Peripheral Modulators of the Central Fatigue Development and Their Relationship with Athletic Performance in Jumper Horses

Monitoring the physiological inflammatory alertness in horse after road transport

The aim of this study was to assess the changes of pro-inflammatory interleukins in 10 horses subjected to road transport practices (distance of 150 km) from the training site (Messina, Sicily) to the competition centre in Syracuse (Sicily). Blood sampling and interleukins analysis were performed during a round trip transportation (transport 1 and transport 2). In particular, blood samples were collected before the transport took place (Pre), five minutes later (Post) and one hour later (Post 1 h), for each transport, in order to assess the serum concentration of IL-1α, IL-1β, IL-2 and IL-6. The results showed that the serum concentration of IL-1α decreased at Post and Post 1 h compared to the values obtained at rest condition (P < 0.05). The other interleukins analysed (i.e. IL-1β, IL-2 and IL-6) showed increased levels at Post than Rest and Post 1 h in transport 1 (P < 0.05). In transport 2 the analysed parameters showed no change throughout the analysed time points (P > 0.05); however, higher levels of IL-1α at Pre and higher IL-1β, IL-2 and IL-6 values at Post were found in transport 1 than transport 2 (P < 0.05). The increase in pro-inflammatory cytokines after transport 1 suggests the triggering of the inflammatory event and this may show that, although horses are animals accustomed to transport, this is a stressful event that could activate the well-orchestrated inflammation cascade, albeit physiological and temporary, as highlighted by the lower serum concentrations of the investigated interleukins found in transport 1 than transport 2 and by the lack of significant differences in the serum concentrations of the investigated interleukins among the time points of transport 2. It must be taken into account that enrolled animals are well-trained and healthy athletic horses participating to a jumper competition, thus, such inflammation did not occur thanks to a good balance between pro-inflammatory and anti-inflammatory cytokines which allowed a prompt restoration of homeostasis eventually impaired by the stressful event.

Blood-Based Markers for Skeletal and Cardiac Muscle Function in Eventing Horses before and after Cross-Country Rides and How They Are Influenced by Plasma Volume Shift

Horses competing in cross-country tests are subjected to high physical demands. Within the scope of this prospective longitudinal study, blood values of 20 elite eventing horses were examined before and after two- to four-star cross-country rides. The aim was to find out whether blood-based markers for skeletal muscle and cardiac muscle function change after cross-country exercise. Parameters that provide information about fluid balance, muscle enzymes, metabolites and cardiac muscle-specific markers were investigated. We developed an approach to eliminate the concentration changes caused by reduced plasma volume. Parameters were measured pre, 10 and 30 min post exercise and the next morning and were evaluated using a mixed model. Thirty minutes after exercise, most parameter concentrations changed in an exercise-dependent manner. The next morning, most exercise-related markers recovered rapidly, while creatine kinase (CK) (26% increase; p = 0.008) and lactate dehydrogenase (LDH) (15% increase; p < 0.001) showed a declining but sustained increase. Cardiac troponin I (cTnI) increased above the reference range in 40 of the 55 rides (73%) and in 18 of 20 horses in the morning after exercise.

Dynamics of training and acute exercise-induced shifts in muscular glucose transporter (GLUT) 4, 8, and 12 expression in locomotion versus posture muscles in healthy horses

