Risk factors for being an unsuccessful two-year old
race horse
Student:
Studentnr.:
Address:
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Sanne Willemien Steenhuisen
0249084
Hoogdorperweg 17D
1965NB Heemskerk
The Netherlands
0031(0)6-27530273
the_only_sanne@hotmail.com
Location of project:
Local supervisor:
Supervisor at UU:
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Duration:
Massey University, Palmerston North, New Zealand
Dr. C.W. Rogers
Prof. P.R. van Weeren
17-7-2008
12 weeks
Abstract
Background
The primary reason for the loss of horses from training and racing is musculoskeletal
injury, especially dorsal metacarpal disease. Research has shown that the occurrence
of injuries is related to the intensity of the exercise programme. Short periods of high
speed exercise in the training seem to be beneficial, as especially bones can adapt to
the high speed, so horses are better prepared for racing speeds.
Aims
To describe the differences between horses who go straight through training as a twoyear-old and horse who have interruptions in their training.
Methods
The data, containing 597 two-year-horses, were obtained by Perkins over a 34-months
period from October 1997 until July 2000. For every horse the training activity score
(TAS) was recorded, as well as the amount of days it had spent in that TAS. Different
TAS were: TAS 1= spell, TAS 2= walk/trot, TAS 3= canter, TAS 4= gallop/high
speed exercise, TAS 5= starting in a race or trial. Also recorded were the reasons why
horses were put on a spell; voluntary or injury related.
Results
The two-year-olds were divided in three different groups: “Good” horses (n=279, no
spells), “Voluntary” horses (n=144, just voluntary spells) and “Involuntary” horses
(n=132, at least one injury-related spell). There was a significant difference between
the good group and the voluntary/involuntary group in TAS already at the start. The
voluntary and involuntary groups both had a big dip in TAS at the beginning of
training, but after that the voluntary group went significantly faster to reach TAS 5
than the involuntary group (p<0.05). Of the voluntary group 50% of the horses
reached TAS 5. Of the involuntary horses only 30% reached TAS 5.
Of all the horses that reached TAS 5, the good horses (median=114 days) were
significantly faster (p<0.01) to reach TAS 5 than the voluntary/involuntary horses.
There was no difference between the voluntary (median=244 days) and involuntary
groups (median=244 days).
Voluntary horses were faster to reach their first spell than involuntary horses (p<0.01).
Both groups had their first spell early in the training. Involuntary horses had more
than one spell more often than voluntary horses.
In the good group, older two-year-olds were faster to reach TAS 5 than the youngest
(p<0.01) and middle (p=0.028) groups of two-year-olds. In the voluntary group, the
middle group of two-year olds were faster to reach TAS 5 than the early two-yearolds (p=0.014).
Horses that were born in the year 1995 were faster to reach TAS 5 than horses born in
the year 1996 (p=0.013) and the year 1997 (p=0.003).
2
Conclusions
The critical point of horses ending up in a group is early on in the training. Trainers
may have a good view on whether a horse is going to be a good one and they will
train such a horse quickly up to TAS 5. Voluntary horses might be the horses that are
obviously not ready to cope with the training and are put on a spell by their trainer.
Involuntary horses could be the horses that the trainers were in doubt about whether to
put them on a spell or not, then were trained further and subsequently sustained an
injury. When in doubt it would therefore be wise to put the horse on a voluntary spell,
as horses in this group have a much higher chance of reaching TAS 5 and a lower
chance of being put on another spell, than horses in the involuntary group.
Late two-year-olds have an advantage on younger two-year-olds. This could be due to
these horses being stronger and more developed or having received more pre-training.
There is an effect in the year of birth the horses were born in. This shows that factors
such as weather and track conditions have their influence.
