Inheritance of racing performance of Thoroughbred horses

Horse racing is a contest between horses, usually held for the purpose of betting. Thoroughbred horse racing is the most diffused form of horse racing throughout the world. Thoroughbred is one of the most versatile of horse breeds and has influenced the development of many other breeds. Thoroughbred horses served as a foundation stock for the development of the light horse breeds. The two types of horse racing are flat racing and jumping races/steeplechases. The measures of racing performance are broadly classified into three categories. They are time and its several variations, handicap or similar performance ratings and earnings. One common measure of the performance of racehorses evaluated genetically is racing time or final time. The heritability estimates differed according to method of estimation, age, sex, track and distance. Time measure generally had a heritability in the range of 0.1 to 0.2 with the higher values for shorter races. For handicap and earning measures the heritabilities reported were generally higher in the range of 0.3 to 0.4; hence these may be considered in genetic evaluation of racing performance of Thoroughbred horses. The average generation interval of Thoroughbred horses was 11.2 ± 4.5 and 9.7 ± 3.8 years for males and females respectively, which limits the genetic progress in racing horses. However, the major advantage is that the racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal in relatively short periods. These factors coupled with the reasonable heritability of some measures of racing performance, suggest that mass selection based on performance tests would be the selection procedure of choice to improve the racing performance of Thoroughbred horses. In general, the inbreeding at the rate that is usually practised in Thoroughbred population does not enable much gene fixing. However, practice of close inbreeding may be avoided, even though it still fascinates breeders at subconscious level.     

Biomechanics in young and adult italian standardbred trotter horses in real racing conditions

This study was undertaken to characterize and establish the kinematic standards of Italian standardbred trotter horses in real racing conditions. Certain parameters, such as the angles of both front and hind fetlock joints, stride length, stride frequency and average speed in youngs and adults are presented, examinated and compared with statistical tests. The angles and stride length were obtained using ONTRACK software over frames extracted from two CANON MV630i digital videocameras. For the stride frequency, a third identical videocamera filmed the horses to count the number of beats per minute. The average speed was calculated by multiplying the stride frequency by the stride length and transforming the result into kilometers per hour. The data reveal that as speed increases, younger horses have more extended fetlock joints than adults. Contrary to this, at the maximum speed (hereafter referred to as sprint speed) the adults increase both their stride frequency and stride length, while young horses increase stride frequency and decrease stride length. We think that the knowledge of these parameters in competition breeds could have potential relevance as they may reveal early indicators of the development of proper and adequate characteristics in young horses of those breeds.     

Postoperative performance of racing horses with tearing of the medial palmar intercarpal ligament

OBJECTIVE: To examine the relationship between medial palmar intercarpal ligament (MPICL) tearing and postoperative performance in racing horses. MATERIALS AND METHODS: The postoperative performance of 42 horses in which the midcarpal joint was examined arthroscopically was followed prospectively. Intra-articular variables examined were the severity of MPICL tearing, subchondral bone damage and articular cartilage damage. Using a scoring system based on the class of race and the position in the race, a mean score was calculated for up to five races before and after surgery. The preoperative score was subtracted from the postoperative score to give a net score. Statistical analysis was by a Mann Whitney U test and multiple linear regression. RESULTS: Thirty-two (76%) raced postoperatively, 23 (55%) won at least one race and 12 of 26 (46%) performed at the same or higher level. Horses with grades 2 to 4 MPICL tearing had significantly lower net scores than those with grade 1 or no tearing. The severity of subchondral bone damage was the only variable on its own that was significantly correlated with net score (r2 = 0.23, P < 0.05). The addition of the grade of MPICL tearing to bone damage significantly improved the prediction of postoperative performance (P < 0.05). The inclusion of articular cartilage damage had no effect on the prediction of postoperative performance. CONCLUSION: Tears involving more than one third of the MPICL as observed arthroscopically have a significant detrimental affect on postoperative performance of racing horses.     

