Reduced high intensity training distance had no effect on VLa4 but attenuated heart rate response in 2-3-year-old Standardbred horses

A metabolomics perspective on 2 years of high-intensity training in horses

The plasma metabolomic profile of elite harness horses subjected to different training programmes was explored. All horses had the same training programme from 1.5 until 2 years of age and then high-intensity training was introduced, with horses divided into high and low training groups. Morning blood samples were collected at 1.5, 2, 2.5 and 3.5 years of age. The plasma was analysed using targeted absolute quantitative analysis and a combination of tandem mass spectrometry, flow-injection analysis and liquid chromatography. Differences between the two training groups were observed at 2 years of age, when 161 metabolites and sums and ratios were lower (e.g. ceramide and several triglycerides) and 51 were higher (e.g. aconitic acid, anserine, sum of PUFA cholesteryl esters and solely ketogenic AAs) in High compared with low horses. The metabolites aconitic acid, anserine, leucine, HArg synthesis and sum of solely ketogenic AAs increased over time, while beta alanine synthesis, ceramides and indole decreased. Therefore high-intensity training promoted adaptations linked to aerobic energy production and amino acid metabolism, and potentially also affected pH-buffering and vascular and insulin responses.

Reduced high-intensity training distance in growing horses had no effect on IGF-1 concentrations, but training onset interrupted time-dependent IGF-1 decline

This study investigated plasma insulin like growth factor (IGF)-1 concentrations in 16 young Standardbred horses introduced to systematic high-intensity training at two different levels of intensity. Growth and locomotion asymmetry and correlations between these and plasma IGF-1 concentrations were also examined. From September as 1-year olds to March as 2-year olds (Period 1), all horses were subjected to the same submaximal training program. In March (start of Period 2), the horses were divided into two groups (n=8) and one group was introduced to regular high-intensity training. The other group was introduced to a program where the high-intensity exercise distances were reduced by 30%. These two training programs were maintained for the remaining 21 months of the study (Periods 2, 3, and 4). There was no effect of training group on plasma IGF-1 concentrations. A continuous decline in IGF-1 levels was observed throughout the study (P<0.0001), with one notable interruption in Period 2 when the IGF-1 concentration remained at the level seen at the start of Period 1. Growth rate of body length was equally high in Periods 1 and 2 (P>0.05). Front and hind limb asymmetry was elevated in Period 2 compared with Period 1. There were positive correlations between IGF-1 concentrations and changes in body condition score, and a negative correlation between IGF-1 concentration and weight. These results indicate that introduction to high-intensity training induces IGF-1 release in horses, but that a 30% difference in the distances used in high-intensity training does not affect IGF-1 levels. The temporary interruption in decline in IGF-1 release with the onset of high-intensity training may influence growth pattern and locomotion asymmetry, but further studies are needed to assess causality.

Locomotion asymmetry in young Standardbred trotters in training and links to future racing career

This study evaluated whether front and hind limb symmetry patterns observed from 1.5 through 3 years of age in Standardbred trotters in training affect racing activity at older age. The hypothesis tested was that asymmetries observed during this period are linked to reduced number of lifetime races and low earnings. Sixteen Standardbreds were subjected to a controlled training and dietary programme from the age of 1.5 years until December as 3-year-olds (P1) and then continued their career with other trainers. On 17 occasions during P1, locomotion asymmetry (vector sum) in front and hind limbs during trot in hand was recorded with a sensor-based system. By 10 years of age, data on lifetime number of races and earnings of the horses were obtained from the Swedish Trotting Association. Horses were divided in groups based on the number of lifetime races performed, i.e. more or less than the median of the cohort born the same year. Mean asymmetry levels did not differ between horses performing more or less lifetime races than the cohort median. However, horses that showed the poorest lifetime race activity showed elevated hind limb asymmetry in August at the age of 3 years, compared to horses with more races (group <median: 9±6 mm vs group >median: 6±2 mm (P=0.02)). There were no correlations between individual mean and peak asymmetries and lifetime earnings. It is concluded that locomotion symmetry observed during trot in hand at the age of 1.5-year-olds to December as 3-year-olds was not a simple and straight-forward predictor of future racing career. However, hind limb asymmetries of around 10 mm in the late season as 3-year-olds could be a warning of impaired future performance.

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.

Effects of Horse Housing System on Energy Balance during Post-Exercise Recovery

Simple Summary

Horse management aims to keep horses healthy and ensure good performance and animal welfare. Many horses are currently kept in individual box stalls indoors, a housing system that limits free movement, exploration, and social interaction, and may also subject horses to lower air quality. The alternative is a free-range housing system where horses are kept in groups outdoors. Anecdotal information indicates concerns among sports horse trainers that lack of rest in such systems delays recovery and impairs performance. This study examined whether recovery after competition-like exercise in Standardbred trotters was affected by housing system. The results showed that a free-range housing system did not delay recovery in Standardbred trotters, and in fact had positive effects on appetite and recovery of energy balance.