Important changes in glucose transporter (GLUT) expression should be expected if the glucose influx plays a pivotal role in fuelling or connecting metabolic pathways that are upregulated in response to exercise. The aim was to assess GLUT4, 8, and 12 dynamics in response to training and acute exercise. Methods: Sixteen untrained Standardbred mares (3-4 year) performed an incremental SET at the start and end of 8 weeks harness training. M. pectoralis (PM) and M. vastus lateralis (VL) muscle biopsies were taken before and after each SET, allowing for comparing rest and acute samples in untrained (UT) and trained (T) condition using Western Blot for GLUT quantification and Image Pro v.10 for Blot analysis. Data were normalized against GAPDH. Basal GLUT-levels of PM versus VL were analysed with the Wilcoxon matched-pairs signed rank test. The effect of acute exercise or training was assessed using the Friedman test with a post hoc Dunn's. Results: Basal GLUT4 and GLUT12 protein expression were significantly higher in the VL compared to the PM (PGLUT4 = 0.031 and PGLUT12 = 0.002). Training had no effect on basal GLUT4 expression, neither in the VL (p > 0.9999), nor the PM (p > 0.9999). However, acute exercise in trained condition significantly decreased GLUT4 expression in the VL (p = 0.0148). Neither training nor acute exercise significantly changed total GLUT8 protein expression. Training significantly decreased total GLUT12 protein expression in rest biopsies, only visible in the VL (p = 0.0359). This decrease was even more prominent in the VL after acute exercise in trained condition (PVL = 0.0025). Conclusion: The important changes seen in GLUT12 expression downregulation, both in response to training and acute exercise in the horse, the downregulation of GLUT4 expression after acute exercise in trained condition and the lack of differential shifts in GLUT8 expression in any of the studied conditions, questions the importance of glucose as substrate to fuel training and exercise in healthy horses. These findings encourage to further explore alternative fuels for their involvement in equine muscular energetics.

Central and Peripheral Fatigue Evaluation during Physical Exercise in Athletic Horses by Means of Raman Spectroscopy

The evaluation of the performance levels in athletic horses is of major importance to prevent sports injuries. Raman spectroscopy is an innovative technique that allows for a rapid evaluation of biomolecules in biological fluids. It also permits qualitative and quantitative sample analyses, which lead to the simultaneous determination of the components of the examined biological fluids. On the basis of this, the Raman spectroscopy technique was applied on serum samples collected from five Italian Saddle horses subjected to a standardized obstacle course preceded by a warm-up to evaluate the applicability of this technique for the assessment of central and peripheral fatigue in athletic horses. Blood samples were collected via jugular venipuncture in a vacutainer tube with a clot activator before exercise, immediately after exercise, and 30 min and 1 h after the end of the obstacle course. Observing the obtained Raman spectra, the major changes due to the experimental conditions appeared in the (1300-1360) cm^-1 and (1385-1520) cm^-1 bands. In the (1300-1360) cm^-1 band, lipids and tryptophan were identified; in the (1385-1520) cm^-1 band, leucine, glycine, isoleucine, lactic acid, tripeptide, adenosine, and beta carotene were identified. A significant effect of exercise was recorded on all the sub-bands. In particular, a change immediately after exercise versus before exercise was found. Moreover, the mean lactic concentration was positively correlated with the Raman area of the sub-band assigned to lactic acid. In this context, the application of Raman spectroscopy on blood serum samples represents a useful technique for secondary-structure protein identification to investigate the metabolic changes that occur in athletic horses during physical exercise.

Comparison of an Antioxidant Source and Antioxidant Plus BCAA on Athletic Performance and Post Exercise Recovery of Horses

Antioxidant supplementation decreases postexercise oxidative stress but could also decrease muscle protein synthesis. This study compared the effects of three diets: low antioxidant (control, CON), high antioxidant (AO), and branched-chain amino acid high antioxidant (BCAO) supplementation on postexercise protein synthesis and oxidative stress. We hypothesized that supplementing antioxidants with branched-chain amino acids(BCAA) would reduce oxidative stress without hindering muscle protein synthesis. Eighteen mixed-breed polo horses (11 mares and 7 geldings, with age range between 5 and 18 years, were on CON diet for 30 days (from day -45 until day 0) and then were assigned to one of the treatments after the first lactate threshold test (day 0, LT). LT were also conducted on days 15 and 30 of supplemenation. Oxidative stress was assessed by measuring blood glutathione peroxidase, superoxide dismutase, and malondialdehyde concentrations before 2 and 4 hours after each LT. Muscle biopsies were taken before and 4 hours after each LT and analyzed for gene expression of protein synthesis by RTqPCR. Data were analyzed by ANOVA and compared by least-square means. A reduction in oxidative stress occurred over time (P < .05), from day 0 to day 30. An up-regulation in the abundance of muscle protein mRNA transcripts was found for CD36, CPT1, PDK4, MYF5, and MYOG (P < .05) after all lactate threshold tests, without a treatment effect. A treatment-by-exercise effect was observed for MYOD1 (P = .0041). Transcript abundance was upregulated in AO samples post exercise compared to other treatments. MYF6 exhibited a time-by-treatment effect (P = .045), where abundance increased more in AO samples from day 0 to day 15 and 30 compared to other treatments. Transcript abundance for metabolic and myogenic genes was upregulated in post exercise muscle samples with no advantage from supplementation of antioxidants with branched-chain amino acids compared to antioxidants alone.