Biokinematics under Competitive Racing Conditions in Young Standardbred Trotters: A Preliminary Report

With the aim of evaluating equine performance in competitive trotter horses under normal racing conditions data of stride length, stride frequency and mean horses speed were obtained from 50, 2-year-old Italian winner fillies during the racing and the sprint laps of competition. The enhancement of speed in the sprint lap was obtained by increasing both stride length and stride frequency. Stride frequency for the racing and the sprint laps were (mean ± SD) 133.63 ± 3.93 and 138.97 ± 6.62 strides per minute, respectively and Stride length for the racing and the sprint laps were 7.17 ± 0.17 and 7.30 ± 0.11 m, respectively; mean speed was 48.18 ± 1.09 km/hr. The usefulness of the kinematic assessments is discussed as is its potential reference for future indicators of performance.     

Biokinematics Under Competitive Racing Conditions in Young Standardbred Trotter Horses: A Preliminary Report

The aim of this study was to evaluate equine performance in competitive trotter horses under normal racing conditions. Data of stride length, stride frequency, and mean horse speed were obtained from 50 2-year-old Italian fillies that were winners during the racing and the sprint laps of competition. The enhancement of speed in the sprint lap was obtained by increasing both stride length and stride frequency. Stride frequencies for the racing and the sprint laps were (mean ± SD) 133.63 ± 3.93 and 138.97 ± 6.62 strides per minute, respectively, and stride lengths for the racing and the sprint laps were 7.17 ± 0.17 and 7.30 ± 0.11 m, respectively; mean speed was 48.18 ± 1.09. The usefulness of the kinematic assessments as well as its potential reference for future indicators of performance is discussed in this study.     

Genetic correlations between performance at different racing distances in Thoroughbreds

The aim of the present study was to estimate genetic correlations between time at different racing distances in Thoroughbred racehorses based on data provided by Turftotal Ltda. The traits evaluated were times in seconds for distances of 1000, 1100, 1200, 1300, 1400, 1500 and 1600 m, with a total of 32,145 races and 238,890 time records being analyzed. The (co)variance components necessary to obtain the genetic correlations were estimated using the MTGSAM program in a two-trait animal model. The model used for analysis of the data involved animal and permanent environmental random effects, and race, sex, age and post position at start as fixed effects. All genetic correlations were positive and ranged from medium (0.54) to high (0.93).     

A longitudinal study of racing thoroughbreds: performance during the first years of racing

OBJECTIVES: To develop a profile of the racing careers of Thoroughbred horses in south-eastern Queensland, and to examine factors that affect racing during the first years of racing. DESIGN AND PROCEDURE: A longitudinal study using the racing records of a defined cohort of Thoroughbred horses that were born on or within 12 months following 1 August 1991. Data collection commenced in 1996 and will continue until all horses cease racing. In this paper two measures of performance were examined: race earnings during the first year of racing and cumulative proportion of horses still racing up to 2 years after their first start. Univariable and multivariable methods were used to describe and identify factors associated with the performance of these horses. RESULTS: By 31 July 1997, 1804 horses were enrolled in the study including 916, 701, 152 and 35 horses that first raced at 2, 3, 4 and 5 years of age, respectively. During their first year of racing, half the horses earned no more than A$450 from race earnings, and 710 (39.4%) horses earned no money at all. In comparison to poorly performing horses, well-performing horses were more likely to be male, to have started as 2-year-olds and to have had more starts during this year. Of the horses that first started as 2 and 3-year-olds, only 71 and 46% continued racing for at least 1 and 2 years after their first start, respectively. Length of racing life was associated with performance during the first year of racing (number of starts and average earnings per race), and with sex, date of birth and age at first start. CONCLUSIONS: The study confirmed a high wastage among racing Thoroughbreds. As expected, premature retirement from racing was linked to poor performance. During the first year of racing, the race earnings of an estimated 1567 (86.9%) horses were insufficient to cover training costs. The 2-year-old racing cohort outperformed the older racing cohorts in each of the performance measures under investigation. Interpretation of this result, and the long-term effects of 2-year-old racing, was limited by the problem of confounding.     