Abstract

This study examined the effects of two housing systems (free-range and box stalls) on recovery of energy balance after competition-like exercise in Standardbred horses. Eight adult geldings (mean age 11 years) were used. The study had a change-over design, with the box stall (BOX) and free-range group housing (FreeR) treatments each run for 21 days. The horses were fed forage ad libitum and performed two similar race-like exercise tests (ET), on day 7 and day 14 in each treatment. Forage intake was recorded during the last 6–7 days in each period. Blood samples were collected before, during, and until 44 h after ET. Voluntary forage intake (measured in groups with four horses in each group) was higher in FreeR horses than BOX horses (FreeR: 48, BOX: 39, standard error of the mean (SEM) 1.7 kg (p = 0.003)). Plasma non-esterified fatty acids (NEFA) was lower at 20–44 h of recovery than before in FreeR horses (p = 0.022), but not in BOX horses. Housing did not affect exercise heart rate, plasma lactate, plasma urea, or total plasma protein concentration. Thus the free-range housing system hastened recovery in Standardbred trotters, contradicting anecdotal claims that it delays recovery. The free-range housing also had positive effects on appetite and recovery of energy balance.

Diurnal rhythms of heart and respiratory rates in donkeys of different age groups during the cold-dry and hot-dry seasons in a tropical savannah

The aim of this study was to determine the effect of season on diurnal rhythms of heart (HR) and respiratory rates (RespR) in the adult, yearling, and foal donkeys during the cold-dry and hot-dry seasons under natural light/dark cycle. The resting HR and RespR were recorded bihourly for 24 consecutive hours from 06:00 to 06:00 h (GMT +1) in 30, clinically healthy donkeys (10 adults,10 yearlings, and 10 foals). Dry-bulb temperature (DBT), relative humidity (RH), temperature-humidity index (THI) and wet-bulb globe temperature index (WBGT) inside the pen were recorded bihourly from 06:00 to 06:00 h. Values of DBT, THI, and WBGT obtained during the hot-dry season were significantly (P < 0.05) higher than corresponding values recorded during the cold-dry season. Application of single-cosinor procedure showed that HR and RespR exhibited daily rhythmicity in both seasons. The mesors of the HR in adult (41.51 ± 0.34 beats/min [bpm]), yearling (40.80 ± 0.43 bpm), and foal (47.55 ± 0.40 bpm) donkeys during the cold-dry season were significantly (P < 0.01) lower, compared to the corresponding values of 48.4 ± 0.40 bpm, 50.42 ± 0.52 bpm and 58.10 ± 0.50 bpm, respectively during the hot-dry season. The mesors of RespR in adult, yearling, and foal donkeys during the hot-dry season were higher (P < 0.05), when compared to the corresponding values recorded in the cold-dry season. The HR and RespR of foals were significantly (P < 0.05) higher than those of the adult and yearling donkeys. Amplitudes of HR and RespR were higher during the hot-dry season than the cold-dry season. In conclusion, seasonal changes affect diurnal rhythmicity of HR and RespR of adult, yearling, and foal donkeys during the cold-dry and hot-dry seasons. The HR and RespR of donkeys vary with age, with higher values in the foals than the adult and yearling donkeys in both seasons.

Physiological response to an experimental 100 m flying pace race in Icelandic horses and effect of rider

This study evaluated the physiological response to an experimental 100 m flying pace race (EPR) in Icelandic horses with pace-competition experience, and whether there was an effect of rider. A cross-over design with nine horses and two riders was used. The EPR was performed twice (once with each rider) with four days of rest in-between. The EPR consisted of two runs (I and II), of which at least 100 m was in pace at full speed according to international competition rules. Plasma lactate concentration increased and was greater after pace run II than I (18.5±1.3 vs 11.9±0.7 mmol/l; P<0.001). Heart rate was higher during pace run I than II (207±3 vs 205±3; P=0.02). Heart rate and Lact had not recovered 30 min post exercise but Hct was back to resting level after 30 min recovery. Speed did not differ between riders and pace runs (pooled mean ± standard deviation of pace runs: 10.4±0.7 m/s, range 9.2-12.1 m/s) but HR and Lact were higher from warm-up and until 30 min recovery with rider 1 than 2 (P<0.001). There was a negative correlation between post EPR Lact with rider 1 and previous best record (r2=0.72, P=0.032). To conclude, a 100 m flying pace race in the Icelandic horse is a high-intensity exercise and anaerobic metabolism is crucial for performance. The rider had an effect on the physiological response but it is unclear if it was due to body weight, riding style or both. The practical relevance of the differences observed between riders remains to be proven but our results indicate that they may have limited impact on single day competitions since the speed was the same with the two riders.