3
Table of contents
INTRODUCTION ..................................................................................................................................... 5
Wastage in general ......................................................................................................................... 5
DMD ............................................................................................................................................... 5
Fractures ......................................................................................................................................... 5
CMSI ............................................................................................................................................... 6
Tendon / soft tissue.......................................................................................................................... 6
MSI general..................................................................................................................................... 6
Hypothesis: ..................................................................................................................................... 6
MATERIALS AND METHODS .................................................................................................................. 7
Statistical analysis .......................................................................................................................... 7
RESULTS ............................................................................................................................................... 8
Parameters ...................................................................................................................................... 8
Differences between Good, Voluntary and Involuntary groups ...................................................... 8
Successful/unsuccessful horses ..................................................................................................... 10
Timing of spells ............................................................................................................................. 11
Difference in age ........................................................................................................................... 12
Difference in years of birth ........................................................................................................... 14
Differences between districts ........................................................................................................ 15
DISCUSSION ........................................................................................................................................ 15
Two groups ................................................................................................................................... 15
Good vs. bad horses ...................................................................................................................... 15
Voluntary horses ........................................................................................................................... 16
Involuntary horses ........................................................................................................................ 16
Comparing involuntary and voluntary horses .............................................................................. 16
Risk factors ................................................................................................................................... 17
REFERENCES....................................................................................................................................... 18
4
Introduction
Wastage in general
The primary reason for the loss of horses from training and racing, often termed
wastage, is musculoskeletal injury (Bailey et al. 1997; Jeffcott et al. 1982) However,
the relationship between training exposure and risk is not straightforward. The risk
and nature of the musculoskeletal injury changes as a training programme progresses
and with increasing age (Perkins et al. 2005b). It is therefore important to examine the
reasons for wastage either according to injury type, or by age and class of the horse.
In the interest of clarity, risk of injury will be presented according to injury category
within this review.
DMD
Dorsal metacarpal disease is the single largest reason for wastage in young (2-yearold racehorses). Estimates of the percentage of horses affected differs between racing
regions with estimates ranging from 20 – 70% of all 2 year olds in work (Bailey et al.
1998; Norwood 1978; Perkins et al. 2005a). A possible reason for the variation
between populations could be due to differences in early preparation, surfaces worked
on and the structure of the racing or training programme.
Research has shown that cortical and especially cancellous bone responds rapidly to
training exercise (Firth and Rogers 2005). Training for prolonged intervals at slower
speeds will induce a modelling response, which is inappropriate for racing speeds
(Nunamaker et al. 1990). Nunamaker actually designed a training schedule aimed at
reducing the incidence of fatigue damage to the third metacarpal bone by cutting the
extent of the low speed work and increasing the frequency of short interval high speed
work. This stimulates an appropriate modelling response, with minimal risk of fatigue
damage.(Boston and Nunamaker 2000).
Verheyen found that the risk of dorsal metacarpal disease (DMD) decreases with
accumulation of distances at canter and gallop. However, accumulation of exercise
distances in short periods increases the risk of dorsal metacarpal disease (Verheyen et
al. 2005).
The incidence of DMD in two-year-old race horses is high. However, the incidence in
three-year-olds is a lot lower (Bailey et al. 1998), which could also be due to the
modelling response of the bone, as three year-olds have had a year more training
exposure, so the bone has had time to adapt to the exercise.
Fractures
Research has shown that in previously untrained bones, there was an increased risk of
fracture with an accumulation in canter exercise. Accumulation of high-speed gallop
exercise seemed to have a protective effect, as the risk of fractures decreased with
more exercise at the gallop. Horses doing no gallop work at all during training were at
an increased risk of fracture on the racecourse (Parkin et al. 2004) However, when
accumulation of canter and gallop exercise increases in a short time period, the risk of
fractures is increased (Verheyen et al. 2006).
A large proportion of fractures occur in the absence of a specific event and show
typical signs of stress fractures. They are often associated with pre-existing pathology
and frequently share the same locations as incomplete cracks. Intense training before
the adaptive response is completed increases the risk of fatigue damage. Fatigue
damage is associated with progressive micro damage. However, the biological repair
5
mechanism of bone (remodelling) is also important. Horses exercised before bone
repair is complete are likely to be at greater risk for catastrophic stress fracture (Riggs
2002).
CMSI
Studies reported that the total distance accumulated during a two-month period was
positively associated with the risk of catastrophic musculoskeletal injury (Estberg et
al. 1996). It was also reported that the risk of catastrophic MSI was greatest within 30
days of a period of above average high-intensity exercise (Estberg et al. 1998)
Tendon / soft tissue
Hill found that suspensory apparatus failure was related to a higher intensity of recent
exercise. It was also found that the longer the interval was since the last period of 60
or more days without a race or timed workout, the higher the risk of suspensory
apparatus failure (Hill et al. 2004).
