Search

Clenbuterol, (RS)-1-(4-amino-3,5-dichlorophenyl)-2-(tert-butylamino)ethan-1-ol, as Ventipulmin is an FDA approved β2 agonist medication for the management of airway obstruction in horses. Administration above the FDA approved doses for clenbuterol produces repartitioning effects, which have led to restrictions on its use in human athletics and Quarter Horse and Thoroughbred racing. Clenbuterol, however has long been used therapeutically at FDA approved doses in Harness racing. The goal of this study was to identify a withdrawal time guideline for its use at FDA approvsed dose levels in Harness racing, where horses may start at seven-day intervals. Eight healthy, moderately fit Standardbred horses (4 mares, 4 geldings, weight 491±40 kg, age 13±2 years) were administered 0.8 μg/kg of clenbuterol as Ventipulmin syrup twice daily (BID) for three days. Blood samples were collected prior to dosing and at 1, 24, 48 and 96 h post administration. Clenbuterol was quantified in all samples using the New York Drug Testing and Research Laboratory ISO-17025 Racing and Medication Testing Consortium (RMTC) accredited quantitative procedure. The lower limit of quantitation of the method was 1.0 pg/ml, and three data points at 96 h post administration were censored. One horse developed diarrhoea and data from this horse was excluded from the overall analysis. Plasma regulatory thresholds were calculated using the 95/95 tolerance method and Gauss Camp Meidell at P=0.05 and P=0.001. Horses were also evaluated for effects of clenbuterol on body composition using body mass and ultrasound measurements of rump fat thickness. There were no effects (P>0.05) of clenbuterol on any of the measures including fat mass and fat free mass and thus no repartitioning effect was observed. The pharmacokinetic data and the 96 h data set support the therapeutic use of clenbuterol in Harness horses at the FDA approved 0.8 μg/kg BID dose for three days and suggest a 41 pg/ml regulatory threshold for a 96 h withdrawal time with a P=0.001 probability of randomly exceeding this regulatory threshold.

The athletic horse, despite being over 50% muscle mass, remains understudied with regard to the effects of exercise and training on skeletal muscle metabolism. To begin to address this knowledge gap, we employed an untargeted metabolomics approach to characterize the exercise-induced and fitness-related changes in the skeletal muscle of eight unconditioned Standardbred horses (four male, four female) before and after a 12-week training period. Before training, unconditioned horses showed a high degree of individual variation in the skeletal muscle metabolome, resulting in very few differences basally and at 3 and 24 h after acute fatiguing exercise. Training did not alter body composition but did improve maximal aerobic and running capacities (p < 0.05), and significantly altered the skeletal muscle metabolome (p < 0.05, q < 0.1). While sex independently influenced body composition and distance run following training (p < 0.05), sex did not affect the skeletal muscle metabolome. Exercise-induced metabolomic alterations (p < 0.05, q < 0.1) largely centered on the branched-chain amino acids (BCAA), xenobiotics, and a variety of lipid and nucleotide-related metabolites, particularly in the conditioned state. Further, training increased (p < 0.05, q < 0.1) the relative abundance of almost every identified lipid species, and this was accompanied by increased plasma BCAAs (p < 0.0005), phenylalanine (p = 0.01), and tyrosine (p < 0.02). Acute exercise in the conditioned state decreased (p < 0.05, q < 0.1) the relative abundance of almost all lipid-related species in skeletal muscle by 24 h post-exercise, whereas plasma amino acids remained unaltered. These changes occurred alongside increased muscle gene expression (p < 0.05) related to lipid uptake (Cd36) and lipid (Cpt1b) and BCAA (Bckdk) utilization. This work suggests that metabolites related to amino acid, lipid, nucleotide and xenobiotic metabolism play pivotal roles in the response of equine skeletal muscle to vigorous exercise and training. Use of these and future data sets could be used to track the impact of training and fitness on equine health and may lead to novel predictors and/or diagnostic biomarkers.

Two groups of unfit Standardbred mares (adult: 9-14 years, 540 kg, n=7) and old (20-25 years, 530 kg, n=5) were used to test two hypotheses, first, that aging and training would alter plasma and muscle glutamine [Gln] and glutamate [Glu] and second, that aging and training would alter Glut-4 expression in skeletal muscle. All animals were housed on pasture with free access to grass and all received hay and supplementation with a commercially prepared supplement (15% crude protein and 3.00 Mcal/kg dry matter) in individual stalls. Mares were fed to meet or exceed NRC (2007) nutrient recommendations for moderate to heavy exercise. The mares were exercise trained in a free-stall motorised circular exercise machine for 30 min/d, 5 d/week, for 8 weeks. Work intensity during training was set at a relative intensity of ~60% of the maximum heart rate, previously determined during an incremental exercise test (GXT). Blood samples and muscle biopsies (gluteus) obtained before and after 8 weeks of training were used for measurement of [Gln], [Glu] and Glut-4 abundance. Samples were collected before the initiation of training and at 24 h after cessation of last bout of exercise in the training period. All samples were immediately frozen in liquid nitrogen and stored at -80 °C until enzymatic analysis for [Gln], [Glu] and Western Blot analysis for Glut-4 protein abundance. Data were analysed by one-way or two-way ANOVA for repeated measures and the Pearson correlation method. Post-hoc differences were identified with the Tukey test. Significance was set at P0.05) in muscle [Glu] due to aging. Training decreased (P0.05) due to training. Glut-4 abundance analysis did not differ (P>0.05) between the young adult and old horses; however, there was a trend (P=0.063) towards an effect of training when samples from both groups were pooled. It was concluded that training and aging produce changes in plasma and muscle [Gln], which may affect immune function in athletic horses, but not in Glut-4.

While exercise has been found to change the faecal microbiome (FM) in laboratory animals exposed over weeks, no studies have identified immediate changes in the FM associated with short spans of intense exercise, ~5 min. The purpose of this study was to test the hypothesis that acute intense exercise would alter the FM in horses. Each horse performed two rounds of testing undergoing both a graded exercise test (GXT) and a parallel standing control (SC) trial before (GXT1 and SC1) and after (GXT2 and SC2) 12 weeks of exercise training. Rectal faecal samples were taken 24 h before and after testing. Bacterial community analysis was done by sequencing the 16s rRNA (V3-V4) region via Illumina Miseq. The relative abundance of the genus Clostridium significantly decreased in SC1 (P0.05). Our results indicate that very intense acute exercise does not alter the faecal microbiome of the Standardbred race horse and that 12 weeks of exercise training does not alter that response.

