Pacemaker July, 2003
A question of speed and stamina
Dr. Steve Harrison of The Thoroughbred Genetics Company explains why better results will be obtained by building on known aptitudes rather than trying to modify them with totally dissimilar genes.
What would you get if you crossed Gary Lough with
Paula Radcliffe? No, there is no punch line. It is a serious question. The
world’s greatest human female stayer and her ‘middle-distance’ running
husband who ran 3.34 over 1500m in his prime. A better example might have been
provided if Gary Lough had been a sprinter but there is still quite a
difference between running 1500 metres and over 40,000. Thoroughbred breeders
might learn much from considering the theoretical breeding dynamics of the
A useful model is provided here which humans might
more readily relate to and empathize with. It is also an area where commercial
and selection variables don’t have a role. Moreover, there has been a
considerable amount of money and effort spent on the examination of the role
of physiology and genetics in human athletic performance.
It is a complicated situation but there is already
sufficient evidence in human studies to suggest that some genes, or versions
of genes, implicated in athletic endurance success differ from those with a
greater influence on prowess in power-orientated activities.
There are also numerous
metabolic processes and biochemical cycles going on at any one time in the
cells of an individual. Many of these have a bearing on an athlete’s
ultimate athletic niche, for instance those involved in energy release in the
muscles. It is clear that certain metabolic cycles can be categorised as to
whether their influence is more pronounced with regard to power or endurance
events. For instance some biochemical processes have a role in breaking down
specific high energy compounds during a marathon but not in a 100 metres
sprint. There can be at least 30 genes controlling some of the cycles.
Within these biochemical
cycles some gene versions are more efficient in doing their jobs than others.
Therefore, an individual’s athletic career route can be determined, at least
in part, by the relative efficiencies and strengths of gene versions involved
in the different biochemical cycles which primarily favour either endurance or
This logically suggests
that an aspiring prodigy born to athletic parents has a more predictable
athletic future if his or her parents competed successfully in similar events.
This would provide greater consistency by reproducing genetic strengths
contributing to the same athletic goal rather than providing genetic
improvement in ‘non-targeted’ and physiologically ‘incompatible’
There is not enough
evidence to show that a 1500m runner has wildly different genetic requirements
to a marathon runner but this example might be more appropriate in translating
these observations into an equine format where race distance variability is
less clear cut.
There is no such major
variance in the distances of races run by Thoroughbreds where a marathon is
400 times the distance of a 100m sprint. He we are looking at a situation
where the difference may only be two or three fold between all major race
distances. Given this situation, the physiological and genetic differences
between ‘sprinting’ and ‘staying’ Thoroughbreds may be subtler.
However, it is clear
from the fact that sprinters cannot perform well over longer distances and
that the form of various horses does take a dip when tried over extended
distances that different mechanisms are at work in determining a horse’s
For instance, there are
certainly differences in distribution of muscle fibre types between stayers
and sprinters. Crossing animals from the two groups does seem to result in
animals with intermediate fibre distribution but, as with humans, there are
many other genetic variables that will play a role in determining the final
If the human model
suggests that there is athletic specialization of specific body types between
a 100m runner and a 400m runner, which is more in the ‘ball park’ figure
of the range of horse racing distances, then it is probably true that this
also applies to horses.
Distance categories are
less well defined in horse racing and there is a main genetic grey area in the
‘pay dirt zone’ between a mile and ten furlongs. The uncertainty as to whether a top-class horse is capable of
‘getting’ the longer distance is curious given the fact that changes in
training regime might be capable of swinging a horse’s performance by one or
two furlongs extra. However, this would suggest that it is difficult to place
horses into convenient tidy little distance packages within this group and
that genetic potential is highly horse specific. Many of the horses running
over the variety of middle distance races and sprints look similar and differ
probably in their physiology rather than conformation.
Whilst the racing industry has its different tiers
of operation, it is now perennially argued that racing attention has become
generally focussed commercially on the shorter to shorter middle distance
races. Generally, breeders seem to be attracted towards producing horses that
fall into the 8-10f category.
They are more valuable and it is understandable
that breeders will try to breed horses which are more specialised and not
compel trainers to waste time on producing an ‘all-rounder’.
The Ascot Gold Cup and The St. Leger were once
popular races and horses could be unashamedly bred with the possibility of
winning these races as an objective. For a variety of reasons, this has
changed. It is possible that the influx and influences of American bloodstock
and racing objectives have played a major role. Horses, which could compete over a wide range of distances,
are very rare and a winner of an English ‘triple-crown’ is an unlikely
It is true that some winners of the Derby could
perform well in The St. Leger and others may not be disgraced in the Two
Thousand Guineas but the potential to exceed in all is diminished. Regardless
of whether this is due to increased competition, lack of interest, commercial
pressures or greater specialisation within given distances, it would now
appear that more horses tend to fall into a narrower range of stamina
categories than previously seen.
The true longer distance horse was
conformationally different from the speedier horse. It could be argued that
this is now less true, as horses bred to run over longer distances on the flat
no longer exist and those that do are discarded failures from races over the
shorter distances. To be bred for
extended stamina is now an accident and colts with the ability to perform over
longer distances hold no attraction in the breeding world.
Does this mean that
there is less genetic difference between Thoroughbreds in general? The answer
is ‘probably not’. There has just been a shift of emphasis and a change in
dynamics. The increased popularity of two-year-old racing has undoubtedly led
to an increase in the number and subsequent popularity of sprint and miler
stallions. We have a situation where stamina-orientated stallions are
sidelined as un-commercial. But there is still a mish-mash of genetic
diversity as stamina attributes are maintained through mares and damsires.
These factors mean that there is probably more chance than ever of being
tempted to cross animals that are dissimilar with each other.
This means that we still
have a Thoroughbred population carrying a mixture of genes with some affecting
stamina potential more that sprinting potential and vice versa. There
is ample genetic material to suggest that what we can learn from human systems
is applicable to horses. If stamina and sprinting attributes are controlled by
genetic mechanisms or genes that are diametrically opposed then attempting to
compensate for a deficiency in speed or stamina by crossing a mare with a
stallion of the opposite extreme might not be the best ploy.
Similarly, the common
policy of stallions of low stamina index with mares of opposite extremes in
order to produce a middle distance runner may work in some cases but it is
genetically more likely to produce neither one thing not the other and
statistically more likely to end in failure.
The economics of
breeding and racing puts the emphasis on the quick fix but it may not be
possible to achieve a breeding objective in the space of one generation by
crossing dissimilar animals together. In ‘fixing’ other multi-genetically
controlled characteristics in other species it is often necessary to
back-cross animals over a number of generations to animals with the desired
characteristics. Alternatively, line-breeding using animals with the desired
traits may work.
Most breeders don’t
have the time to do this. Also many people take pot-luck on the outcome of a
mating. There are different distances of race, ground conditions, track etc
and a horse may find its niche eventually.
It can be argued that,
to get the best from a mare, irrespective of her stamina range, it is better
to accept her limitations and reinforce her primary qualities by crossing her
with a stallion of similar stamina influence. There are obviously more
pedigree and genetic parameters in play but this increases the chances of
‘concentrating’ genes compatible for doing the same job rather than
creating a mixed bag of genes that cancel each other out. The theory also
holds true for the reverse in the case of the stallion. This does not
necessarily lead to an increase in inbreeding. Crossing unrelated horses with
similar stamina attributes may not only concentrate compatible genes but also
enhance hybrid vigour.
Breeding compatible genetic components into the one horse is important and should possibly be borne in mind as a target. Putting a Formula 1 engine into a tractor is not necessarily going to make an efficient touring car.
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