Resting concentrations of cardiac troponin I in fit horses and effect of racing

ObjectivesTo determine normal resting values for cardiac troponin I (cTnI) in healthy Standardbred, Thoroughbred and Warmblood horses and investigate if racing has an influence on cTnI concentrations.BackgroundMeasuring cTnI concentrations in plasma is the gold standard for detecting myocardial injury in humans. Cardiac troponin I is highly conserved between species and has gained interest as a marker for cardiac injury in horses. Increased levels of cTnI have been reported in association with endurance and short-term strenuous exercise on a treadmill in horses. However, the effect of true racing conditions has not yet been reported.Animals, materials and methodsBlood samples for analysis of cTnI concentrations in plasma were collected from 67 Standardbred racehorses, 34 Thoroughbred racehorses and 35 Warmblood dressage horses at rest. Blood samples were also collected prior to and after racing in 22 Standardbred racehorses and 6 Thoroughbred racehorses.ResultsAll horses except one had resting plasma cTnI concentrations <0.022 μg/L. Mild increases in cTnI concentrations were seen in some horses 1–2 h after the race (1/17 Standardbreds and 2/6 Thoroughbreds) as well as 10–14 h after the race (4/21 Standardbreds and 1/6 Thoroughbreds).ConclusionsResting cTnI concentrations in horses are low but mildly elevated cTnI concentrations may be detected in some horses 1–14 h after racing. These findings could be of importance when evaluating horses with suspected cardiac disease that recently have performed hard exercise.     

Inheritance of equine sarcoid disease in Franches-Montagnes horses

The mode of inheritance for susceptibility to equine sarcoid disease (ES) remains unknown. The objectives of this study were to analyse a large sample of the Franches-Montagnes (FM) horse population and investigate the heritability and mode of inheritance for susceptibility to ES. Horses were clinically examined for the presence of sarcoid tumours. A standardized examination protocol and client questionnaire were used and a pedigree- and subsequent segregation-analysis for the ES trait performed. To investigate the mode of inheritance, five models were evaluated and compared in a hierarchical way.The analyses reveal that variation in susceptibility to ES is best explained by a model incorporating polygenic variation. The possible effect of a major gene, such as specific equine leukocyte antigen alleles, is unlikely, but cannot be ruled-out entirely. The heritability of the phenotype on the observation scale for the trait ‘affected with ES’ was estimated to be 8%. A corrected value for the heritability on a liability scale was estimated at 21% and it is therefore possible to estimate breeding values for ES. The arguments against the practical implementation of an estimated breeding value in a multifactorial condition like ES are discussed.     

Genetic analysis of competition data on Icelandic horses

In a study of the possibility of using competition data in the genetic evaluation of Icelandic horses, data from competitions held in Iceland between 1999 and 2004 and in Sweden between 1998 and 2004 were analyzed to estimate the genetic parameters of competition performance traits. The data-sets from both countries included 18 982 records of 3790 horses in 379 different events. Two types of competition were included: sport competitions and gæðinga competitions performed on oval tracks and on a straight track. Each type of competition involves several disciplines in which the horses are ridden in the various gaits. The traits analyzed were two different measures of four-gait, five-gait and tölt, and one pace trait. In both the four-gait and five-gait tests the gaits walk, trot, tölt and gallop are exhibited. In the five-gait test, pace is also exhibited. The traits tölt and pace are performances of these single gaits. Highly correlated and similar traits were combined, and three new traits relating to tölt, four-gait and five-gait were formed. No large differences in means or standard deviations of traits were found between countries. All traits were approximately normally distributed. Genetic parameters were estimated using linear animal models including the fixed effects of sex, age and event for all traits, and the level of discipline was included for some traits. Random permanent environmental effects were also included. Estimated heritabilities were moderate to high, ranging from 0.18 to 0.21 for sport-competition traits, from 0.33 to 0.35 for gæðinga-competition traits and from 0.19 to 0.22 for combined traits. Estimated genetic correlations between different sport-competition traits varied from 0.63 to 0.96, and between the two gæðinga-competition traits it was estimated at 0.43. Genetic correlations between sport- and gæðinga-competition traits ranged from − 0.42 to 1.00. It was concluded that competition traits are suitable to include in genetic evaluations.     