Anecdotal evidence suggests high horse turnover is a concern in the field of equine assisted services (EAS) with potential negative effects on sustainability. Members of key EAS organizations (American Hippotherapy Association; Professional Association of Therapeutic Horsemanship, International; eagala; Certified Horsemanship Association for a total of 26,000 recipients) were surveyed to characterize horses in EAS programs, their use, and causes of retirement. We expected respondents to indicate horses remained in their programs for relatively short periods of time and list behavior as a leading cause of retirement. The survey (QualtricsⓇ) was distributed via email using a repeat contact strategy of 4 contacts spaced 2–4 wk apart. Descriptive statistics were computed in SAS (v 9.4). Kendall's correlation with Bonferroni correction was used to analyze relationships of retirement causes and longevity with selection procedures and workload. Respondents (n = 176 completed responses; 0.14% response rate) reported 12 ± 8 (mean ± SD) horses and ponies were active in their programs. Animals ranged in age from less than 5 yr (2 ± 5% of animals in program) to 36–40 yr (0.1 ± 1.3%) with the greatest number falling between 16 and 20 yr (34% ± 22%). Donation (40 ± 34% of animals in program), purchase from private owner (23 ± 31%), and free lease (18 ± 26%) were reported as the most common means of acquiring horses and ponies. Animals had been active in the program for less than one yr (4.5 ± 12% of animals in program) to over 20 yr (4.4 ± 18%) with the greatest percentage of animals active for 1–5 yr (37 ± 35%) followed by 6–10 yr (31 ± 31%). Respondents indicated horses and ponies typically worked anywhere from 0 to 1 h/wk (0.6% of respondents) to 42–48 h/wk (0.6%) with the largest number working 4–8 h/wk (20%). When asked reasons for retiring horses and ponies, respondents ranked (1 = most frequent; 7 = least frequent) age (2, 1–3; median, IQR), behavior (2, 1–3), and unsoundness (2, 1–3) as the most frequent reasons followed by burnout (2.5, 1–4), other health issues (3, 2–3), death (4, 2–4), lease expiration (5, 3.5–5), and other reasons. Selection procedures and workload were not significantly corelated with reason for retirement or longevity. Further research is needed to understand how burnout, a behaviorally assessed state, differs from behavioral reasons for retirement and its implications. Collection and analysis of other variables, potentially at an individual animal level, is needed to further our understanding of factors contributing to horse longevity and retirement.

Exercise has a significant effect on different physiological systems in the body of human and animals. Only limited numbers of published studies in laboratory animals or humans have shown the effect of exercise on the gut microbiota, and no studies have shown this effect in horses. In this study, 8 horses (4 mares, 4 geldings) were exercise trained for 12 weeks, and 4 additional mares were used as a parallel seasonal control. To identify bacterial community changes over time for both groups, rectal faecal samples were collected, DNA was extracted, and the 16S rRNA gene (V3-V4) was sequenced using the Illumina Miseq platform. One-way ANOVA, Shannon diversity index, and Principal Coordinate Analysis (PCoA) were used to identify differences between and among samples. The exercise training group showed significant changes in the levels of Bacteroidetes, Proteobacteria, and Spirochaetes phyla (P0.05). Moreover, with training two genera significantly changed in their relative abundance over time, namely Clostridium and Dysgonomonas (P

An antioxidant derived from a variety of melon purported to be high in superoxide dismutase was fed to horses and the effect on performance and recovery was measured following repeated daily bouts of intense exercise. In a cross-over design study, six unfit Standardbred mares were fed this antioxidant at a rate of 2.0 IU/kg body weight (BW)/d as part of the daily ration for 4 weeks before undergoing a simulated race test (SRT) repeated over a 3-day period. The SRT, designed to simulate the training of Standardbreds, consisted of a 2 min warm-up at 6 m/s followed by a high speed run to fatigue at 125% of the speed calculated to correspond to the horse’s maximal aerobic capacity (VO2max) as determined in a baseline incremental exercise test. Measurements included VO2 and the VO2 recovery time, VO2 at the point of recovery, run time, as well as plasma lactate, and plasma cortisol. Oxidative stress was measured by assessing malondialdehyde (MDA). The results from the study demonstrated that there were no differences (P>0.05) in mean values for the plasma concentrations of lactate, cortisol, or MDA. However, when supplemented with this antioxidant, there was an observable pattern with a small-to-medium effect size of an increase average run time of 14 s. Another important observation was that despite the longer run time, there was a moderate effect for a faster VO2 recovery time. The data suggest that supplementation with 2.0 IU/kg BW of this antioxidant had a modest but non-significant effect on performance and recovery time. Additionally, it did not negatively impact physiology in untrained Standardbred mares.

Six Standardbred mares (age 12±2 years, body weight 502±63 kg; mean ± standard deviation) were given 1.6 µg/kg acylated human ghrelin or vehicle treatment as an intravenous bolus in a randomised, cross-over design to test the hypothesis that exogenous ghrelin infusion would increase feed intake and alter metabolic parameters of energy homeostasis, leptin, glucose, insulin and cortisol. After the horses had initial access to hay cubes for 1.5 h, doses were given and hay cubes were available once again. Leftover feed was weighed 6 times over each of the 24 h testing periods. Blood samples for measurement of active ghrelin, growth hormone, leptin, glucose, insulin and cortisol were taken at time 0 (immediately before infusion) and 20, 40, 60, 80, 100, 120, 240, 480, and 720 min post-infusion. Every 10 min, the horses’ behaviour was recorded for eating, drinking, resting, and other behaviours. Ghrelin infusion did not increase (P≯0.05) feed intake in the mares as a group, but did increase feed intake (P

The chronic bradycardia seen in several species after intense exercise training may be due to autonomic mechanisms, non-autonomic mechanisms, such as increased pre-load, or a combination of the two. Thirteen, healthy, unfit Standardbred mares were split into two groups: young (age 12±1 yr; mean ± standard error, n=8) and old (age 22±1 yr, n=5) to test the hypothesis that there would be age and training related differences in resting heart rate (RHR), intrinsic heart rate (IHR), maximal heart rate (HRmax) and plasma volume (PV). Mares were trained 3 d/wk at 60% HRmax for 20 min and gradually increased to exercising 5 d/wk at 70% HRmax for 30 min and RHR, IHR, HRmax, and PV were measured prior to and after the 8 wk training period. There were no age related differences (P≯0.05) between young and old mares before (41±2 vs. 42±2 beats per minute (bpm); 86±5 vs. 80±4 bpm) or after training (35±1 vs. 34±1 bpm; 81±6 vs. 78±2 bpm) for RHR and IHR respectively. RHR was decreased (Pmax than the old horses (P

This study tested the hypothesis that old and young mares exhibit different endocrine responses to a frequently sampled intravenous glucose tolerance test (FSIGT) and different cytokine profiles in blood, adipose and muscle tissues. It was also hypothesised that exercise training alters endocrine and tissue cytokine profiles. Pilot data from 15 mixed background horses indicated tissue differences in cytokine profiles. For the main study, six old (22.0±0.7 years) and six young (7.3±0.6 years; mean±SE) unfit Standardbred mares were tested pre- and post-training. Exercise training occurred three days/week for 15 weeks at ~60% maximum heart rate. Plasma insulin and glucose concentrations were measured via radioimmunoassay and enzyme-electrode interface, respectively. Samples of blood, middle gluteal muscle (RM), and subcutaneous adipose tissue from the neck (NF) were collected pre- and post-training for mRNA quantification. Minimal model analysis of FSIGT, repeated measures ANOVA and Pearson Product Moment were used to analyse data. The null hypothesis was rejected when P≤l0.10. Post-training, old and young mares improved insulin sensitivity (SI) (P=0.08, P=0.01, respectively) and disposition index (P=0.04, P

