Effects of Standardized Exercise Tests on Plasma Thyroid Hormones' Kinetics in Standardbred Racehorses.

This study examined how a standard exercise test (SET) affected (1) thyroid hormones (THs) of horses and (2) the relationship between the VLa4 of horses and TH responses to the exercise in trained Standardbred racehorses (VLa4 is the velocity run at defined conditions at which a blood lactate concentration of 4 mmol/L is determined). Twelve trained Standardbred racehorses (six stallions and six mares) performed SETs until the horses' blood lactate concentration was at or above 4 mmol/L. The horses were divided into three age groups (2, 3, and 4 years old); each group consists of 4 horses respectively (two male and two female), to evaluate the effects of age and sex on hormonal responses to SET. During each SET, blood samples were taken at rest and after each interval and at the end of SET. Blood was analysed for total and free triiodothyronine (T3, fT3) as well as total and free thyroxine (T4, fT4). The statistical model included three fixed factors (SET, sex and age) and their main interactions. ANOVA analysis revealed that T3 and fT3 were significantly influenced by SETs. Plasma T3 and fT3 concentrations were higher in 4-year-old horses compared to the other age groups. All plasma THs concentrations were higher in mares than in stallions. Correlations revealed that a higher VLa4 was negatively related to all THs responses in 2-year-old Standardbred mares only. The SET used to determine VLa4 increased selected THs (T3, fT3); these increases were inversely related to VLa4 and affected by age and sex of the horses. The correlation of VLa4 with thyroid exercise' response might provide some additional information for performance evaluation of Standardbred racehorses, especially for evaluating training adaptation, according to sex, and age. Further studies are necessary to provide support on the value of measuring THs in Standardbred racehorses of different sex and age.

Measurement of Endurance of Untrained Five-Year-Old and Six-Year-Old Horses Raised in Multi-age Herds on Pasture.

The objective of this study was to explore how the endurance of five-year-old horses, kept out on pasture all their life and ridden for the first time well into their fifth year of age, developed within one year and compared to that of six-year-old horses raised under the same conditions and to other horses. Horses were submitted to a standardized exercise test (SET) to calculate their v4 (velocity run under defined conditions inducing 4 mmol/L of blood lactate concentration (LA)) and v180 (velocity run under defined conditions inducing a heart rate of 180 beats/min). The test consisted of up to five consecutive intervals at increasing speed until the blood LA of a horse increased above 4 mmol/L. The blood LA measured after each interval was plotted exponentially against running speed to derive v4 from the blood lactate-running speed relationship, and the mean heart rate during the intervals was plotted linearly against running speed to derive v180 from the heart rate-running speed relationship. The following were examined: (1) the development of v4 and v180 of five-year-old horses within one year through measurements in September and in the following July and September; the comparison of endurance variables (2) between five-year-olds and six-year-olds; (3) between six-year-olds on consecutive years; and 4) between six-year-olds and foreign horses. The results showed that: (1) there were no changes of either variable within one year (repeated measures ANOVA P > .05); (2) there were no significant differences between five-year-olds and six-year-olds (one-way ANOVA P > .05); (3) no significant differences between six-year-old groups (one-way ANOVA; P > 05); and (4) foreign horses had higher v4 and v180 values than six-year-olds (one-way ANOVA; P = .0001 and P = .003, respectively). There was no significant relationship between v4 and v180 (P > .05; r2 = 0.02). In conclusion, one additional year on pasture in multiage herds did not increase the endurance variables of five-year-old horses. Thus, the endurance appeared to be consolidated in these horses at the age of five years, and additional training seems to be necessary to increase it.

Relationship between Resting and Recovery Heart Rate in Horses.

In endurance racing the heart rate (HR) of horses in the veterinary gates has to reach a maximum set to continue racing. There is no literature on the relationship between resting HR (HRresting) and HR after exercise (HRrecovery). This relationship was examined in seven horses and the results were related to their v4 (speed at which the blood lactate concentration is 4 mmol/L). Horses were submitted to an exercise test to determine v4. Thereafter, horses were exercised on a treadmill in randomized order for 10 and 60 min at different speeds. HR was measured before exercise and several times until 30 min of recovery. The relationship between HRresting and HRrecovery was significant in 16 out of 35 comparisons. There were no significant relationships between the v4 of the horses and their HRresting and between v4 and HRrecovery after 10 min of exercise, regardless of the speed of exercise, with one exception. The relationship between the v4 of the horses and their HRrecovery after 60 min of exercise was significant in the fifth minute after exercise at 3.5 m/s only. Conclusion: Because HRresting and HRrecovery are often related, pre-determined arbitrary HRrecovery values may not allow for fair competition during endurance racing.

Global Positioning System-Determined and Stopwatch-Determined Running Speeds of Horses Differ.