Reduced training distance and a forage-only diet did not limit race participation in young Standardbred horses

In this study, a survey was used to document the type and amount of training to which 2- to 3-year old Swedish Standardbred horses are generally subjected. Moreover, an experimental study was conducted to examine the ability to achieve conventional performance goals in 16 Standardbred geldings fed a forage-only diet and allocated to either a control training programme (C-group) or a training programme with the high intensity training distance reduced by 30% (R-group) from March as 2-year-olds until December as 3-year-olds. The median distance of high intensity training per week reported by professional trainers was 6,700 m. In experimental horses, planned high intensity training/week was 6,315 and 4,288 m in C-group and R-group, respectively. There was no difference between experimental training groups in ability to race. The proportion of experimental horses that passed a preparation race as 2-year-olds (100%) and qualified for races (94%) was greater (P<0.05) than for the rest of the cohort (77 and 63%), geldings of the same cohort (71 and 45%) and siblings of the experimental horses (84 and 69%). The proportion of horses that raced (56%) was equal to that of the cohort and of siblings (54%), but greater than the proportion of cohort geldings (35%, P<0.05). In experimental horses, total earnings until 7 years of age were correlated to exercise haematocrit as 3-year-olds (r=0.51, P>0.05) and number of races (r=0.55, P>0.05). Race record was correlated to VLa4 as 3-year-olds (r=-0.75, P<0.01). It was concluded that a forage-only diet and shorter distance of high intensity training than commonly used in Standardbred training in Sweden do not appear to restrict ability to qualify for races and race before 4 years of age.

Effects of training distance on feed intake, growth, body condition and muscle glycogen content in young Standardbred horses fed a forage-only diet

This study examined feed intake, growth, body condition, muscle glycogen content and nutrition-related health in 16 Standardbred horses fed a high-energy, forage-only diet ad libitum and allocated to either a control training programme (C-group) or a training programme with the high-intensity training distance reduced by 30% (R-group), from January as 2-year olds until December as 3-year olds. Feed intake was recorded on 10 occasions during 3 consecutive days. Body weight was recorded once in a week and height, body condition score (BCS), rump fat thickness and thickness of the m. longissimus dorsi were measured at 7±3-week intervals throughout the study. Muscle biopsies of the m. gluteus medius were taken in December as 2-year olds and in November as 3-year olds and analysed for glycogen content. Nutrition-related health disorders were noted when they occurred. Horses consumed 1.7% to 2.6% dry matter of BW, corresponding to 19 to 28 MJ metabolisable energy/100 kg BW. There were no differences between training groups in feed intake or any of the body measurements. The pooled weekly BCS was maintained between 4.8 and 5.1 (root mean square error (RMSE)=0.4). Muscle glycogen content was 587 and 623 mmol/kg dry weight (RMSE=68) as 2- and 3-year olds, respectively, and there was no difference between training groups. When managed under normal conditions, no nutrition-related health disorders or stereotypic behaviours were observed. It was concluded that the training programme did not affect feed intake, growth, BCS or muscle glycogen content. In addition, the forage-only diet did not appear to prohibit muscle glycogen storage, growth or maintenance of body condition, and seemed to promote good nutrition-related health.

The effect of rider weight and additional weight in Icelandic horses in tölt: part I. Physiological responses

This study examined the effect of increasing BW ratio (BWR) between rider and horse, in the BWR range common for Icelandic horses (20% to 35%), on heart rate (HR), plasma lactate concentration (Lac), BWR at Lac 4 mmol/l (W₄), breathing frequency (BF), rectal temperature (RT) and hematocrit (Hct) in Icelandic horses. In total, eight experienced school-horses were used in an incremental exercise test performed outdoors on an oval riding track and one rider rode all horses. The exercise test consisted of five phases (each 642 m) in tölt, a four-beat symmetrical gait, at a speed of 5.4±0.1 m/s (mean±SD), where BWR between rider (including saddle) and horse started at 20% (BWR₂₀), was increased to 25% (BWR₂₅), 30% (BWR₃₀), and 35% (BWR₃₅) and finally decreased to 20% (BWR_20b). Between phases, the horses were stopped (~5.5 min) to add lead weights to specially adjusted saddle bags and a vest on the rider. Heart rate was measured during warm-up, the exercise test and after 5, 15 and 30 min of recovery and blood samples were taken and BF recorded at rest, and at end of each of these aforementioned occasions. Rectal temperature was measured at rest, at end of the exercise test and after a 30-min recovery period. Body size and body condition score (BCS) were registered and a clinical examination performed on the day before the test and for 2 days after. Heart rate and BF increased linearly (P<0.05) and Lac exponentially (P<0.05) with increasing BWR. The W₄ was 22.7±4.3% (individual range 17.0% to 27.5%). There was a positive correlation between back BCS and W₄ (r=0.75; P=0.032), but no other correlations between body measurements and W₄ were found. Hematocrit was not affected by BWR (P>0.05), but negative correlations (P<0.05) existed between body size measurements and Hct. While HR, Hct and BF recovered to values at rest within 30 min, Lac and RT did not. All horses had no clinical remarks on palpation and at walk 1 and 2 days after the test. In conclusion, increasing BWR from 20% to 35% resulted in increased HR, Lac, RT and BF responses in the test group of experienced adult Icelandic riding horses. The horses mainly worked aerobically until BWR reached 22.7%, but considerable individual differences (17.0% to 27.5%) existed that were not linked to horse size, but to back BCS.