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 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

The objective of this experiment was to test the hypothesis that ageing and training alter plasma concentrations of the peptide hormone leptin. The rationale for the study is based on prior investigations performed at Rutgers University, where published reports documented that ageing disrupts the immune and endocrine responses to acute exercise. The training period for mature young (7.3 ± 0.6 years; n = 6) and old (22 ± 0.7 years; n = 6) (mean ± SE) Standardbred mares was the duration of the summer of 2009 at the Rutgers University Equine Exercise Physiology Laboratory. Mares exercise trained in groups of six in a free-stall motorized circular equine exercise machine for 30 min, three times per week. Each mare performed a graded exercise test before beginning the training, after 8 weeks and after 16 weeks of training. There was no difference in body mass due to age (P>0.10). Training caused an increased body mass in both old and young mares (P

This study tested the hypothesis that phenylbutazone would block the exercise-induced increase in cytokine markers of inflammation in blood. Blood samples were obtained from unfit Standardbred mares (age 10 ± 4 years, ~500 kg) before and after three different trials (standing control (CON), n = 9; exercise with phenylbutazone (EX-bute), n = 9; and exercise with water, n = 9). Comparisons were made for data collected in three trials, one where each horse underwent an incremental exercise test (graded exercise test (GXT)) where they were administered water as a placebo, a GXT following phenylbutazone administration (2 g given orally 2 h before the GXT) or standing parallel control where they stood quietly in stalls. During the GXT, horses ran on a treadmill (1 m s − 1 increases each min until fatigue, 6% grade). Blood samples were obtained 30 min before exercise, immediately after exercise and at 0.5, 1, 2, 4 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-γ (IFN-γ), tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 in samples collected during all three trials, and for IL-1 and IL-10 in samples collected for the CON and EX-bute trials. Data were analysed using ANOVA for repeated measures, and where appropriate, post hoc separation of means utilized the Student–Newman–Keuls test. The null hypothesis was rejected when P P >0.05) in IL-1, IL-6, IFN-γ or TNF-α during CON or following phenylbutazone administration. During the water trial, exercise resulted in significant increases in IFN-γ, IL-1 and TNF-α. It was concluded that high-intensity exercise results in a transient increase in the expression of inflammatory cytokines in blood that is blocked when phenylbutazone is administered to horses.

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.

Clenbuterol is a beta(2)-agonist and potent selective bronchodilator that is used to treat bronchospasm in the horse. The drug is normally administered to horses orally as a syrup formulation. Once absorbed into the systemic circulation, clenbuterol has the potential to cause many side effects, including a repartitioning effect and major alterations in cardiac and skeletal muscle function. Recent studies have also reported that clenbuterol can affect bone and the immune, endocrine and reproductive systems. A great deal of information has been published on the beneficial effects of short term therapeutic doses of clenbuterol on the equine respiratory system, although there is limited information about chronic administration, particularly since this has been associated with adverse physiological effects on other systems. This review summarizes the relevant understanding of clenbuterol for clinicians and horse owners who may administer this drug to pleasure and performance horses.

Methoxy polyethylene glycol–epoetin β (pegylated epoetin β, peg-epoetin β, Mircera®) is an erythropoiesis-stimulating agent that is synthesized by pegylating epoetin β. It is prohibited in racehorses and humans because it enhances their performance. It is detectable in human urine and plasma using the isoelectric focusing–double-blotting (IEF–DB) method that has been widely applied in human doping control laboratories to detect doping with recombinant erythropoietins (EPOs). Fifty micrograms of peg-epoetin β were administered intravenously to a 450 kg female Thoroughbred, and blood was collected for 48 h. The plasma was processed by immunopurification followed by IEF–DB. The analytical procedures required about 2 days. No peg-epoetin β was detected in the baseline plasma collected prior to drug administration. It was readily detected in samples collected at 2, 4, 6, 8, 24 and 48 h. The isoforms showed a characteristic pattern that differed from epoetin β and was unlike any other known erythrocyte-stimulating agent or recombinant EPO. No peg-epoetin β was detected in plasma from five control horses. The plasma samples were also tested by a rapid, automated and chemiluminescent immunometric assay for EPO (Immulite®). The samples collected from the treated horse at 2–48 h contained the equivalent of approximately 200–800 pg ml− 1 of peg-epoetin β. The samples from the ten control horses were negative. These data show that a small dose of peg-epoetin β is detectable for 48 h by two different methods that are based on two different principles (chemiluminescence immunoassay and IEF–DB). The Immulite® assay is suitable as a screen and the IEF–DB assay as a confirmation method. These studies need to be expanded to other horses. The screen and confirmation tests, if applied, will probably eliminate the use of peg-epoetin β as a horse doping agent.

In most mammalian species the developing fetus utilizes large amounts of glutamine derived both from the maternal circulation and synthesized de novo in the placenta. The present study was designed to determine the role of the placenta in glutamine synthesis in the horse. The placentae from eight Standardbred mares were sampled immediately after parturition together with additional tissues obtained at necropsy from three Standbred mares during diestrous. Glutamine synthetase protein was detectable in the non-pregnant horn of the placenta in amounts similar to those seen in gluteus muscle, but the amount in the pregnant horn was two times greater than in the non-pregnant horn. Glutamine was the second most abundant amino acid in amniotic fluid at a concentration of 310 +/- 26 micromole/L with that of glycine being 535 +/- 48 micromole/L. The most abundant amino acids in placental tissue were glycine (3,732 +/- 194 micromole/Kg), glutamate (3,500 +/- 343 micromole/Kg) and glutamine (2,836 +/- 208 micromole/Kg). The results illustrate the importance of glutamine to the equine fetus and establish that the placenta, particularly the pregnant horn, has considerable capacity for glutamine synthesis.

Eight mature (12 +/- 2 yr; MAT) and 5 older (22 +/- 2 yr; OLD) Standardbred mares were used to test the hypothesis that aging and exercise training would alter apoptosis in white blood cells and antioxidant status. The horses were housed indoors overnight (16 h/d) in 3 m x 3 m stalls and were turned out in a drylot during the day. They were fed a diet consisting of total mixed ration, hay cubes fed ad libitum or an equine senior diet plus grass hay. Horses were trained for 20 to 30 min/d, 3 to 5 d/wk for 8 wk at a submaximal work intensity between 60 to 70% of maximal heart rate. A graded exercise test (GXT; stepwise test until exhaustion) was performed before (GXT1) and after (GXT2) the 8 wk of training. During the GXT, blood samples and heart rate were taken at rest, 6 m/s, fatigue, and at 5 and 60 min postfatigue. Fatigue plasma lactate concentration was greater in MAT (19.3 +/- 1.5 at 10 m/s) compared with the OLD (10.9 +/- 1.2 mmol/L at 9 m/s; P = 0.008) horses. There was no effect of age or training on plasma lipid hydroperoxide (LPO) concentration. However, there was a positive correlation between LPO and plasma lactate concentration (r = 0.27, P = 0.006) during acute exercise. There was a greater concentration of total glutathione after GXT1 than after GXT2 (111.8 +/- 5.0 vs. 98.6 +/- 3.4 microM, respectively; P = 0.0002) for both age groups. Apoptosis was less (P = 0.002) in white blood cells of the MAT vs. the OLD group. These results demonstrate that older horses are under similar amounts of oxidative stress, measured by LPO, and have similar levels of glutathione in their systems compared with mature horses. The observation that more glutathione was needed during GXT1 for both groups of horses indicates that training helps horses adapt their system for the intense post-training exercise tests. The greater level of white blood cell apoptosis also indicates that older horses may be immune-compromised during exercise. However, research still needs to be performed regarding dietary supplementation in the aged horse.

