Higher plasma epinephrine, plasma lactate, and serum cortisol concentrations were significantly associated with increased risk of nonsurvival, but plasma norepinephrine concentration was not associated with outcome. Plasma epinephrine concentration was significantly correlated with heart rate (r = 0.68), plasma lactate concentration (r = 0.87), blood pH (r = -0.83), anion gap (r = 0.74), and base excess (r = -0.81). The risk of death appears to be greater in colic-affected horses with high circulating concentrations of epinephrine and cortisol. The correlation of epinephrine with other biochemical markers of illness severity and with heart rate indicates that the degree of sympathetic activation in horses with colic can be inferred from routinely measured variables.