Lactate-guided conditioning program using variable exercise intensities improves fitness and alters muscle enzyme activity but not inflammatory response in horses

Blood lactate concentration ([LA]) response to exercise challenges can be used to assess fitness in horses. Most equine conditioning programs (CP) that have been studied are based on regular bouts of exercise of similar to increasing levels of intensity. We hypothesised that a lactate-guided CP implementing 2× weekly short-duration high-intensity exercise bouts and 1× weekly low-intensity longer-duration exercise bout effectively increases fitness in horses. Six untrained adult horses followed a 12 week CP that consisted of 2× weekly exercise on an equine treadmill (6% incline) for 25 min at a velocity at which [LA] was 4.0 mmol/l (VLA4.0) and 1× weekly for 45 min at a velocity at which [LA] was 2.5 mmol/l (VLA2.5). VLA2.5 and VLA4.0 were determined by incremental-step standardised-exercisetest (SET) before the CP and adjusted every 3 weeks. Blood was collected for [LA], creatine kinase (CK), aspartate aminotransferase (AST), serum amyloid A (SAA), and fibrinogen (Fb) before each speed increase and 30 min, 2, 4, and 24 h after termination of the SET, when [LA] was ≥4.0 mmol/l. Repeated-measures ANOVA was used for analysis. During each SET horses showed increases in heart rate (P<0.0001), packed cell volume (P=0.003), and [LA] (P=0.002). Throughout the CP, VLA2.5 increased from 5.6±0.2 to 6.7±0.3 m/s (P<0.05) and VLA4.0 increased from 6.0±0.2 to 7.4±0.3 m/s (P<0.01). CK, AST, SAA, and Fb did not increase following submaximal exercise. CK and AST activity were attenuated throughout the 12 week CP (P<0.05). This lactate-guided CP was effective at increasing fitness based on achieving higher speeds during the SETs and did not appear to have deleterious effects on the horses’ muscular system or inflammatory state.

Mitochondrial function and aerobic capacity assessed by high resolution respirometry in Thoroughbred horses

During the initial stages of training of young Thoroughbred horses, low intensity exercise is employed to increase aerobic capacity. High Resolution Respirometry (HRR) allows the determination of aerobic capacities in small samples of permeabilised muscle fibres. The aim of the study was to measure the mitochondrial function by HRR in Thoroughbred horses, to compare these values to Warmblood horses and to evaluate the effect of a 10-weeks training period. The mitochondrial function was measured by HRR using different substrate-uncoupler protocols (SUIT 1 and 2) in muscle microbiopsies from two groups of untrained horses: 17 Warmblood and 8 Thoroughbred and in the group of 8 Thoroughbred horses before and after a 10-week training period. The SUIT1 protocol employed to compare the two groups of horses showed that in Thoroughbred horses, the mean values for oxygen flux expressed as tissue mass-specific respiration were significantly higher for complex I (CI)Glutamate+Malate, CI + complex II, and maximum electron transport capacities (ETSmax) than the mean values measured in Warmblood horses. The SUIT 1 and SUIT 2 protocols revealed large differences among Thoroughbred horses before and after training. The SUIT 2 protocols showed a significant difference for the complex I activity before and after training but only when the oxygen flux was expressed as percentage of ETSmax. This study shows the interest of HRR in equine sport medicine and exercise physiology, but shows that the technique requires further refinement. Indeed significant differences have been shown between the Thoroughbred and the Warmblood horses highlighting the need to have baseline data for each breed. The Thoroughbred horses had globally a high oxidative phosphorylation capacity with an increase of CI activity induced by an aerobic training program.