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

This study tested the hypothesis that orange peel (O) and decaffeinated black tea (T) extracts would alter markers of exercise performance as well as exercise-induced mRNA expression for the inflammatory cytokines IL-6, TNF-alpha and IFN-gamma. Nine healthy, unfit Standardbred mares (age: 10±4years, ∼450kg) were assigned to three treatment groups in a randomized crossover design where each horse was administered one of the following; placebo (O; 21 water), black tea extract in water (T; 21) or orange peel extract in water (W; 21), via a nasogastric tube. One hour later the horses completed an incremental graded exercise test (GXT) on a treadmill at a fixed 6% grade with measurements and blood samples obtained at rest, at the end of each 1min step of the GXT and at 2 and 5min post-GXT. An additional set of blood samples for Polymerase Chain Reaction (PCR) measurements of mRNA was obtained before exercise and at 5 and 30min and 1, 2, 4 and 24h post-GXT. The GXTs were conducted between 0700 and 1200h not less than 7days apart. There were no differences (P>0.05) in VO2max, respiratory exchange ratio, run time, velocity at VO2max, core body temperature, haematocrit, creatine kinase (CK), plasma lactate concentrations, HR, right ventricular pressure (RVP) or pulmonary artery pressure (PAP) across treatments. A major finding was that orange peel extract significantly reduced post-exercise VO2 recovery time (W = 112±7, O = 86±6, and T = 120±11s). There was a significant difference in plasma total protein concentration (TP) in the O runs compared with water and T. TNF-alpha mRNA expression was lower in the T runs compared with water and O trials. IFN-gamma mRNA expression levels appeared to be lower in both the T and O extract runs compared with the water trials. The mRNA expression of IL-6 was unaltered across treatment groups. These data suggest that orange peel and black tea extracts may modulate the cytokine responses to intense exercise. Orange peel extract reduced post-exercise recovery time and may potentially enhance the ability of horses to perform subsequent bouts of high-intensity exercise.

This study tested the hypothesis that grain and intravenous dextrose challenges would alter plasma concentrations of active ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in Standardbred mares. To deliver 0.5 g of glucose (dextrose solution for the intravenous test)/kg of BW, mares received intravenous dextrose (50% solution) or oral grain administration in 2 trials. In response to the oral grain challenge, plasma glucose and insulin concentrations increased (P < 0.001) by 56 and 802%, respectively. Plasma ghrelin concentration initially decreased (P < 0.001) by 40%, then subsequently increased (P < 0.05) from its nadir by 259%. Plasma leptin concentration decreased (P = 0.002) 17% compared with baseline. There was no change (P = 0.34) in plasma adiponectin concentration in response to oral grain challenge; however, plasma cortisol concentrations decreased (P < 0.001) by 24%. In response to the intravenous dextrose challenge, plasma glucose and insulin concentrations increased (P < 0.001) by 432 and 395%, respectively. Plasma active ghrelin concentration initially decreased (P < 0.001) by 56%, then subsequently increased (P < 0.001) from its nadir by 314%. Plasma leptin concentration also increased (P < 0.001) by 33% compared with baseline. There was no change (P = 0.18) in plasma adiponectin concentration throughout the dextrose challenge. Plasma cortisol concentration increased (P = 0.027) by 20%. Hence, oral grain and intravenous nutrient challenges have the ability to alter variables potentially related to energy metabolism in mares, with acute changes in glucose and insulin possibly modulating changes in ghrelin and leptin.

This study used a randomized crossover design, with investigators blind to the treatment given, to test the hypothesis that seven commercially available electrolyte supplements would alter plasma concentrations of Na+, K+, Cl−, lactate, total protein (TP) and total carbon dioxide (tCO2) as well as plasma strong ion difference (SID) and haematocrit (HCT). Ten unfit Standardbred mares (∼450 kg, 4–9 years) completed a series of simulated race exercise tests (SRT) during which venous blood was collected at five sampling intervals (prior to receiving electrolyte treatment, prior to the SRT, immediately following exercise and at 60 and 90 min post-SRT). Plasma electrolyte and tCO2 concentrations were measured in duplicate using a Beckman EL-ISE electrolyte analyser. No difference (P>0.05) between treatments was detected at any of the five sampling intervals for plasma [Na+], [K+], [Cl−] or [tCO2]. Similarly, no significant difference was detected between treatments across each of the five sampling intervals for plasma SID, HCT or TP concentration. There were differences (P+], [K+] and [tCO2] (as well as plasma SID, HCT, and TP concentration) in the immediately post-SRT samples that were attributable to the physiological pressures associated with acute exercise. No differences (P>0.05) were detected between treatments across the pre-electrolyte and pre-SRT sampling intervals for plasma lactate concentration. There was, however, a significant time by treatment interaction during the 0, 60 and 90 min post-SRT sampling intervals for this parameter. The electrolyte supplements featured in this investigation did not affect either plasma tCO2 concentration or SID; however, this result does not rule out the potential for other supplements, especially those containing alkalinizing ingredients, to exert an effect that could push a horse towards threshold values.

There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4-8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Three MHC isoforms were subsequently identified as type I, type IIA, and type IIX and quantified using a scanning and densometric system. There were no significant differences (p0.05) between old and young mares in fat (%) (19.0+/-6.4 vs 20.5+/-5.4), fat mass (kg) (102.3+/-39.9 vs 106.9+/-37.1), or body weight (kg) (529.4+/-34.9 vs 512.7+/-57.7). However, the old mares had significantly (p0.05) greater lean body mass than the young mares (427.1+/-24.5 vs 405.7+/-37.9). Aged mares had significantly (p0.05) less type I (7.8+/-2.9% vs 12.1+/-4.4%) and IIA (27.8+/-7.1% vs 36.1+/-9.5%) fibres than the young group but more type IIX (64.6+/-4.7% vs 51.8+/-11.1%). The MHC data are consistent with the age-related changes seen in other species.