Cortisol Variations to Estimate the Physiological Stress Response in Horses at a Traditional Equestrian Event

In many countries, horses remain involved in traditional equestrian events such as those celebrated in Menorca (Balearic Islands, Spain) every year since at least the 14th century. The present study aimed to evaluate the variations in salivary cortisol concentrations to estimate the physiological stress response in horses at the Menorca patronal festivals. Two different editions (years 2016 and 2018) of the festivals in honor of the Virgin of Grace in Maó (Menorca, Spain) were studied. Nineteen and seventeen Pure Breed Menorca stallions were included in the study, respectively. The stallions were aged between seven and twelve years. During celebrations, samples were collected before the start of the festivals between 8-9 a.m. and during the festivals at 8-9 p.m. On the second day of celebrations, the samples were collected at 8-9 a.m. and 3-4 p.m. Finally, on the day after the festivals, one sample was collected at 8-9 p.m. Additionally, a control group was sampled at 8-9 a.m., 3-4 p.m., and 8-9 p.m. Salivary cortisol concentrations were assessed by using a commercial enzyme immunoassay kit specially validated to quantify salivary cortisol in horses. Salivary cortisol concentrations did not show significant differences between sampling hours in the control group (p > 0.05). All the samples collected during festivals were significantly higher than samples of the control group (p < 0.05). Within the twenty-four hours after the end of the celebrations, cortisol concentrations returned to baseline levels and did not differ significantly from the control group (p > 0.05). Hence, the present study describes that the participation of the horses in these particular acts generate an acute and transitory stress response. Overall, the current work provides a reasonable basis for future research on the stress physiology and well-being of horses participating in traditional celebrations or similar events.

The Influence of Exercise Intensity on Tryptophan Metabolites in Thoroughbred Horses

Catabolism of tryptophan (Trp) is modulated by physical activity and provides a pool of active compounds: Trp is considered a calmative agent, kynurenine (Kyn) and 3-hydroxykynurenine (3-HKyn) show neurotoxic effects, kynurenic acid (Kyna) and xanthurenic acid (XA) have neuroprotective properties like nicotinamide (NAm), while serotonin is the neurotransmitter. The study was conducted to investigate the dependence of exercise intensity, measured by plasma lactic acid (LA) concentration, on the level of Trp, its catabolites (serotonin, Kyn, 3-HKyn, Kyna and XA), and NAm in Thoroughbred horses. A total of 18 young race Thoroughbred horses were investigated during exercise tests. Blood samples for analysis were collected: at rest, 10 min after the end of the exercise, and 60 min after the end of the exercise. Plasma LA was determined by the enzymatic method, Trp, and other metabolites using liquid chromatography coupled with mass spectrometry. In horses performing intense exercise, the concentration of LA, Kyn, XA and NAm was increased, while Trp was decreased. Significant correlations were detected for exercise-induced increase in LA and 3-HKyn, XA, and NAm. Considering the scope of changes in analyzed data, there is an expected neutral effect on the health status of exercised horses.

Effects of packing on the diurnal rhythms of respiratory and heart rates in donkeys during the hot-dry season

This study aimed to evaluate the effects of packing (load carrying) on the diurnal rhythms of respiratory and heart rates in donkeys during the hot-dry season. Twenty 2- to 3-years-old donkeys weighing 93 ± 2.7 kg were divided into two groups to serve as subjects: Group 1 was subjected to packing + trekking, while group 2 was subjected to trekking only. All donkeys trekked 20 km on each experimental day. The procedure was repeated three times at one-day intervals. Thermal environmental parameters were recorded. Respiratory rate (RR) and heart rate (HR) were measured before and immediately (15 min) after the packing and/or trekking period. Continuous recordings of parameters were performed for 27 hr at 3-hr intervals beginning 16 hr after the last packing and/or trekking period. The RR rose significantly (P<0.05) immediately after packing + trekking and trekking only, from 30.15 ± 0.5 and 27.52 ± 0.5 cycles/min before packing + trekking and trekking only, respectively, to 43.78 ± 3.0 and 46.30 ± 1.8 cycles/min after them, respectively. The HR (76.63 ± 4.5 beats/min) in the packing + trekking donkeys was higher (P<0.05) than that of the trekking-only donkeys (62.33 ± 2.7 beats/min). The acrophase and bathyphase of the HR in both groups were recorded during the photophase and scotophase, respectively, with higher values (P<0.05) in the packing + trekking donkeys than in the trekking-only donkeys. The circadian rhythms of RR and HR did not differ between the groups of donkeys. In conclusion, packing + trekking was more stressful to the donkeys, significantly increasing the HR of donkeys subjected to packing + trekking, compared with trekking only.

