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Summary Reasons for performing study: Mangalarga-Marchador is a popular 4-gaited Brazilian horse breed; however, there is little information about their metabolic and physiological response to exercise. Objectives: To measure physiological and metabolic responses of the Mangalarga-Marchador to a simulated marcha field test and to compare these responses between 2 types of marcha gaits (picada and batida). Methods: Thirteen horses were used in the study and randomly assigned to either the picada or batida gait for the simulated marcha field test (speed ∼3.2 m/s; 30 min; load ∼80 kg). Measurements: Included body composition, heart rate (HR), respiratory rate (RR), glucose (GLUC), lactate (LACT), packed cell volume (PCV), total plasma protein (TPP), albumin, urea, creatinine, total and HDL cholesterol, triglycerides, creatine kinase, alanine, glutamate and glutamine (GLN). Measurements were obtained pretest (control/fasting), immediately after simulation (T0), and 15 (T15), 30 (T30) and 240 (T240) min after the simulation. Lactate (LACT) was measured at T0, T15 and T30. Data were analysed using ANOVA, Tukey's test and t tests with significance set at P

Summary Reasons for performing study: Studies have demonstrated increases in mRNA expression for inflammatory cytokines following exercise in horses and have suggested those markers of inflammation may play a role in delayed onset muscle soreness. However, measurement of mRNA expression in white blood cells is an indirect method. No studies to date have documented the cytokine response to exercise directly in muscle in horses. Hypothesis: This study tested the hypothesis that exercise increases cytokine markers of inflammation in blood and muscle. Methods: Blood and muscle biopsies were obtained from 4 healthy, unfit Standardbred mares (∼500 kg). The randomised crossover experiment was performed with the investigators performing the analysis blind to the treatment. Each horse underwent either incremental exercise test (GXT) or standing parallel control with the trials performed one month apart. During the GXT horses ran on a treadmill (1 m/s increases each min until fatigue, 6% grade). Blood and muscle biopsies were obtained 30 min before exercise, immediately after exercise and at 0.5, 1, 2, 6 and 24 h post GXT or at matched time points during the parallel control trials. Samples were analysed using real time-PCR for measurement of mRNA expression of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-1 (IL-1). Data were analysed using t tests with the null hypothesis rejected when P0.10) in IL-1, IL-6, IFN-gamma or TNF-alpha during control. Exercise induced significant increases in IFN-gamma, IL1 and TNF-alpha in blood and significant increases in IFN-gamma, IL-6 and TNF-alpha in muscle. There were no significant changes in mRNA expression of IL-1 in muscle or IL-6 in blood following the GXT. These cytokine markers of inflammation all returned to preGXT levels by 24 h post GXT. Conclusion: High intensity exercise results in a transient increase in the expression of inflammatory cytokines in muscle and blood.

Summary Reasons for performing study: Many nutraceuticals are used as equine supplements without their efficacy having been scientifically tested. Black tea, cranberries, orange peel and ginger are a few of those nutraceuticals that warrant further study. Objective: To test the effects of single doses of black tea, cranberry, orange peel and ginger extract on markers of oxidative stress and antioxidant status following exercise in horses. Methods: In Study 1, 9 mature, healthy but unfit Standardbred mares were administered 2 l of a control (water), orange peel extract (30 g extract) or decaffeinated black tea extract (28 g extract). In Study 2 the same mares were administered 2 l of a control (water), cranberry extract (30 g extract) or ginger extract (30 g extract). In each study, mares were given the extracts via nasogastric tube 1 h before performing a graded exercise test (GXT), in a randomised crossover design with at least 7 days between GXTs. Blood samples were collected at rest, at fatigue, and 1 and 24 h post exercise and analysed for lipid hydroperoxides (LPO), total glutathione (GSH-T), glutathione peroxidase (GPx), α-tocopherol (TOC), β-carotene (BC) and retinol. Data were statistically analysed using a repeated measures ANOVA. Results: In Study 1 there was no effect of treatment for LPO, GSH-T, GPx, TOC or BC. Retinol was higher for both tea (P = 0.0006) and water (P = 0.004) than for orange peel. In Study 2 there was no treatment effect for LPO, GPx, GSH-T, RET, BC or TOC. Conclusions: The results show that a single dose of various nutraceuticals in exercising horses do not produce an effect on either oxidative stress or antioxidant status and further investigation is needed as to whether long-term supplementation would enhance these effects.