MSI general
Research indicated that increasing cumulative racing distances were associated with
an initial reduction in the odds of MSI, that then levelled out and finally increased
again as the cumulative racing distance was increased further (Perkins et al. 2005b)
Another study showed an association between increasing the average distance at high
speeds and an increased risk of injury. It also showed a correlation between the
amount of fast days within the fast intervals and musculoskeletal injuries (Cogger et
al. 2006).
In this project, we focus on the differences between successful and unsuccessful
horses. We further look at the differences in training between “good” and “bad”
horses and try to identify the risk factors for horses having an unsuccessful two-yearold racing campaign.
It is hypothesised that:


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
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

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The median number of days until the first race (or trial) start will be higher in
‘setback’ horses compared to healthy horses.
Horses in the ‘setback’ group are significantly less likely to start in a race than
healthy horses.
Horses accumulating a higher number of training days at TAS 2 or 3 will be at
an increased risk of having ‘setbacks’.
The risk of further ‘setbacks’ increases as the number of days spelling
increases.
Horses with involuntary “setbacks” are less likely to start in a race than horses
with voluntary “setbacks”.
The number of days until the first start will be higher in involuntary “setback”
horses, than in voluntary “setback” horses.
Late two-year-olds are less likely to be in the “setback” group.
The relative proportion of “setback” horses in each year of birth will be the
same.
The relative proportion of “setback” horses will be the same in different NewZealand districts.
6
Materials and methods
The data were initially obtained during a longitudinal study conducted by Perkins et al.
(2004) over a period of 34 months, starting in October 1997 and ending in July 2000.
The initial dataset was meant for only 2 year old horses and represents data from
twenty different trainers located in either the central and northern North Island region
of New Zealand.
The trainers were a sample of licensed professional Thoroughbred trainers and were
training at 5 different regional training venues. The data contain a total of 597 twoyear old Thoroughbred race horses.
Daily records of the training and injury status of the horse were collected. At the end
of each data collection period (usually 2 – 3 weeks) a summarising training activity
score was allocated to best describe the training level of the horse during the
observation period. The Training activity scores (TAS) were allocated using the
following criteria,
TAS = 1: Spell
TAS = 2: Walk or trot
TAS = 3: Activity up to but not exceeding a canter
TAS = 4: Galop/fast work but not yet started in a trial or race
TAS = 5: Horses that have started in at least one trial or race
For analysis the sequence in which the horses were trained at a particular TAS and the
numbers of days spent in that TAS were examined. One sequence equals the time the
horse spent in one particular TAS. The number of sequences a horse went through
depends on the number of times it received a set back, i.e. it was put back on a lower
TAS. A spell was recorded if the horse was put on a spell for more than 7 days.
The reasons for putting a horse on a spell were recorded as being voluntary,
immaturity or injury related (involuntary). Injuries were classified according to the
body system involved; musculoskeletal, respiratory, etc and are described in detail in
Perkins et al (2004). Specific information about anatomic location and diagnosis by a
veterinarian were also collected.
Statistical analysis
The statistical analysis and data processing were performed using SPSS version 16.0
(SPSS Inc, Chicago, Il, USA).
To examine the relative representation of the horses in the different age, year of birth
and region categories Chi-square tests were used.
To examine the effect of variables on the time until event (TAS5 or first spell)
Kaplan-Meier survival analysis was used with a log rank test to compare between
groups. To examine the differences in the relative ranking of variables the KruskalWallis test was used. For all analysis the significance level was set to p<0.05.
7
Results
Parameters
Within the dataset there were 597 two-year-old horses, divided almost equally into
groups of male and female. The horses were trained by twenty different trainers, who
were training at five different tracks. The central districts region consisted of the
Awapuni, Foxton and Levin training centres / tracks and the Northern region
consisted of the Cambridge and Matamata training centres. The horses were not
equally divided between districts. More horses were trained in the northern district
(table xyz). The horses in the dataset were born in 1995, 1996, 1997 or 1998. The
majority of the horses in this dataset were born in 1996 and 1997.
Table 1: Parameters of the dataset
Parameter
Sex
Female
Male
District
Central
North
Year of birth
1995
1996
1997
1998
Group
“Good”
“Involuntary”
“Voluntary”
Number of horses
282
315
259
338
58
241
265
33
279
132
144
Differences between Good, Voluntary and Involuntary groups
Within the dataset there were 279 horses that had an uninterrupted training schedule
from entry into the stable until they reached TAS 5 (having a trial or race start). These
were identified as “good” (G) horses. On the other side there were horses with at least
one injury-related spell, they were identified as “involuntary” (I) horses. A third group
was identified as “voluntary” (V), as they did have spells, but these were only
voluntary spells (horses on a spell because of immaturity were also put in this
category, because it still was the discission of the trainer to put the horse on a spell).
