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Horse Genetics for Speed
Paul R Earl
Facultad de Ciencias Biológicas
Universidad Autónoma de Nuevo León
San Nicolás, NL 66451, Mexico
Prologue
Horse genetics including systematics and
phylogeny, the genetics of morphologic traits,
color variation and the inherited diseases,
molecular genetics, immunogenetics, genetic
aspects of diseases, cytogenetics and gene
maps, linkage and modern breeding
technologies, behavioral and developmental
genetics, genetic conservation, the genetics of
performance traits, conformation, locomotion
and physiological traits, genetic improvement
and standardized genetic nomenclature for the
horse are all touched on in The Genetics of the
Horse by Ann T. Bowling & A. Ruvinsky, Editors,
CAB Inter-national, Wallingford, UK, 2000.
Horse evidence supports Darwin-Wallace
evolution by an infinite number of small
changes through millions of years. Welcome
macroevolution, even though it is absent in
horses! “Sports” by breeders fit
macroevolution—giant steps! Equine
paleontology strongly supports classic
microstep evolution as put forth by Ronald
Fisher (1930), thousands of other biologists
and the educated public. .In paleontology, the
horse is by far the best documented mammal.
Regardless, Hollywood puts the Roman army
on horses when they only had ponies!
The horse sequence from early Hyracotherium
(4 toes on each front foot, 3 on hind feet) to living
Equus traces the loss of toes, skull changes and
size increases that characterize horse evolution.
Vestiges of the first & second toes still exist as
splint bones on the cannon bones. The evolution of
modern horses is linked to the spread of grasslands
in the late Tertiary epoch. Equus arrives 4 million
years ago, the genus of all modern equines. The
evolutionary aspects were first worked out in the
late 1800's and involved people like Thomas
Huxley. The evolutionary sequences provides the
most classic example of dramatic longterm
evolutionary change within a lineage with the rise
and fall of branching species, one replaced by
another..
When paleontologic horses started to
become runners, there was a
simultaneous increase in body size,
leg length and length of the face. The
bones of the legs became fused
together. The leg bones and muscles
became specialized for efficient
to-and-fro strides, without flexible leg
rotation. Horses stood on tiptoe thus
adapted for speed. Their weight was
supported by elastic ligaments that ran
under the fetlock to the big central
toe (coffin bone).
Speed depends mostly on the integrety
of the legs. In the illustration of Bull Lea
you see that his front tendons are a little
bowed. Overexcercise must lead to
inflammation such as inflammation of
the suspensory tendons. A bowed horse
had muscles SO STRONG that they
uprooted the ligaments from the bone.
Of course, these suspensory tendons will
reset, yet not as good as new.
Order Perissodactyla, Family Equidae,
Genus Equus
The taxonomy of horses, donkeys and zebras is
a start for genetics as the study of the earliest
equids is another and anatomy another.
Equus burchelli, the Plains zebra of Africa
Equus zebra, the Mountain zebra of South
Africa
Equus grevyi, Grevy's zebra, the most horselike zebra.
Equus caballus, the true horse, which once had
several subspecies.
Equus hemionus, the desert-adapted onagers
of Asia & the Mideast, including the kiang
Equus asinus, donkeys of northern Africa.
The real environment
Fixed races, scandal, insurance fraud, high
finance in the millions of dollars and
murders like the Woodward accident mark
the horse industry and the millionaire
horsey set. Certainly, a few progeny have
“replaced” sires—perhaps the teaser.
Horse games are a form of entertainment,
chisling and bribery in which the servants,
stealing what they can, perform for royalty
possibly in the present form of moviestars
who have replaced many of the millionaire
families of a century ago. This much is
clear.
Genetics starts here
Even sires like Native Dancer, pulled in
the Kentucky derby!, are inbred. The
antique suggestion is “Breed the best
with the best,” yet good performers arise
at random—often. The reason that there is
no real trend in most sires is that they are
rather close to being copies of each other.
Talk of compatability, doses, nicks, line
breeding and so on is only part of a
mystique.
Bull Lea, the sire of Citation. His
uncle was Sir Gallahad III.
When the rank of the horse is compared to
the year, no correlation is derived.
This means that the breed has not improved in
100 years, despite Secretariat being rather
remarkable. One can add that Hancock,
Woodward Senior and others paying $125,000
to import the sire Sir Gallahad III in the 1920s
reinforced inbreeding through breeding the best
with the best..