Variance component estimations for race performance of thoroughbred horses in Brazil by random regression model

A total of 306,698 racing performance data recorded between 1992 and 2002 from 25495 Brazilian Thoroughbred horses was analyzed to estimate the variance components using the Random Regression Model (RRM) compared to the Classical Repeatability Animal Model (CRAM). The performance was evaluated using the race time (in seconds) to run distances of 1000, 1100, 1200, 1300, 1400, 1500 or 1600 meters. The pedigree of each horse was extended as far as possible, with a total of 36,659 animals. The simple correlation between Breeding Value (BV) for the race time estimated by both procedures was high (r = 0.963) when the data were expressed at the mean level of all distances. However, with the RRM it was possible to estimate the genetic parameters and the BV of all animals at the trajectory of each one of the seven distances. Also, results clearly showed that a single BV estimated by CRAM, is neither an adequate nor a sufficient indicator for the selection of the best horses throughout the trajectory of distance performance. We concluded that the RRM procedure is highly recommended for the evaluation of racehorse performance.     

Genetic analysis of racing performance in Irish greyhounds

The aim of this study was to analyse racing performance data in Irish greyhounds with regard to genetic and environmental variation. Estimation of heritabilities for racing time (RT) and ranking, and the prediction of breeding values for all greyhounds in the investigated data were carried out. Data from 42,785 races in Ireland in the years 2000-2003 were available. These results were obtained from 42,880 greyhounds on 20 race tracks over a distance of 480 m. Three traits were analysed, RT, ranking and a scaled logarithmic function for RT (ART), which was used to adjust racing time to be normally distributed. The data were analysed with a bivariate animal model. The estimated heritabilities were moderate for RT (0.31) and ART (0.38), but very low for ranking (0.10). The repeatabilities were 0.56 (RT), 0.51 (ART) and 0.13 (ranking). The genetic correlations were very high, 0.99 (RT-ranking) and 0.96 (ART-ranking), while the phenotypic correlation was lower, 0.60 (RT-ranking) and 0.62 (ART-ranking). The genetic trend for the traits as well as the phenotypic change of the average RT was positive.     

The influence of bedding on the time horses spend recumbent

To determine if bedding has any influence on the time horses spend recumbent, 8 horses kept on straw and 8 kept on wood shavings were observed from 10:00 to 5:30 for two successive nights. Observations were conducted using time-lapse video recordings. Lying down and rising behavior, as well as frequency and duration of bouts spent in lateral and sternal recumbency, was registered. The results showed that horses on straw were lying in lateral recumbency three times longer than horses on shavings (P < .001), whereas the time horses spent in sternal recumbency did not differ. The longest period of noninterrupted lateral recumbency was longer for horses on straw than for those on shavings. Because horses must lie down, preferably in lateral recumbency, to achieve paradoxical sleep, the reduced time spent in lateral recumbency in horses on wood shavings may affect their welfare and performance. Independent of the bedding, we further observed that, as the horses got up from recumbency, most of them made attempts to roll over before rising. This behavior appeared to be caused by some difficulty in rising, possibly due to the box size, and might have a connection with the fact that horses sometimes get stuck against the box wall.