The horses were not equally distributed between the different categories. Half of the
population belonged to the good horses and the remaining half were equally divided
into involuntary and voluntary horses (p<0.05). From an administrator’s view this
demonstrated that 50% of the horses are successful in reaching TAS 5 without any
spells.
8
6
5
4
TAS
Good
3
Voluntary
Involuntary
2
1
0
0
50
100
150
200
250
300
350
400
450
days
Figure 1: The median TAS and median days spent in that TAS, for three different groups; good
horses, involuntary horses and voluntary horses
Table 2: Parameters of training for three different groups
Sequences
Parameter
1
2
3
4
5
No. of horses
“Good”
279
224
107
20
1
“Voluntary”
144
144
108
85
43
“Involuntary”
132
132
103
82
57
Median TAS
3
5
5
5
5
“Good”
2
1
2
4
4
“Voluntary”
2
1
2
2
3
“Involuntary”
Median cum. days
35
86
146
223
276
“Good”
38
103
126.5
178.5
234.5
“Voluntary”
44
99
135
176
217
“Involuntary”
6
7
8
9
20
38
8
22
6
7
3
2
-
-
-
-
5
2
2.5
3
3.5
4
4
5
-
-
-
-
277
252
307.5
285.5
361.5
327.5
410.5
392
The median TAS of the Good group is in sequence 1 to 4 significantly higher than the
median TAS of the Voluntary group (p<0.01). In the 5th sequence there is no
significant difference.
The median TAS of the Voluntary group has no significant difference with the
Involuntary group in the first sequence. In the second sequence the Involuntary group
has a significantly higher median TAS than the Voluntary group (p=0.004). In
sequence 3 to 6 the Voluntary group has a significantly higher median TAS than the
Involuntary group (p<0.05). In sequence 7 to 9 there were no significant differences,
possibly due to the small number of horses remaining.
9
Figure 2: Kaplan-Meier survival function of good, involuntary and voluntary horses.
Table 3: Median days till TAS 5 for three different groups.
n
Median (95% CI ) days to TAS 5
Good
279
114 (109-119)a1
Involuntary
42
244 (225-263)b
Voluntary
77
244 (233-255)b
For the amount of days it took each group to reach TAS 5, significant differences
were found between the good horses and the voluntary horses (p<0.01) and between
the good horses and the involuntary horses (p<0.01). There was no significant
difference between the groups of voluntary and involuntary horses.
Successful/unsuccessful horses
Within the groups of voluntary and involuntary horses there were a number of horses
that after one or more spells reached TAS 5; they were called successful involuntary
or voluntary horses. Horses that never reached TAS 5 were called failure horses.
“Involuntary”- “failure”= 90 horses
“successful” = 42 horses
“voluntary”- “failure”= 67
“successful”= 77 horses
1
Different superscripts show significant difference (p<0.05)
10
Table 4: Days spent at different TAS for five different groups
Median days spent at TAS
TAS 1
TAS 2/3
TAS 4
Group
Good
0
16
0
Involuntary failure
110,5
57,5
38,5
Involuntary successful 59,5
84
24,5
Voluntary failure
109
32
0
Voluntary successful
85
55
0
TAS 5
66
0
50
0
62
Table 4 shows the total number of days spent at a particular group for all five groups.
In the good group the horses spent a small amount of time in TAS 2 or 3 and went
quickly on to TAS 5. In the involuntary group the failure horses spent almost twice as
much time in TAS 1 than the successful horses did. In the voluntary group the failure
horses spent most of their time in TAS 1. Successful horses did spend a bit of time in
TAS 1 but then went quickly on to TAS 5.
Timing of spells
Figure 3: Kaplan-Meier survival function of days until the first spell for involuntary and
voluntary horses.
11
If a horse had a spell it would have the spell earlier in the training programme if it was
in the voluntary group (p<0.01). In both groups the median number of days until a
spell occurred within the first 2 months of training (for discussion note that this is
before the median race start date for horses in New-Zealand)
Table 5: Days to first spell for two different groups
n
Median (95% CI ) days to first spell
Involuntary
42
67 (60-74)a
Voluntary
77
48 (43-53)b
Table 6: Number of spells in the three groups
No. of spells
Good
Involuntary
0
279
0
1
0
81
More than 1
0
51
Voluntary
0
129
15
It can be seen that the voluntary horses often have just one spell, where the
involuntary horses have more than one spell.