Selection of Image Texture Analysis and Color Model in the Advanced Image Processing of Thermal Images of Horses following Exercise

Simple Summary

Detecting horse state after exercise is critical for maximizing athletic performance. The horse’s response to fatigue includes exercise termination or exercise continuation at a lower intensity, which significantly limit the results achieved in races and equestrian competition. As conventional methods of detecting and quantifying exercise effort have shown some limitations, infrared thermography was proposed as a method of contactless detection of exercise effect. The promising correlation between body surface temperature and exercise-dependent blood biomarkers has been demonstrated. As the application of conventional thermography is limited by low specificity, advanced thermal image analysis was proposed here to visualize the link between blood biomarkers and texture of thermal images. Twelve horses underwent standardized exercise tests for six consecutive days, and both thermal images and blood samples were collected before and after each test. The images were analyzed using four color models (RGB, red-green-blue; YUV, brightness-UV-components; YIQ, brightness-IQ-components; HSB, hue-saturation-brightness) and eight texture-features approaches, including 88 features in total. In contrast to conventional temperature measures, as many as twelve texture features in two color models (RGB, YIQ) were linked with blood biomarker levels as part of the horse’s response to exercise.

Abstract

As the detection of horse state after exercise is constantly developing, a link between blood biomarkers and infrared thermography (IRT) was investigated using advanced image texture analysis. The aim of the study was to determine which combinations of RGB (red-green-blue), YUI (brightness-UV-components), YIQ (brightness-IQ-components), and HSB (hue-saturation-brightness) color models, components, and texture features are related to the blood biomarkers of exercise effect. Twelve Polish warmblood horses underwent standardized exercise tests for six consecutive days. Both thermal images and blood samples were collected before and after each test. All 144 obtained IRT images were analyzed independently for 12 color components in four color models using eight texture-feature approaches, including 88 features. The similarity between blood biomarker levels and texture features was determined using linear regression models. In the horses’ thoracolumbar region, 12 texture features (nine in RGB, one in YIQ, and two in HSB) were related to blood biomarkers. Variance, sum of squares, and sum of variance in the RGB were highly repeatable between image processing protocols. The combination of two approaches of image texture (histogram statistics and gray-level co-occurrence matrix) and two color models (RGB, YIQ), should be considered in the application of digital image processing of equine IRT.

Monitoring Performance in Show Jumping Horses: Validity of Non-specific and Discipline-specific Field Exercise Tests for a Practicable Assessment of Aerobic Performance