Summary Reason for performing study: Older horses have an increased risk of hyperthermia due to impaired cardiovascular function. While many studies have investigated thermoregulation in horses during exercise, none have investigated the effects of ageing. Objective: To test the hypothesis that there is a difference in thermoregulation during exercise and plasma volume (PV) in young and old horses. Methods:Study 1: 6 young (Y, 7.7 ± 0.5 years) and 5 old (O, 26.0 ± 0.8 years) unfit Standardbred mares (507 ± 11 kg, mean ± s.e.) ran on a treadmill (6% grade, velocity calculated to generate a work rate of 1625 watts) until core temperature reached 40°C. Core (CT), skin (ST), rectal temperature (RT) and heart rate (HR) were measured every min until 10 min post exertion. Packed cell volume (HCT), lactate (LA) and plasma protein (TP) were measured in blood samples collected before, at 40°C and every 5 min until 10 min post exercise. Sweat loss was estimated using bodyweight. Study 2: Plasma volume was measured in 26 young (8.2 ± 0.7 years) and 8 old (26.6 ± 0.7 years) Standardbred mares (515 ± 12 kg) using Evans Blue dye. Pre-exercise blood (rBV) and red cell (rRCV) volumes were calculated using PV and HCT. Data analysis utilised repeated measures ANOVA and t tests and data are expressed as mean ± s.e. Results: Old horses reached 40°C faster (998 ± 113 vs. 1925 ± 259 s; P 0.05) post exercise. Age did not alter (P>0.05) CT, ST, RT, LA, HCT or TP. Plasma volume was greater in Y vs. O horses (P

Summary The purpose of the present study was to determine whether the training-induced hypervolemic response seen in the horse is associated with aldosterone-mediated renal mechanisms affecting sodium conservation during the first days of training. Five healthy, Standardbred mares (weight 450–500 kg, age 4–8 years) that were unfit, but accustomed to running on the treadmill, were used to test the hypothesis that repeated submaximal exercise would alter plasma aldosterone (ALDO) concentration and renal excretion of electrolytes in horses within the first 3 days of training. The experiment consisted of a 2 week housing equilibration period followed by a 1 week control period and a 3 day exercise training period (30 min/day at 60% VO2max). During control, ALDO and renal fluid and electrolyte losses were measured for 24 h on 3 separate days. Renal function (urine volume [UV], 24 h excretion of Na+, K+ and CI- [UNA+V, UK+V, UClV], clearance of Na+ [CNa+], K+ [CK+] and Cl− [CCl-], creatinine [CCr], osmotic substances [Cosm], and solute-free water [FWC], and the fractional excretion of Na+, K+ and Cl−) and ALDO were measured for an additional 3 consecutive days during the training period. There were no differences (P>0.05) in any variable during the control period. Plasma volume increased (+18.7%, P

Summary It has long been known that body mass and, more specifically, lean body mass are strongly correlated with maximal oxygen uptake (VO2max) in man and animals. However, there are no data to date describing this phenomenon in the horse. The purpose of this paper is to examine the relationship between body composition and VO2max in the horse. Twenty-three healthy and unfit Standardbred mares performed an incremental exercise test (GXT) to measure VO2max. Rump fat thickness (RTH), a measure of fat covering, was measured using B-mode ultrasound. Plasma volume, total blood volume and red cell volume were determined, using the Evan's Blue dye dilution technique and packed cell volume. VO2max was correlated with body mass (r = 0.541; P

The purpose of the study was to determine whether 12 weeks of exercise training would affect plasma glucose and plasma insulin concentrations in young and older Standardbred mares. Eighteen healthy, unfit mares representing 3 age groups were used: young (Y = 6.8 +/- 0.4 years; n = 6), middle-aged (MA = 15.2 +/- 0.4; n = 6), and old (O = 27.0 +/- 0.2; n = 6). Pre- and post-training incremental exercise tests (GXT) were performed to measure plasma glucose and insulin concentration from immediately after, until 120 min postexercise. Training consisted of exercise 3 days/week (weeks 1-8) and 4 days/week (weeks 9-12) at a submaximal intensity (approximately 60% of pretraining HRmax) for approximately 30 min/day. Old mares had lower levels of glucose after the GXT when compared to Y and MA mares (P0.05). There was also a time-by-age interaction (P = 0.003) in that, at 120 min post-GXT, glucose levels had not returned to pre-exercise values. Plasma glucose concentrations, in response to acute exercise, were not altered by training for any age group (P0.05). Prior to exercise training, O mares had higher plasma insulin compared to Y and MA mares at 120 min postexercise (P0.05), and insulin was also elevated in O mares compared to all other time points at 120 min post-GXT (P0.05). Training resulted in increased plasma insulin concentrations at 120 min post-GXT in all age groups (P0.05). In conclusion, age affected glucose and insulin responses to acute exercise prior to and after 12 weeks of exercise training. With regards to insulin, 12 weeks of exercise training resulted in a postexercise rebound hyperinsulinaemia, which may be related to an increased need for glycogen repletion in the muscle. These factors are important in considering the ability of an older horse to tolerate exercise.