Difference in age
The age when two-year-olds starting training was not equally distributed; the majority
of the horses started training between 20 -25 months (p<0.01).
Figure 4: Kaplan-Meier survival function of 3 age groups within the good horses.
12
In the group of “good” horses, the horses older than 25 months reached TAS 5
significantly earlier than horses within the group of 20-25 months (p=0.028) and
horses within the group younger than 25 months (p<0.01)
Table 7: Good horses divided into age groups
n
Median (95% CI ) days to TAS 5
Younger than 20 months 66
131 (118-144) b
Between 20-25 months
138
114 (104-124)b
Older than 25 months
75
107 (98-116)a
Figure 5: Kaplan-Meier survival function of 3 age groups within the voluntary horses.
In the voluntary group, horses within the group of 20-25 months were significantly
(p=0.014) earlier to reach TAS 5 than the horses younger than 20 months.
Table 8: Voluntary horses divided into age groups
n
Median (95% CI ) days to TAS 5
Younger than 20 months 33
266 (243-289) a
Between 20-25 months
42
236 (219-253)b
Older than 25 months
2
173
In the involuntary group there was no significant difference between the age groups
13
Table 9:Involuntary horses divided into age groups
n
Median (95% CI ) days to TAS 5
Younger than 20 months 14
228 (204-251)
Between 20-25 months
24
245 (227-263)
Older than 25 months
4
210 (121-299)
Difference in years of birth
Figure 6: Kaplan-Meier survival function of three different years of birth.
A significant difference in reaching TAS 5 was found between the horses born in
1995 and 1996 (p=0.013). A significant difference was also found between horses
born in 1995 and 1997 (p=0.003). No significant difference was found between horses
born in 1996 and 1997.
Table 10: Days to TAS 5 for different years of birth
Year of birth
n
Median (95% CI ) days to TAS 5
1995
41
138 (125-151)a
1996
165 138 (119-257)b
1997
192 140 (126-149)b
No horse from the year 1998 had reached TAS 5.
14
Differences between districts
No significant difference in reaching TAS 5 was found between different districts.
Table 11: Days to TAS 5 for different districts
n
Median (95% CI ) days to TAS 5
Central district
142
133 (124-142)a
North district
256
147 (129-165)a
Discussion
Two groups
The results clearly identify two distinct populations of two-year-old racehorses. There
is an obvious successful group among the two-year-old racehorses, which proceeds
straight through to TAS 5 without any spells or injuries. The other group consists of
horses that had spells, either voluntary or involuntary. The good horses make up about
50% of the population, which means half of the horses in training had at least one
spell during their two-year old campaign. If the horses had a spell there is just a 40%
chance of them reaching TAS 5 as a two-year-old.
It’s obvious that everybody wants a good horse. They reach TAS 5 earlier than the
horses in the other groups and therefore provide a better return on investment. Also,
the export / trading market is focused around two-year-olds, so therefore it is
important to have them in a trial or race a soon as possible. From there they can be
sold to, for example, Asia, or raced to try to win back the investment in purchase price
and costs of training.
Good vs. bad horses
Figure one, which shows the median TAS against median days spent in that TAS,
clearly shows the progression in training of the good group. After training for one
sequence, their TAS was already significantly higher than for the horses in the
involuntary or voluntary groups. The good horse had achieved a TAS 5 after a median
of 86 days training. These are the horses a trainer wants, because they are ready to
race or trial after a relatively short training period.
The results show that these horses start out at a higher TAS. This means the trainer
must have a good idea in the beginning of training if the horse is a good horse or not.
Good horses spend little time at a lower TAS and then spend most of their time on a
higher TAS. This means that if a trainer is convinced that the horse falls in this
category, he or she can quickly progress to high speed exercise, instead of spending a
lot of time at lower speeds.
Figure two also shows a clear difference between the good horses and the
involuntary/voluntary group. The median of the good horses versus the other horses
differed by130 days, but the pattern of survival was similar. This shows that the 130
day difference between the groups is due to a delay at the beginning of training of the
voluntary/involuntary groups. These results also show that the delay happens in the
first part of the training.