The purpose of this study was to examine changes in myosin heavy chain (MHC) composition due to chronic clenbuterol administration with or without exercise in mares. Unfit Standardbred mares (aged 10+/-3 years) were divided into four groups: clenbuterol (2.4 micro/kg BW twice daily) plus exercise (3 days/week for 20 min at 50% VO(2max); CLENEX; n=6), clenbuterol only (CLEN; n=6), exercise only (EX; n=5), and control (CON; n=6). Muscle biopsies were obtained from gluteus medius muscle before and after the eight-week training/administration period. MHC composition was determined via SDS gel electrophoresis and quantified using a scanning and densometric system. CLENEX and CLEN exhibited significant (P

Clenbuterol is a β2-adrenoceptor agonist primarily used for treating bronchospasm and alleviating the symptoms of chronic obstructive pulmonary disease (COPD) in the horse. In other species (rats, mice, sheep, and cattle), chronic high doses of clenbuterol (typically in the milligram per kilogram body weight range) has been shown to cause a muscle directed protein anabolic response. Clenbuterol can also modify muscle fibre composition and therefore potentially affect muscle function. This has implications for the performance of exercising horses being treated with therapeutic doses of clenbuterol (typically in the microgram per kilogram body weight range) for bronchospasm or COPD. It is not known whether clenbuterol treatment affects muscle fibre function in horses. The purpose of this study was to examine the effects of a therapeutic dose of clenbuterol, with and without exercise, on the contractile activation characteristics of single membrane permeabilized fibres prepared from muscle biopsies. We tested the hypothesis that therapeutic treatment with clenbuterol would not affect muscle fibre function. Unfit Standardbred mares were treated for 8 weeks with; clenbuterol (2.4 μg/kg twice/day, 5 days/week) plus exercise (20 min at 50% \(\dot V\)O2max 3 d/wk; CLENEX), clenbuterol only (CLEN), or exercise only (EX). Muscle biopsies were taken from the gluteus medius muscle before and after treatment and stored in a glycerol-based solution to prepare permeabilized muscle fibres. The force–pCa relationship for fibres from CLEN horses was steeper (P < 0.05) indicative of greater cooperative interactions within the thin filament, however, fibre sensitivity to Ca2+ was unchanged. In contrast, the steepness of the force–pCa relationship was not changed in fibres from EX and CLENEX horses and Ca2+ sensitivity was also unaffected. Rigor force, activation in the absence of ATP, was not affected by any treatment indicating an approximately equivalent number of participating cross-bridges during activation. The results indicate that a therapeutic dose of clenbuterol to Standardbred horses does not affect the Ca2+-activated contractile characteristics of isolated muscle fibres.

PURPOSE Chronic administration of pharmacological levels of beta2-agonists have been shown to have toxic effects on the heart; however, no data exist on cardiac function after chronic clenbuterol administration. The purpose of this study was to examine the effect of therapeutic levels of clenbuterol on cardiac performance. METHODS Twenty unfit Standardbred mares were divided into four experimental groups: clenbuterol (2.4 microg.kg(-1) twice daily 5 d.wk(-1)) plus exercise (20 min at 50% .VO(2max)) (CLENEX; N = 6), clenbuterol (CLEN; N = 6), exercise (EX; N = 4), and control (CON; N = 4). M-mode and two-dimensional echocardiography (2.5-MHz sector scanner transducer) were used to measure cardiac size and function before and immediately after an incremental exercise test, before and after 8 wk of drug and/or exercise treatments. RESULTS After treatment, CLENEX and CLEN demonstrated significantly higher left ventricular internal dimension (LVD) at end diastole (+23.7 +/- 4.8%; +25.6 +/- 4.1%), LVD at end systole (+29.2 +/- 8.7%; +40.1 +/- 7.9%), interventricular septal wall thickness (IVS) at end diastole (+28.9 +/- 11.0%; +30.7 +/- 7.0%), IVS at end systole (+29.2 +/- 8.7%; +40.1 +/- 7.9%), and left ventricular posterior wall systolic thickness (+43.1 +/- 14.%; +45.8 +/- 14.1%). CLENEX and CLEN had significantly increased aortic root dimensions (+29.9 +/- 6.1%; +24.0 +/- 1.7%), suggesting increased risk of aortic rupture. CONCLUSION Taken together, these data indicate that chronic clenbuterol administration may negatively alter cardiac function.

The purpose of this study was to test the hypothesis that sucralfate, a gastric ulcer medication, would alter plasma concentrations of total carbon dioxide (tCO2), lactate (LA), sodium (Na+), potassium (K+), chloride (Cl-) and total protein (TP), as well as calculated plasma strong ion difference (SID) and packed cell volume (PCV) in horses subjected to a simulated race test (SRT). Six unfit Standardbred mares (approximately 520 kg, 9-18 years) were used in a randomized crossover design with the investigators blinded to the treatment given. The horses were assigned to either a control (40-50 mL apple sauce administered orally (PO)) or a sucralfate (20 mg/kg bodyweight dissolved in 40-50 mL apple sauce administered PO) group. Each horse completed a series of SRTs during which blood samples were taken via jugular venipuncture at five sampling intervals (prior to receiving treatment, prior to SRT, immediately following exercise, and at 60 and 90 min post-SRT). During the SRTs, each horse ran on a treadmill fixed on a 6% grade for 2 min at a warm-up speed (4 m/s) and then for 2 min at a velocity predetermined to produce VO2max. Each horse then walked at 4 m/s for 2 min to complete the SRT. Plasma tCO2, electrolytes, LA, and blood PCV and TP were analysed at all intervals. No differences (P>0.05) were detected between control and sucralfate for any of the measured variables. There were differences (P

Glutamine plays important roles in the interorgan transport of nitrogen, carbon and energy but little is known about glutamine metabolism in the horse. In this study we determined the tissue distribution of glutamine synthetase expression in three Standardbred mares. Expression of glutamine synthetase was highest in kidney and mammary gland, and relatively high in liver and adipose tissue. Expression was lower in gluteus muscle, thymus, colon and lung, and much lower in small intestine, pancreas and uterus. The pattern of glutamine synthetase expression in the horse is similar to that of other herbivores and it is likely that skeletal muscle, liver, adipose tissue and lungs are the major sites of net glutamine synthesis in this species. Expression did not differ between adipose tissue depots but did vary between different muscles. Expression was highest in gluteus and semimembranous muscles and much lower in diaphragm and heart muscles. The concentration of intramuscular free glutamine was inversely correlated with expression of glutamine synthetase ( r = − 0.81, p = 0.0017). The concentration of free glutamine was much higher in heart muscle (21.6 ± 0.9 μmol/g wet wt) than in gluteus muscle (4.19 + 0.33 μmol/g wet wt), which may indicate novel functions and/or regulatory mechanisms for glutamine in the equine heart.