Introduction

Many riding horses spend the majority of their life in an artificial environment. Horse owners keep their horses under certain conditions because of tradition, because they want to make the horse feel comfortable from a human point of view, or to reduce the amount of work involved in horse husbandry. Often the choice of bedding substrate is made from a subjective point of view without assessing both short-term and long-term effects of the bedding. Part of the reason is that only few studies have analyzed horses' preferences for different bedding substrates and their effect on the time horses spend recumbent. In one study comparing straw and wood shavings, no significant preference was found.[1] In another study comparing plastic, wheat straw, and wood shavings, the time horses spent standing, sleeping, or lying down was not affected significantly by the bedding substrates. [2] Mills et al [3] found that horses, given a choice between straw and wood shavings, spent significantly more time on straw. Whereas the substrates had no significant effect on behaviors such as eating, lying, and standing alert, horses spent more time performing bedding-directed behaviors on straw but more time dozing on shavings. Finally, it has been reported that the use of nonstraw bedding may increase the risk of abnormal behaviors such as weaving. [4]As far as bedding properties are concerned, Airaksinen et al[5] concluded that air quality in the stable and utilization of manure can be improved by selecting a good bedding material. According to Reed and Redhead, [6] both straw and shavings are economical and easy to obtain, and they make a bright, comfortable bed. Straw bales are convenient to store, but may be eaten by the horse, are labor intensive, and may be dusty or contain fungal spores. Wood shavings are not eaten by the horse and are good for respiratory problems but need to be kept very clean because they are porous. In addition, they are not as warm as straw because they do not trap air the way straw does.Electroencephalographic (EEG) studies in cats have demonstrated that sleep can be divided into two stages of differing electrocorticographic (EcoG) patterns, ie, slow-wave-sleep (SWS) and paradoxical sleep (PS).[7] During PS, bursts of rapid eye movements (REM) can be seen at irregular intervals. [8] In humans, dreaming occurs during this stage. [9 and 10] Horses are able to sleep while standing, [11] but in this position they only go into SWS. [14, 15 and 16] During PS there is a complete abolition of muscular tone of antigravity muscles and of neck muscles, as shown in cats. [17] In horses, there is a gradual loss of muscular tone until the middle of the recorded SWS period, whence it decreases to a negligible amount during PS. [15] Consequently, muscular tone disappears entirely at the onset of PS. [18] Horses are unable to complete a sleeping cycle without lying down to enter PS. [8, 19 and 20] They normally fall asleep while standing and, when they feel confident about their environment, lie down in sternocostal recumbency. [8] Thereafter, they proceed to lateral recumbency and enter PS. [14 and 19] Dallaire and Ruckebusch [18] demonstrated that the SWS state was infrequent in the standing animal and most often occurred during sternocostal recumbency with the head resting or not on the ground. PS occurred in both sternocostal and lateral recumbency, although the animal frequently had to readjust its position into sternocostal recumbency due to the disappearance of neck muscular tone.The sleep pattern of horses depends on many circumstances, such as age,[21, 22 and 23] diet, [16] and familiarity with the environment. When horses are put outdoors it may take some days before they lie down. If one horse that is familiar with the environment lies down, the others usually follow. [8 and 13] Dallaire and Ruckebusch [16] subjected three horses to a four-day period of perceptual (visual and auditive) deprivation. After this period total sleep time increased due to an augmentation of both SWS and PS. Finally, there is large individual variation between horses in the time they spend recumbent and sleeping. [15]Horses spend 11% to 20% of the total time in recumbency.[11 and 15] Lateral recumbency represents about 20% of total recumbency time, and uninterrupted periods of lateral recumbency vary from 1 to 13 minutes (mean, 4.6 min). [14 and 16] Steinhart [11] found that the mean length of uninterrupted lateral recumbency periods was 23 minutes, the longest period being one hour. Total sleeping time in the stabled horse averages 3 to 5 hours per day or 15% of the total time. [8, 13 and 16] Keiper and Keenan [24] found similar time budgets in feral horses that were recumbent approximately 26% of the night. PS is about 17% to 25% of total sleeping time, and the mean length of a single PS period is 4 to 4.8 minutes. [13 and 18]In stabled horses sleep is mainly nocturnal and occurs during three to seven periods during the night.[8, 13 and 16] Ruckebusch [13] observed that neither sleep nor recumbency occurred during daytime in three ponies observed for a month and, in another experiment conducted on horses, PS occurred only during nighttime. [15] A group of ponies observed for more than a month between 8:45 and 4:45 spent only 1% of the daytime recumbent.[25] The maximum concentration of sleep occurs from 12:00 to 4:00 .[8, 16, 18 and 24]The purpose of this study was to examine two groups of horses in a familiar environment, one group kept on a bedding consisting of straw, and the other kept on wood shavings, and to determine if there was any difference between the two groups in the time they spend recumbent.