15
Voluntary horses
In the pattern of the voluntary group it can be seen that they start out at lower TAS.
They then make one dip in TAS, which is probably related to the timing of their spell
period. After this dip they go straight to TAS 5. The median of horses in this group
reached TAS 5 after 277 days. The obvious big dip in TAS in the beginning of the
training of voluntary horses could be related to the fact that voluntary horses are put
on spells because the trainer makes the decision to put them out for a spell.
Apparently most trainers make a quick decision in the beginning of training that some
horses are not yet ready to be trained further, deeming it better to wait with the
training until the horse is ready. Half of the horses that are voluntary actually make it
to TAS 5, so the chance that a horse on a voluntary spell is going to end up racing is
not big.
It can be seen that the successful horses spend time in TAS 1, but otherwise they
have the same pattern of days spent at different TAS as the good horses. Although the
successful voluntary take more time to reach TAS 5 because of their spell at the
beginning, they are still worth putting time in as they will reach TAS 5. Unsuccessful
voluntary horses just spend a lot of time in the lower TAS categories, so if it would be
possible to identify these horses early on, that would be a big benefit for the owner of
the horse.
Involuntary horses
The group of involuntary horses also has the dip in sequence two although they don’t
go down as much as the voluntary group. After that they don’t go straight through to
TAS 5, but keep having dips in their TAS. The median of the horses in this group
does not reach TAS 5 until after 400 days.
In the chart it can be seen that the involuntary horses not only go up slower than the
voluntary after the initial dip, but have more dips in their TAS later on. This is
probably due to the fact that a lot of involuntary horses have more than one spell. One
could question if it is worthwhile to put more money in a horse that had an
involuntary spell, as only a third of the horses actually make it to TAS 5, it takes them
almost 300 days more than the good horses to reach it, and they have a big chance of
re-injury or having a spell again.
In table 4 it can be seen that the successful involuntary horses spent almost two
months less in TAS 1 than the unsuccessful horses. This could mean that the
successful ones have just one spell or spent a lot less time to recover in their first spell.
This means it might not be worthwhile to spend more time and money training a horse
that has been on a spell for more than two months.
Comparing involuntary and voluntary horses
Figure 3 shows the survival curve until the first spell for both the voluntary and
involuntary group. It shows that the median time until the first spell for the voluntary
group is just 48 days. The median time until the first spell for the involuntary group is
67 days, significantly later than the voluntary group. Both survival curves show that
the first spells do indeed occur in the first two months of training. This shows that the
critical point of a horse becoming a good or involuntary/voluntary horse might lie in
the first two months.
That the voluntary horses have their first spell significantly earlier than the
involuntary is probably a result of the different ways horses end up in these groups.
The voluntary group is a result of the choice of a trainer to put the horse on a spell. If
16
the horse was too immature or could obviously not cope with the work it was doing it
would be put on a spell. Therefore, these horses were put on a spell before they had
reached their limit.
Involuntary horses are put on a spell because of an injury and had therefore already
passed their limit.
An explanation for the higher amount of days until the first spell of involuntary horses
might be that the involuntary horses were the horses were it was doubtful whether
they were too immature or could cope with the work. These horses then may have
continued training and subsequently sustained an injury requiring a spell for recovery.
This means that it could be preferable to put a horse on a spell when in doubt, rather
than continuing training it until it possibly breaks down. The advantage of this
approach could be that the horses will have a bigger chance of competing in a race, as
significantly more horses in the voluntary group than the involuntary group eventually
reach TAS 5.
Risk factors
Figure 4 shows the difference between the different ages within the two-year-old
horses. The older horses are significantly faster to reach TAS 5 than the younger
horses. It can also be seen that there are hardly any older horses in the voluntary or
involuntary group, so the older horses (older than 25 months) are not only the fastest
to reach TAS 5, but they also hardly have any spell periods. The reason for this could
be that older horses are stronger and more developed, so they are less likely to get an
injury or to be regarded as not ready for training (thus ending up in the voluntary
group). It could also be that these horses did have a bit of pre-training before and were
therefore already stronger and more adapted to the exercise. This shows that it’s not
advantageous for owners and trainers to try to have a young two-year-old as quickly
as possible ready to race, as they have a bigger risk of injury during training and in the
end take a longer time to eventually start in a race.
As shown by figure 6, a significant difference can be found between different years.