Ageing appears to affect immune and neuroendocirne function in horses and response to acute exercise. No studies have examined the combined effects of training and ageing on immune and neuroendocirne function in horses.To ascertain whether training and age would affect the plasma beta-endorphin (BE) and cortisol (C) as well as immune function responses to acute exercise in Standardbred mares.Graded exercise tests (GXT) and simulated race tests (SRT) were performed before and after 12 weeks training at 60 % HRmax. BE and C were measured at rest and at 5, 10, 20, 40, 60 and 120 min post GXT. Leucocyte cell number, CD4+ and CD8+ lymphocyte subsets, and mitogen stimulated lymphoproliferative response (LPR), were measured in jugular blood before and after the SRTs.Cortisol rose by 5 min post GXT in young (Y) and middle-age (MA) mares (P0.05) and remained elevated until 40 and 60 min post GXT, respectively during both pre- and post training GXT. There was no rise in C in old (0) mares after either GXT (P0.05). Pretraining BE rose (P0.05) by 5 min post GXT in all mares. After training, BE was higher in Y and O vs. MA (P0.05) at 5 min post GXT. Post training BE was higher at 5 min post GXT in Y and O vs. pretraining (P0.05). After SRT, lymphocyte number rose in all mares (P0.05); however, lower lymphocyte numbers (P0.05) were seen in MA vs. Y and O vs. MA (P0.05). The O had reduced LPR to Con A and PHA stimulation (P0.05) compared to Y and MA after the SRT after both pre- and post training SRT. LPR to PWM was lower (P0.05) in O vs. Y and MA after the pretraining SRT. Training caused an increase in resting LPR to PWM in MA only (P0.05).Both age and training altered the plasma beta-endorphin and cortisol responses as well as and immune responses to acute exercise.This study provides important information on the effects of ageing and training that will aid in the management and care of an increasing number of active older horses.

Summary Reasons for performing study:A large percentage of performance horses develop gastric ulcers and many of those horses are treated with omeprazole. Unfortunately, no data have been published on the effects of the drug on markers of performance in animals without ulcers. Hypothesis:Omeprazole would alter markers of aerobic and anaerobic performance. Methods: Ten unfit, healthy, ulcer free, Standardbred mares were administered either control (CON; oral apple sauce, 20 ml) or omeprazole (OP; oral paste, 4 mg/kg bwt s.i.d.) in a random crossover fashion with the investigators blind to the treatment. Treatments were administered for 7 days prior to performing an incremental exercise test (GXT) on a high-speed treadmill. Endoscopic examinations were performed just prior to the trial to verify that the mares were ulcer-free. During the GXT, the mares ran on a treadmill up a 6% grade to measure maximal oxygen consumption (VO2max), run time (RT), velocity at VO2max, maximal velocity (Vmax), packed cell volume (PCV), plasma lactate concentration (LA) and plasma protein concentration (TP). Measurements were recorded at rest, at the end of each 1 min step of the GXT and at 2 and 5 min post GXT. Data were analysed using ANOVA for repeated measures and t tests for paired comparisons. Results: There was no effect (P>0.05) of omeprazole on VO2max; velocity at VO2max; RT; Vmax; 2 min recovery plasma LA. Nor were there any changes (P>0.05) in the relationship between treadmill speed and VO2, PCV, TP, or plasma LA. Conclusions:Omeprazole does not appear to improve physiological markers of performance in healthy, ulcer free horses. Potential relevance:These data may benefit various authorities responsible for deciding administration and timing policies of omeprazole as well as clinicians and horse owners.

Summary Reasons for performing study: Recombinant human erythropoietin (rhuEPO) causes an increase in red blood cell production and aerobic capacity in other species; however, data are lacking on effects in the horse. Hypothesis: This study tested the hypothesis that rhuEPO administration would alter red cell volume (RCV), aerobic capacity (VO2max) and indices of anaerobic power. Methods: Eight healthy, unfit mares accustomed to the laboratory and experimental protocols were randomly assigned to either a control (CON, n=4; 3 ml saline 3 times/week for 3 weeks) or EPO group (EPO, n = 4, 50 iu/kg bwt rhuEPO/3 ml saline 3 times/week for 3 weeks). Exercise tests (GXT) were performed on a treadmill (6% incline), 1 week before and 1 week after treatment. The GXT started at 4 m/sec, with a 1 m/sec increase every 60 sec until the horse reached fatigue. Oxygen uptake was measured via an open flow indirect calorimeter. Blood samples were collected before, during (each step) and 2 and 15 min post GXT to measure packed cell volume (PCV), haemoglobin concentration (Hb), blood lactate concentration (LA) and plasma protein concentration (TP). Plasma volume (PV) was measured using Evans Blue dye. Blood volume (BV) and RCV were calculated using PCV from the 8 m/sec step of the GXT. Results: There were no alterations (P>0.05) in any parameters in CON horses. By week 3, EPO produced increases (P 0.05) due to decreased PV (-11%, P

Concentrations of hormones related to energy homeostasis may differ between populations with varied body compositions, acting as signals to increase or decrease energy intake and/or expenditure. How these parameters correlate with body composition in horses and how they vary in fit (F) versus unfit (UF) Standardbred racehorses is unclear. The purpose of this study was to test the hypothesis that plasma concentrations of glucose (GLU), insulin (INS), cortisol (CORT), ghrelin (GHRL), adiponectin (ADIP) and leptin (LEP) would be correlated with body composition and differ in fit (F) versus unfit (UF) horses. Fasting plasma samples were taken from 12 unfit (11 +/- 2 years, 521 +/- 77 kg; mean +/- SD) and 34 fit (4 +/- 2 years, 475 +/- 83 kg) Standardbred horses. GHRL, LEP, ADIP, INS and CORT concentrations were measured using radioimmunoassay. GLU concentration was measured using colorometric kits. Body composition data included body weight, body condition score (BCS), and percent fat (%fat) calculated using rump fat thickness measured ultrasonically and the Westervelt equation. Data were analyzed using Pearson Product moment and Student's t tests. There were no differences (P0.05) between F and UF horses for the plasma concentrations of CORT (69 +/- 14 versus 76 +/- 23 microg/dL), INS (7.2 +/- 3.5 versus 7.1 +/- 1.8 microIU/mL) or GLU (90 +/- 6 versus 86 +/- 7 mg/dL). Plasma GHRL and ADIP concentrations were greater (P0.05) in F versus UF horses (54 +/- 27 versus 33 +/- 17 pg/mL and 1820 +/- 276 versus 1333 +/- 249 ng/mL, respectively), while plasma LEP was lower in F versus UF (1.0 +/- 0.6 versus 4.4 +/- 2.4 ng/mL, P0.001). BCS and %fat were lower in F versus UF horses (4.8 +/- 0.3 versus 6.7 +/- 0.5 and 11.9 +/- 1.6 versus 15.4 +/- 2.5%, respectively), with no correlation between %fat and GHRL (-0.12, P0.05), although there was a positive correlation between %fat and LEP (+0.72, P0.05), and a negative correlation between %fat and ADIP (-0.40, P0.05). The data show that in comparing fit and unfit horses, there are variations in body composition as well as concurrent and substantial differences in the concentrations of hormones, cytokines, and other parameters related to the control of appetite and feed intake.