Materials and methods

Housing. The study was conducted in one of the biggest riding clubs in Denmark, housing about 150 horses. The 18 horses used in the study stood in three different parts of the stable. They were all stabled in boxes measuring 3 × 3 m and subjected to the same feeding and management routine. They were unable to see their next-door neighbor because of a tall wooden board, but they were able to see the horses stabled on the opposite side of the corridor through bars. Nine horses were stabled on wheat straw (15 cm long, dry matter content 87-88%) and nine on oven-dried wood shavings (80% spruce and 20% pine, dry matter content 82%).Animals. All horses used in the study were privately owned. They had been kept in the boxes in which they were observed a minimum of three weeks. Three of the horses were mares and 15 were geldings. Most of them were Danish Warmblood used for dressage riding. Their ages ranged from 5 to 18 years (mean, 10.6 y) and their height ranged from 1.60 to 1.76 m (mean, 1.68 m). All horses wore a blanket. Age and sex distribution between the two groups is shown in Table 1.     

Variation of gene frequencies in ASIP, MC1R and GREY loci in Thoroughbred horses

The objective of the study has been to verify the hypothesis that the coat colour is regarded in the selection of Polish Thoroughbred horse population. Formally, the colour is not a selection criterion in this breed selected mainly for speed. The material consisted of twelve groups of foals registered in successive volumes of the Stud Book (11,688 foals, in total) and their parents selected to the breeding stud. The frequency of alleles in ASIP, MC1R and GREY loci controlling the coat colours was estimated from the recessive phenotype frequency square in the groups of foals. The inflow of foreign genes was limited and the population great, hence the migration effect was very low. The drift and Wahlund effect hardly influenced the genetic structure in the groups which enabled to analyze the population not divided. The total offspring frequency of recessive a, e and g alleles amounted to 0.1552, 0.4877 and 0.9773, respectively. Accuracy of the assessment of the a and e frequency was confirmed on the basis of test matings. The a, e and g alleles were more frequent in dams than in sires and the a alleles occurred more often in fillies than in colts. The frequency of a and e alleles was higher in the offspring than in the parents. The genotype distribution in the offspring differed from the expected one, assessed from the gamete frequency in sires and in dams. Fewer bay foals were born than anticipated. All the results show that the coat colour is not entirely disregarded in the breeding of Thoroughbred horses. The dominant A and E alleles producing the colour are preferred in the selection, particularly in the sires. This leads to some alterations in the phenotypic structure of the population. On the other hand, the horses are mated randomly, irrespective of the coat colour.     

Impacts of feral horses grazing on rangelands: An overview

The potential impacts on vegetation and watersheds in the western U.S. by feral horses are discussed. Feral horses select open habitats with relatively large amounts of grass. Horse dietsare largely grasses but shrubs are used in some areas. Utilization levels are proportional to animal numbers but equivalent numbers of horses may consume more than cattle because of differing digestive physiology. Predicted vegetation changes under heavy feral horses use may result in range dominated by unpalatable shrubs. Watershed conditions would probably not change except underheavy use by horses when soil compaction, soil disturbance and fouling of water holes could result.     

Development of a composite orthopaedic pain scale in horses

This study addresses development and validation of a composite multifactorial pain scale (CPS) in an experimental equine model of acute orthopaedic pain. Eighteen horses were allocated to control (sedation with/without epidural analgesia - mixture of morphine, ropivacaine, detomidine and ketamine) and experimental groups: amphotericin-B injection in the tarsocrural joint induced pain and analgesia was either i.v. phenylbutazone administered post-induction of synovitis, or pre-emptive epidural mixture, or a pre-emptive combination of the 2. Inter- and intra-observer reproducibility was good (0.8相似文献   

The analysis of densitometric and geometric parameters of bilateral proximal phalanges in horses with the use of peripheral quantitative computed tompgraphy

Background

Proximal phalanges in horses are among bones that are most prone to injuries. So far, the detailed analysis of densitometric and geometric parameters of both front legs proximal phalanges in horses has not been investigated. The aim of this study was to compare the densitometric and geometric parameters between proximal phalanges in equine both front legs with the use of peripheral quantitative computed tomography (pQCT).