This shows that there are factors each year which influence the success of training of
two-year-old racehorses. Weather and track condition are the most likely factors that
can be supposed to make a difference between the training results in different years.
17
References
Bailey, C.J., Reid, S.W.J., Hodgson, D.R., Bourke, J.M. and Rose, R.J. (1998) Flat,
hurdle and steeple racing: risk factors for musculoskeletal injury. Equine
Veterinary Journal 30, 498-503.
Bailey, C.J., Rose, R.J., Reid, S.W.J. and Hodgson, D.R. (1997) Wastage in the
Australian Thoroughbred racing industry: A survey of Sydney trainers.
Australian Veterinary Journal 75, 64-66.
Boston, R.C. and Nunamaker, D.M. (2000) Gait and speed as exercise components of
risk factors associated with onset of fatigue injury of the third metacarpal bone
in 2-year-old Thoroughbred racehorses. American Journal of Veterinary
Research 61, 602-608.
Cogger, N., Perkins, N., Hodgson, D.R., Reid, S.W.J. and Evans, D.L. (2006) Risk
factors for musculoskeletal injuries in 2-year-old Thoroughbred racehorses.
Preventive Veterinary Medicine 74, 36-43.
Estberg, L., Gardner, I.A., Stover, S.M. and Johnson, B.J. (1998) A case-crossover
study of intensive racing and training schedules and risk of catastrophic
musculoskeletal injury and lay-up in California Thoroughbred racehorses.
Preventive Veterinary Medicine 33, 159-170.
Estberg, L., Stover, S.M., Gardner, I.A., Drake, C.M., Johnson, B. and Ardans, A.
(1996) High-speed exercise history and catastrophic racing fracture in
Thoroughbreds. American Journal of Veterinary Research 57, 1549-1555.
Firth, E.C. and Rogers, C.W. (2005) Musculoskeletal responses of 2-year-old
thoroughbred horses to early training. Conclusions. New Zealand Veterinary
Journal 53, 377-383.
Hill, A.E., Gardner, I.A., Carpenter, T.E. and Stover, S.M. (2004) Effects of injury to
the suspensory apparatus, exercise, and horseshoe characteristics on the risk of
lateral condylar fracture and suspensory apparatus failure in forelimbs of
Thoroughbred racehorses. American Journal of Veterinary Research 65, 15081517.
Jeffcott, L.B., Rossdale, P.D., Freestone, J., Frank, C.J. and Towersclark, P.F. (1982)
An Assessment of Wastage in Thoroughbred Racing from Conception to 4
Years of Age. Equine Veterinary Journal 14, 185-198.
Norwood, G.L. (1978) Bucked-Shin Complex in Thoroughbreds. Proceedings of the
Annual Convention of the American Association of Equine Practitioners 24,
319-336.
Nunamaker, D.M., Butterweck, D.M. and Provost, M.T. (1990) Fatigue Fractures in
Thoroughbred Racehorses - Relationships with Age, Peak Bone Strain, and
Training. Journal of Orthopaedic Research 8, 604-611.
18
Parkin, T.D.H., Clegg, R.D., French, N.P., Proudman, C.J., Riggs, C.M., Singer, E.R.,
Webbon, P.M. and Morgan, K.L. (2004) Horse-level risk factors for fatal
distal limb fracture in racing Thoroughbreds in the UK. Equine Veterinary
Journal 36, 513-519.
Perkins, N.R., Reid, S.W.J. and Morris, R.S. (2005a) Profiling the New Zealand
Thoroughbred racing industry. 2. Conditions interfering with training and
racing. New Zealand Veterinary Journal 53, 69-76.
Perkins, N.R., Reid, S.W.J. and Morris, R.S. (2005b) Risk factors for musculoskeletal
injuries of the lower limbs in Thoroughbred racehorses in New Zealand. New
Zealand Veterinary Journal 53, 171-183.
Riggs, C.M. (2002) Fractures - A preventable hazard of racing thoroughbreds?
Veterinary Journal 163, 19-29.
Verheyen, K., Price, J., Lanyon, L. and Wood, J. (2006) Exercise distance and speed
affect the risk of fracture in racehorses. Bone 39, 1322-1330.
Verheyen, K.L.P., Henley, W.E., Price, J.S. and Wood, J.L.N. (2005) Training-related
factors associated with dorsometacarpal disease in young Thoroughbred
racehorses in the UK. Equine Veterinary Journal 37, 442-448.
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