Global positioning systems (GPS) have become very popular tools to determine the running speed of horses. However, information on the accuracy of these measurements is scarce. The objective of this study was to examine the accuracy of speed determinations using GPS. For this purpose, the running speeds determined using the GPS of the Polar M400 Equine heart rate meter (G-speed) and a stopwatch (W-speed; manual division of the measured time over the distance run) were compared. The hypothesis was that the speeds determined by both methods would be the same. Eleven horses ran a standardized exercise test (SET) with 130 m laps, and 8 horses ran a SET with 250 m laps in two different sandy riding arenas (one was indoor). The length of the laps was determined with a distance measuring wheel and marked with red traffic cones for the riders to maintain an accurate course. The SETs consisted of five intervals at increasing speeds each. The duration of the intervals was between 3 and 6 minutes. Horses ran a defined number of laps in each interval to reach the prescribed durations. Data were analyzed using a paired Student's t-test; P < .05 denoted significance. W-speeds differed from G-speeds for all intervals in both riding arenas (P between .01 and .001). G-speed was lower for each interval. With increasing speed, the difference between the two methods augmented. The hypothesis was rejected, therefore questioning the accuracy of the Polar M400 in determining speed under the conditions of this study.

Effect of racing on blood variables in Standardbred horses.

BACKGROUND: Blood is collected for hematologic and biochemical analyses when racehorses perform poorly. However, racing affects most analyte levels; therefore, the timing of blood sampling can affect analyte levels and interpretations. OBJECTIVE: This study aimed to determine if the blood variable levels returned to pre-racing levels 2 and 3 days post-racing. METHODS: Blood was sampled from 17 healthy racehorses pre- and post-racing. The variables measured from plasma were albumin, cholesterol, creatinine, calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na), potassium (K), creatine phosphokinase (CK), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT), and cortisol. Hematocrit (HCT), hemoglobin (HGB), white blood cell (WBC), red blood cell (RBC), granulocyte, and lymphocyte counts were analyzed from blood collected in EDTA-coated vials. RESULTS: Calcium was lower 3 days post-racing compared with 2 days pre-racing (P < 0.01), P and GGT were higher 2 and 3 days post-racing compared with those at the pre-racing timepoints (P ≤ 0.01), and RBC, HCT, and HGB were higher 2 days post-racing compared with those at the pre-racing and 3-day post-racing time points (P < 0.01, all). CONCLUSIONS: A few blood biochemical and hematologic variables were significantly altered 2 and 3 days post-racing. The level of these changes did not affect the clinicopathologic interpretation of the values.

Transient increase with strenuous exercise of plasma levels of glycosaminoglycans in humans and horses.

Plasma glycosaminoglycans (GAGs) were isolated and purified by chromatographic procedures in healthy humans and horses before and after physical exercise. A weak anion exchange resin was used to separate polyanions. Humans exercised on a cycloergometer, while horses were exercised on a treadmill and in show jumping competition. Some GAGs were isolated from untreated plasma and operationally defined as native proteoglycans (PGs), while the total GAG amount was isolated from mild alkali treated plasma. Plasma GAG concentrations in terms of galactosamine and galactose, the respective components of the cartilage polysaccharides chondroitin sulphate and keratan sulphate, significantly increased only when the subject was exercised intensively, in both humans and horses. Only native PGs fraction contributed to GAG levels changes. The increases were transient, since preexercise values were reached in 30 min in horses. These changes with exercise are suggested to be a tool to measure the effect of physical exercise on cartilage PG metabolism.

Effects of intensity and duration of exercise on muscular responses to training of thoroughbred racehorses.

This study examined the effects of the intensity and duration of exercise on the nature and magnitude of training adaptations in muscle of adolescent (2-3 yr old) racehorses. Six thoroughbreds that had been pretrained for 2 mo performed six consecutive conditioning programs of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 2.5 mmol/l (v2.5) and 4 mmol/l (v4), respectively] and durations (5, 15, 25 min). Pre- and posttraining gluteus muscle biopsies were analyzed for myosin heavy chain content, fiber-type composition, fiber size, capillarization, and fiber histochemical oxidative and glycolytic capabilities. Although training adaptations were similar in nature, they varied greatly in magnitude among the different training protocols. Overall, the use of v4 as the exercise intensity for 25 min elicited the most consistent training adaptations in muscle, whereas the minimal training stimulus that evoked any significant change was identified with exercises of 15 min at v2.5. Within this range, muscular adaptations showed significant trends to be proportional to the exercise load of specific training programs. Taken together, these data suggest that muscular adaptations to training in horses occur on a continuum that is based on the exercise intensity and duration of training. The practical implications of this study are that exercises for 15 to 25 min/day at velocities between v2.5 and v4 can improve in the short term (3 wk) the muscular stamina in thoroughbreds. However, exercises of 5-15 min at v4 are necessary to enhance muscular features related to strength (hypertrophy).