Methods

The study material comprised isolated both front legs proximal phalanges derived from 22 horses. The structure analysis of the proximal phalanges was conducted with the pQCT. The following bone parameters were determined: bone mineral content, volumetric bone mineral density, total bone area, trabecular area, cortical area, cortical thickness, periosteal circumference, endocortical circumference, Strength Strain Index. Tomographic analysis of proximal phalanges was conducted at three levels: at 15%, 50% and 85% of the bone length.

Results

The statistical analysis showed that both the densitometric and geometric parameters of the bone at 50% and 85% of its length, did not present any statistically significant differences for the left or right proximal phalanges of the forelimb. At the same time, all examined parameters measured at 15% of the bone length, in the vicinity of the proximal metaphysis revealed significant statistical differences between both front legs proximal phalanges.

Conclusions

The proximal phalanx parameters in the forelimbs are significantly different for the left and right proximal phalanx at 15% of the length and they indicate higher Strength Strain Index of the left bone in this location. The densitometric and geometric parameters of the bone at 50% and 85% of its length, did not present any statistically significant differences for the left or right proximal phalanges of the left and right forelimbs. The most serious changes caused by asymmetrical load of the thoracic limbs in horses occur near the proximal metaphysis, where the spongious substance is most abundant. This may happen because the metabolism of the spongious bone tissue is eight times faster compared to the compact bone tissue. Thus, any changes, including those caused by asymmetrical strain exerted on the right and left thoracic limbs, are the earliest to be observed.     

Genetic parameters of performance traits in horse endurance races

The objective of the study was to find a heritable trait measuring ability in endurance races from competition results in order to select endurance horses from them. The results of 90–160 km endurance races in France from 2002 to 2004 were available including 2795 horses, 3.2 races per horse, from which 2264 had a speed measured, i.e. 5252 measurements of speed and 9059 of placing (0 or 1 when the horse completed the race). The model included fixed effects of sex, age, month of birth (not significant), region of birth, breed, and random effects of permanent environmental effects and animal effect (20,854 horses). Heritabilities were 0.28 and 0.06 (0.10 on underlying scale) respectively for speed and placing. Repeatabilities were respectively 0.44 and 0.07 (0.12). The genetic correlation was 0.87. No genetic differences were found between the results in small distance races (90 km) and long distance races (120–160 km). Additional data on young horses in specific races (20–60 km) with controlled speed did not give a precocious criterion (genetic correlation between speed in adult races and maximum level of distance and difficulty in the young horse equal to 0.07) for selection. In conclusion, breeding values should be calculated from speed and placing in races ≥ 90 km. A higher genetic progress is expected than for other equestrian disciplines since heritability is considerably higher for a trait measured in a single event.     

A reaction norm model approach to estimate the genetic effect of temperature on sportive performance of trotter horses

The performance results of Spanish Trotter Horses were merged with the information from the nearest official weather stations, to estimate the effects of temperature (T) on speed during the day of the race. The resulting data set included: 104 125 individual results from 7653 races with 3772 participant horses and driven by 1402 jockeys. After a classical repeatability animal model in which the effects of T were assumed null, a total of five different random regression models (RRM) with the same fixed part were applied in a parsimonious nested process in which the (co)variance components for each random effect were estimated considering homo/heterogeneous responses across the trajectory of T during the race. The results demonstrate that performance is better when T increases from 4°C to 12°C, followed by a comfort zone (12–19°C) and a light but more stressful zone (>20°C). A significant change in the T during 20 years (+4°C) was observed whilst the speed of the race improved by +2.1 m/s during the same period. The information criterion (LogL, AIC and BIC) confirmed the existence of heterogeneity of (co)variance components along the trajectory of T scale. The model in which T effect was assumed non‐constant across the T scale for animal genetic effects; the individual environmental permanent effects and the jockey effects fit the data better. Heritability had higher values (0.19–0.20) when T was <12°C and slightly decreases within the comfort and stressful zones. Genetic correlations were high and, as was expected, it decreases when difference between T increases. The best 150 animals for speed during the comfort zone were selected according to the Expected Breeding Value (EBV) estimated with the best RRM, and important variations were detected in the evolution of EBV across the trajectory of T. The presence of a genetic base related to T effect during the race in this type of performance is demonstrated.