Summary Several body systems make critical contributions to the defence of blood volume, mean arterial pressure and plasma tonicity. These mechanisms ensure adequate blood flow to the working muscles and vital tissues along with the provision of adequate fluid volume for sweating and thermoregulation. The present paper integrates data from several recent studies that examined the neuroendocrine control of cardiovascular function in exercising horses. These studies focused on the effects of exercise on plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin activity (PRA) and aldosterone (ALDO), hormones associated with the regulation of blood pressure, the distribution of blood flow and the long term control of vascular fluid volume. Data were collected during incremental and endurance exercise, following frusemide administration and after splenectomy. Increases in ANP during exercise were associated with increased atrial pressure and stretching of the atrium. Increases in PRA and ALDO are correlated with increases in sympathetic activity during incremental exercise and with decreases in plasma Na+ and CI− concentrations. Plasma AVP increases later in exercise in response to fluid losses, increases in plasma osmolality, and decreases in right atrial pressure. AVP has a minimal effect on renal function during exercise and may be more important during recovery, when it stimulates thirst and drinking. Frusemide and splenectomy decrease atrial pressure, resulting in lower plasma ANP and greater plasma AVP concentrations during steady-state submaximal exercise. The ANP and AVP responses are part of the neuroendocrine action of the cardiopulmonary baroreflex which appears to mediate the accommodation of the mobilised splenic reserve in the horse. In summary, exercise induced increases in ANP, AVP, PRA and ALDO in the horse appear to play an important role in cardiovascular homeostasis.

Summary Reasons for performing study: Heart rate is one of the most commonly measured variables in equine exercise physiology and relative exercise intensity commonly expressed as % of maximal heart rate. A number of influences affect maximal heart rate (HRmax), including age of the horse but other factors have not been described. Objectives: To determine if fitness, health status, gender, breed, athletic use, body mass, in addition to age, are predictive of HRmax in the horse. Methods: Maximal heart rate data from 328 horses which underwent treadmill exercise tests at 5 different laboratories were obtained retrospectively. Univariable linear regression analyses were performed on individual variables. Multiple linear regression analysis using a backward elimination modelling procedure was then used to relate the observed HRmax values simultaneously with different predictive variables. Variables were retained in the final regression model if they or any of their categories were significantly predictive of HRmax at P

Summary Reasons for performing study: Horses in training tend to become inappetant; however, the mechanism responsible for this training-induced inappetance is not known. Hypothesis: Training and/or ulcers alter the feed intake (FI) and hormonal and/or biochemical (active ghrelin, leptin, glucose, insulin and cortisol) responses to acute high intensity exercise. Methods: Eight Standardbred mares underwent 3 interval exercise tests (IET) and 3 parallel control tests (CON) before (IET1) and after 8 weeks of training (IET2) and after treatment for gastric ulcers (IET3). Plasma samples were taken before (0 min), during (last 10 sec of velocities eliciting 40, 100 and 20% VO2max), and after (30 min, 60 min, 24 h) exercise (EX) or CON tests for RIA and colorimetric measurement of the concentrations of the above parameters. Samples were also collected before and after feeding. Horses were trained at a work intensity of 70% HRmax for 30 min/day, 5 days per week with FI measured daily. Results: There were no changes (P>0.05) in any variable during the parallel control trials. However, there was a mismatch between FI and digestible energy (DE) requirements (P

Introduction In theory, splenic reserve mobilization should elicit a cardiopulmonary baroreceptor mediated neuroendocrine response (the Gauer-Henry reflex). Six intact (IN) and 5 (SP) splenectomized Standardbred mares (421–491 kg, ∼9 yr) performed 10 min of treadmill exercise (80% VO2max) to test the hypothesis that hemodynamic and endocrine responses to exercise would differ between IN and SP horses Methods Blood samples were obtained before and at 1, 2, 4, 6, 8 and 10 min of exertion. Right ventricular pressure (RVP), right atrial pressure (RAP), arterial pressure (MAP), heart rate (HR), and cardiac output (CO) were measured and total peripheral resistance (TPR) calculated. Plasma atrial natriuretic peptide (ANP) and vasopressin (AVP) concentrations were measured using RIA. Data analysis used ANOVA for repeated measures and SNK. Significance was set at P0.05) between IN and SP for any variable at rest. All variables except TPR and RAP increased (P