Show jumping is a highly specialized equestrian discipline that requires technical skill but also power and fitness. Monitoring the horses’ aerobic performance is therefore essential in order to verify whether the training has induced the desired cardiovascular and muscular adaptations. This study therefore aimed at evaluating the validity of non-specific and discipline-specific field exercise tests for objective evaluation of aerobic performance in show jumpers. For this purpose, data obtained from horses competing at Junior and Young Rider level during show jumping competitions as well as field exercise tests were retrospectively analyzed. The effect of the level of difficulty, the horses’ age, the penalty score and the horses’ previous level of performance on blood lactate concentrations after show jumping competitions (100 observations in 49 horses) was evaluated by linear mixed effects models (horse as random effect). Estimated marginal means significantly increased from 140 (4.1 mmol/L) to 150 cm (5.2 mmol/L) classes (P = 0.02). Furthermore, post-exercise lactate values significantly increased with the horses’ age (P = 0.001). Another group of 12 horses performed a standardized incremental field exercise test on a track (SET_track), a standardized show jumping course (SET_course) and a standardized grid exercise (SET_grid) each on three consecutive days. Indices of aerobic performance, derived from the SET_track [velocity at a heart rate of 140 bpm (V₁₄₀) and at a lactate concentration of 2 mmol/L (V_La2)] were highly correlated with heart rate (V₁₄₀: r = −0.75, P = 0.005; V_La2: r =−0.66, P = 0.02) and lactate (V₁₄₀: r = −0.73, P = 0.02; V_La2: r = −0.72, P = 0.02) in response to SET_course as well as heart rate during SET_grid (V₁₄₀: r = −0.73, P = 0.02; V_La2: r = −0.76, P = 0.01). Subjective rating of muscular fatigue was significantly correlated to the mean heart rate during SET_course (r = −0.64, P = 0.05) and SET_grid (r = −0.74, P = 0.02) but not to the aerobic indices calculated from SET_track. Besides non-specific incremental field tests, performance monitoring in show jumpers should therefore also include discipline-specific tests that more closely reflect the internal load induced by show jumping competitions.

Dynamic Metabolic Response, Clotting Times and Peripheral Indices of Central Fatigue in Horse Competing in a 44 Km Endurance Race

A deep knowledge on metabolic response of athlete horse to exercise is of paramount importance for the development of optimal training programs to attain equilibrium between good performance and animal welfare. This study investigated the dynamic change of metabolic, clotting times and peripheral indices of central fatigue in horses competing in an official 44 km endurance race.  From 6 horses blood samples were collected at rest (T_PRE), within 5 minutes from the end of race (T_PE5), after 30, 60 minutes after the end of race (T_PE30 and T_PE60) to investigate the values of blood lactate, glucose, platelets (PLTs), serum leucine, isoleucine, valine, tryptophan, the ratio between tryptophan and branched-chain amino acids (BCAAs) levels (Try/BCAAs), total proteins, non-esterified fatty acids, plasma thrombin time (TT), prothrombin time (PT), activated partial thromboplastin time and fibrinogen (Fb). Lactate, PLTs, non-esterified fatty acids, BCAAs and Try/BCAAs showed higher values at T_PE5, T_PE30and T_PE60than T_PRE(P < .0001); glucose showed lower values at T_PE5, T_PE30and T_PE60than T_PRE(P < .0001). Higher TT values were found at T_PE5, T_PE30and T_PE60than T_PRE, and at T_PE5than T_PE30 and T_PE60(P < .0001); Fb was higher at T_PE5than T_PRE, T _PE30and T_PE60(P < .0001). This survey confirms that horses performing prolonged physical exercise experienced glycolysis, lipid mobilization and amino acid metabolism to provide substrates as fuel for muscle contraction.

Accuracy of a heart rate monitor for calculating heart rate variability parameters in exercising horses

Heart rate is evaluated in exercising horses to monitor the level of fitness to exercise, and it is usually acquired using heart rate monitors (HRM) or telemetric electrocardiograms (ECG). While HRM are commonly available and easy-to-use for horse's owners, ECG is a more expensive equipment requiring user's experience. Interest for heart rate variability (HRV) in horses is increasing for both research and clinical purposes. HRV is usually calculated from interbeat intervals (IBI) obtained by ECG. The aim of this study was to determine the accuracy of an HRM to detect IBI for the calculation of HRV in both resting and exercising horses. Simultaneous ECG and HRM recordings were performed on 13 horses and ponies under normal training conditions for at least 45 minutes. IBI from ECG were corrected using a dedicated software. IBI from HRM were exported without correction. Two HRV-parameters were calculated on both recordings for resting and exercising periods: the standard deviation of R-R intervals (SDRR) and the root mean square of successive differences (RMSSD). Agreement and concordance between the two systems were determined using Bland-Altman plot and Lin's correlation coefficient, respectively. Effects of variables were consequently assessed. For both HRV-parameters during resting and exercising periods, the means of the differences between the two systems were lower than 0.47 ms with a correlation coefficient higher than 0.999. Height, weight and body condition score had no effect on the results. The studied HRM could be of interest as easy-to-use device for obtaining HRV-parameters SDRR and RMSSD in resting and exercising horses.