Effects of longitudinal exercise training and acute intensive exercise (simulated race test) on immune function have not been reported in horses. Clenbuterol, a beta2-adrenergic agonist, is used to manage inflammatory airway disease in horses. This study investigated the interaction of 8 wk of exercise training with or without 12 wk of clenbuterol administration in horses. Twenty-three untrained standardbred mares (10 +/- 3 yr, Mean +/- SE) were used and divided into four experimental groups. Horses given clenbuterol plus exercise (CLENEX; n = 6) and clenbuterol alone (CLEN; n = 6) received 2.4 microg/kg BW of clenbuterol twice daily (in an average volume of 20 mL) on a schedule of 5 d on and 2 d off for 12 wk. The CLENEX group was also aerobically trained 3 d/wk. Mares given exercise alone (EX; n = 5) were aerobically trained for 3 d/wk, and the control group (CON; n = 6) remained sedentary. Both EX and CON horses were administered similar volumes (approximately 20 mL) of molasses twice daily. A simulated race test (SRT) resulted in an elevation in lymphocyte number postexercise (P < 0.05). There was no significant difference after acute exercise in either monocyte or granulocyte number. Acute exercise resulted in a decrease (P < 0.05) in the percentage of CD4+ and an increase (P < 0.05) in the percentage of CD8+ cells. The SRT resulted in a decreased lymphoproliferative response to pokeweed mitogen (P < 0.05). A SRT had no effect on antibody production in response to equine influenza vaccine. The EX group demonstrated greater cortisol concentrations at rest and at all other time points postexercise after completing the training regimen compared with CLENEX horses (P < 0.05). Preexercise (SRT) peripheral blood monocyte number was lower in CLENEX horses than in other treatment groups (P < 0.05). Clenbuterol and exercise training did not significantly affect post-SRT changes in leukocyte numbers. Exercise training resulted in a decrease (P < 0.05) in the percentage of CD8+ cells post-SRT compared with other groups, but the percentage of CD4+ cells was not altered by either clenbuterol or exercise conditioning. Lymphocyte proliferative response was not affected by clenbuterol or exercise treatment. Horses demonstrated responses to bouts of acute exercise as noted with other species, namely humans and rodents.

Surveys indicate that up to 15% of the equine population in the United States is older than 20 years of age, with many of these animals performing various athletic activities well into their 20s. As is the case with their human counterparts, these geriatric equine athletes have the ability to continue to perform in athletic events. Unfortunately, many horse owners continue to train their active older animals using exercise training protocols that, although appropriate for a younger animal, may not be appropriate for the older equine athlete. Studies in aged human beings have led to a fine-tuning of exercise prescription for the older human athlete so as to prevent the adverse and potentially dangerous effects of excessive work. Published results have led to new and improved programs to promote fitness for the growing population of older adults. Unfortunately, limited data exist regarding the exercise capacity of the aged horse. Future studies on the effects of aging on exercise capacity in equine athletes need to take a few major directions. One question to be answered is at what age does physiologic function first begin to decline in the horse? In human beings, this age varies with training, but noticeable changes in aerobic capacity are first seen in 40- to 50-year-olds. Second, data are needed to determine what levels of exercise enhance the health and well-being of the older horse without harm. Lastly, studies are needed to determine the physiologic mechanisms associated with the onset of aging-induced decreases in physiologic function in the horse. The ultimate goal of all these studies should be to adjust exercise levels to meet the needs of the growing population of athletically active older equine athletes.

The purpose of this study was to test the hypotheses that ageing would result in a decline in maximal heart rate (HRmax) and maximal aerobic capacity (VO2max) and, secondarily, that those effects would be reversible with training. Eighteen, healthy, unfit Standardbred mares representing 3 age groups: young (Y = mean +/- s.e. 6.8 +/- 0.4 years, n = 6); middle-aged (MA = 15.2 +/- 0.4 years, n = 6); and old (O = 27.0 +/- 0.2 years, n = 6) were used. HRmax, VO2max and oxygen pulse at VO2max (OPmax) and the velocities producing HRmax (VHRmax) and VO2max (VVO2max) were measured during pretraining and post-training incremental exercise tests (GXT). During training, mares exercised 3 days/week (Weeks 1-8) and 4 days/week (Weeks 9-12) at a submaximal intensity (approximately 60% HRmax) for approximately 30 min/day. There were no differences (P0.05) between Y and MA, before (218 +/- 2 vs. 213 +/- 3 beats/min; 116 +/- 3 vs. 109 +/- 3 ml/kg bwt/min; 0.55 +/- 0.01 vs. 0.52 +/- 0.02 ml/kg/beat; 9.0 +/- 0.3 vs. 9.3 +/- 0.2 ms; 8.8 +/- 0.2 vs. 8.8 +/- 0.2 m/s) or after training (224 +/- 2 vs. 218 +/- 2 beats/min; 131 +/- 3 vs. 120 +/- 2 ml/kg bwt/min; 0.58 +/- 0.01 vs. 0.55 +/- 0.01 ml/kg/beat; 10.5 +/- 0.2 vs. 9.5 +/- 0.1 ms; 10.6 +/- 0.2 vs. 9.5 +/- 0.1 m/s) for HRmax, VO2max, OPmax, VHRmax or VVO2max, respectively. Old horses had lower HRmax, VO2max and OPmax and reached them at lower velocities compared to Y and MA (P0.05), both before (193 +/- 3 beats/min; 83.2 +/- 2.0 ml/kg bwt/min; 0.43 +/- 0.01 ml/kg/beat; 7.8 +/- 0.1 m/s; 7.2 +/- 0.1 m/s) and after training (198 +/- 2 beats/min; 95 +/- 2 ml/kg bwt/min; 0.48 +/- 0.01 ml/kg/beat; 8.2 +/- 0.2 m/s; 8.0 +/-0.2 m/s). Training did not alter HRmax in any age group (P0.05) but did cause increases in VO2max, OPmax and VVO2max for all groups (P0.05). Interestingly, training increased VHRmax only in Y (P0.05). These data demonstrate that there is a reduction in HRmax, VO2max, OPmax, VHRmax and VVO2max in old horses, and that training can partially reverse some effects of ageing.

This study examined whether body composition was predictive of competitive success in elite standardbreds (STB). Rump fat and muscle thickness (MTH) (vastus lateralis/intermedius [VL], extensor carpi radialis [ECR]) were measured in vivo in male n=6; female n=8 by B-mode ultrasound. Percentage body fat (%fat) was calculated from rump fat. There were no gender differences for age, body mass (males 432+/-11 kg; females 443+/-13 kg), fat-free mass (FFM) (males 400+/-12 kg; females 400+/-11 kg), ECR MTH (males 61+/-2 cm; females 60+/-2 cm) or race time (RT) (males 113+/-3 s; females 114+/-2 s). Males had less (P

Six young (mean + s.e., 5.3 +/- 0.8 years, 445 +/- 13 kg bwt) and 6 old (22.0 +/- 0.4 years, 473 +/- 18 kg bwt) Standardbred and Thoroughbred mares were used to test the hypothesis that age would alter the endocrine response to exercise. All of the mares were unconditioned but accustomed to the laboratory, to standing quietly and running on a treadmill, and to the standardised incremental exercise test (SET) used in the experiment. Two weeks prior to the experiment, each horse underwent a SET to determine maximal oxygen uptake (VO2max) and the speeds to be used in the actual experiment. A second graded exercise test (GXT) was performed without instrumentation for the measurement of plasma renin activity (PRA) and the plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), aldosterone (ALDO), and endothelin-1 (ET-1). Blood samples (30 ml) were collected at rest and at the end of each one minute step of the exercise test. Plasma concentrations of hormones were measured using radioimmunoassay kits. There were no differences (P > 0.05) between old vs. young mares for resting PRA (2.2 +/- 0.3 vs. 1.5 +/- 0.3 ng/ml/h), or the plasma concentrations of ANP (10.0 +/- 0.9 vs. 10.7 +/- 0.6 pg/ml); AVP (0.7 + 0.7 vs. 1.4 +/- 0.4 pg/ml); ALDO (39.2 +/- 10.3 vs. 22.7 +/- 4.6 pg/ml); or ET-1 (0.23 +/- 0.04 vs. 0.18 +/- 0.03 pg/ml). Exercise significantly increased PRA and the concentrations of ANP, AVP, and ALDO in both groups of horses; however, ET-1 was not altered (P > 0.05) by exercise in either group. There were differences (P < 0.05) between means obtained from the old and young groups for PRA (5.4 +/- 0.6 vs. 3.9 +/- 0.8 ng/ml/h and the concentrations of ANP (14.5 +/- 2.3 vs. 26.5 +/- 9.0 pg/ml), AVP (13.6 +/- 0.3 vs. 26.1 +/- 13.9 pg/ml, and ALDO (76.8 +/- 22.0 vs. 41.5 +/- 4.9 pg/ml) measured in samples obtained at the speed eliciting VO2max. These data suggest that older horses have an age-altered endocrine response to exercise.

Summary The purpose of this experiment was to test the hypothesis that chronic (89 days) administration of recombinant equine somatotropin (eST) would increase aerobic capacity and improve exercise performance in old snares. Fifteen, healthy, unfit, aged (20–26 year old) mares were randomly assigned to a treatment (eST, 12.5 sng day−1 in 3 ml glycine/manitol buffer, SC, n=7) or control (vehicle, 3 ml day−1, SC, n=8) group. Aerobic capacity and exercise performance were measured using a standardized exercise test (SET) performed on a high speed treadmill. Tests were conducted before (−21 days), during (+43 days and +89 days) and after (+127 clays) treatment. During the SET, resting data were collected and the horses then ran up a fixed 6% grade, starting at 4 m s−1, with a 1 m s−1 increase every 60 s (omitting 5 m s4) until fatigue. Oxygen uptake (VO2) was measured using an open flow calorimeter and blood lactate concentration (LA) via a lactate analyser. Venous blood samples (10 ml) were collected at rest, during the last 10 s of each step of the SET, and after exercise and used to measure LA, plasma protein concentration (PP), hematocrit (HCT), and the plasma concentrations of creatine kinase (CK) and aspartamine transferase (AST). There were no differences (P>0·05) in resting VO2, LA, TPP, or HCT due to treatment or test time. Furthermore, there were no differences (P>0·05) in maximal oxygen uptake (VO2max), top run velocity, run time, watts at VO2max velocity to produce a lactate of 4 mmoll−1 (VLA4), watts at VLA4, peak HCT or peak LA. Finally, there were no differences (P>0·05) in resting or post-exercise CK or AST. These data indicate that chronic eST administration does not affect aerobic capacity or indices of exercise performance in unfit aged mares.

The purpose of this study was to test the hypothesis that the gastric ulcer medications, ranitidine and omeprazole, would alter plasma concentrations of total carbon dioxide (tCO2), lactate (LA), Na+, K+, Cl− and total protein (TP), as well as calculated plasma strong ion difference (SID) and packed cell volume (PCV) in horses subjected to a simulated race test (SRT). Twelve unfit Standardbred mares (~520 kg, 9–18 years) were used in a randomized crossover design with the investigators blind to the treatment given. Each mare received a treatment three times daily (TID) at 06.30, 12.30 and 18.30 hours. The treatments administered orally were omeprazole (4 mg kg− 1 was given in the morning with apple sauce given at the later, two dosing times to encourage good behaviour), ranitidine (6 mg kg− 1 crushed and mixed in 20 ml apple sauce) and control (20 ml apple sauce TID). Each horse completed a series of SRTs with blood samples taken via jugular venipuncture at five intervals (prior to receiving treatment, prior to SRT, immediately following exercise and at 60 and 90 min post-SRT). During the SRTs, each horse ran on a treadmill fixed on a 6% grade for 2 min at a warm-up speed (4 m s− 1) and then for 2 min at a velocity predetermined to produce VO2max. Each horse then walked at 4 m s− 1 for 2 min to complete the SRT. Plasma tCO2, electrolytes, LA and TP concentrations and PCV–TP were measured in duplicate at all intervals. No differences (P>0.05) were detected between control, ranitidine or omeprazole for any of the measured variables. There were differences (P

This study tested two hypotheses. First, that moderate exercise would alter maternal and foetal heart rate (HR) in the horse. Second, that pregnancy would alter the HR, plasma cortisol and plasma lactate response to moderate exercise in mares. Six unfit, pregnant Standardbred mares (6–19 years) underwent two incremental graded exercise tests (GXT). The first GXT was performed at approximately 9 months of gestation, which represents c. 80% of the total pregnancy time, and the second GXT at approximately 6 months post-parturition. During the GXT, mares ran on a treadmill up a fixed 6% incline completing three 1 min steps at velocities of 4, 6 and 7 m s− 1. Maternal HR was obtained via both electrocardiograph (ECG) and the ventricular waveform obtained from a micromanometer catheter. Data were recorded at rest, at 4, 6 and 7 m s− 1 of the GXT and at 0, 1, 2, 3, 4 and 5 min post-GXT. Foetal HR rate was measured via ECG before, immediately after and at 1, 2, 3, 4 and 5 min post-GXT. Radioimmunoassay (RIA) kits were used to measure plasma cortisol concentration in samples collected before the GXT, immediately after exercise and after 5 min of recovery. Plasma lactate concentrations (LA) were measured at rest, at 4, 6 and 7 m s− 1 and at 5 min post-GXT. Plasma cortisol concentrations were measured using RIA and the samples collected at rest, immediately after and at 5 min post-GXT. Exercise caused no change (P>0.05) in foetal HR. Maternal HR, plasma LA and plasma cortisol concentration were greater (P

Summary Six mature previously inactive horses were utilized for this study. Plasma volume determinations were made under controlled conditions on 2 separate occasions, 7 days apart. A previously published extraction and elution technique was adapted to process the plasma samples containing the Evans Blue dye. Doses of the dye were adapted for use in the horse. The major advantage of this procedure is that it separates the dye from its albumin carrier and removes substances that can interfere with spectrophotometric analysis, causing significant variation. Plasma samples can be run immediately or they can be frozen for several months after collection. There were no significant differences between the mean plasma volumes determined on Day 1 or Day 7. Mean plasma volume for the six horses was 15.7±0.7 liters for the first determination and 16.3±0.9 liters for the second. Average coefficient of variation for the method was 2.6%. In addition to being highly reproducible, this methodology does not require the use of radioisotopes. Finally, the extraction method allows for the use of lower doses of Evans Blue (20 ml of 0.5% aqueous solution) and the dye has a relatively short half-life which allows for repeated measurements of plasma volume.