This—at random—is a rather strong statement,
disturbing for the little old ladies who are pouring
over horse pedigrees as if they were founding a
new religion. Do you expect the greatest
performer Secretariat also to have been the
greatest sire or grandsire or specialist broodmare
sire? Things don’t work that way, do they ?
Plucky Liege was one of the most important
broodmares of the 20th Century. Two of her
sons, Sir Gallahad III and Bull Dog were
leading sires in America, and 2 others, Bois
Roussel and Admiral Drake were sires of
classic winners in England, Ireland and
France. Plucky Liege produced 12 foals in all,
11 of which were winners, and 6 of which
won stakes, including 2 classic winners. Five
foals were sired by Teddy.
As so common, a leading broodmare sire Mr
Prospector 1970, Raise a Native out of Gold
Digger by Nashua has Teddy on the male and
female lines of his pedigree.
ACE, the angiotensin converting enzyme
This enzyme has the hilarious speed gene that
never will prove out.. Nonetheless, ACE is
much better than nothing, though quite
out-of-place since it is studied as relating
to hypertension and myoinfarctions in
humans. Sports medicine is not yet
extended to racehorses. This gene is
involved in human arteriosclerosis and
hypertension. Someone of bottomless
ignorance has confused blood pressure with
the functionality of the legs as limiting for
SPEED in racehorses.
From quite a different view, all variables
of all kinds are testable very easily in
every race, fixed or unfixed. Run the
horse races in analysis of variance
(ANOVA). The problem here is different:
finding insertion/deletion polymorphisms
in ACE genes in horses that do indeed
have distinct athletic abilities. Can genetic
and environmental risks be told apart in
relation to cardiac difficulties such as the
mitral valve problems in certain few
horses? We’ll wait and see.
Nasrullah, sire of Bold Ruler the sire
of Secretariat.
The impression is that the enormous
nucleotide sequencing power of today’s
genetics is going to be used to rip off the
breeders that are foolish enough now to
pay $150,000 stud fees for carboncopy
stallions. The Sittingbourne Research
Centre in Kent, UK offers DNA screening
tests that identify specific characteristics
relating to trainability, performance and
soundness, even identifying optimum
track distances for individual horses. Isn’t
that nice?
What is Bull Lea telling us? Legs not lungs.
He was bowed in BOTH legs. Speed causes
some loss of function, yet of course not his
“best sire” genetics. ACE came over from
human sports medicine. Do those people need
hypertension ? ? ? At this point please note
that emboli floating about are likely to be
filtered out BY THE LEGS. The danger for
horses seems to be the ignorant and
fraudulent nature of the ACE promoters.
The forelegs are like puppets on strings pulled
from the shoulders. That pull is so very great,
it can pull the ligaments off the bones.
Blood volume expansion together with muscle
movements and increased intrathoracic
pressure, supplements venous return and
increases atrial and myocardial fiber
stretching and pressure. Exercise increases
the plasma levels of many hormones like
endorphin, arginine vasopressin, cortisol,
catecholamines and the hormones of the
renin-angiotensin-aldosterone system,
especially ACE. These are hormones involved
in the control of cardiovascular function and
fluid balance as well as with stress and relief
from pain. See ”The ACE gene and muscle
performance,” Nature, vol. 403, p. 614, 10
February 2000.
To understand how variations in the ACE gene
might influence how you run, you need to
know what ACE does. Angiotensin is present
in the blood. Under certain conditions, the
kidneys secrete the hormone renin into the
blood which cleaves a 10-aminoacid protein
from angiotensinogen to form the compound
angiotensin I. ACE can knock 2 aminoacids
off angiotensin I to form angiotensin II.
Angiotensin II has several functions.
It directly increases blood pressure by
constricting arteries. It indirectly raises blood
pressure and blood volume by stimulating the
thirst centers in the brain and directing the
kidneys to conserve more minerals and water.
Altering vascular tone considerably
influences blood pressure.
ACE inhibitors relate to lowering
hypertension and reducing heart failures.
Their beneficial effects can be attributed
to blocking the production of angiotensin
II from angiotensin I.There are alternative
enzymes capable of converting
angiotensin I into angiotensin II like
chymase. Many OTHER FACTORS like
bradykinin as a vasodilator are involved in
controlling the circulation like pulse rate
and air flow respiration. Certainly, more
than one gene calls for investigation !
What else do we need to know? The pulse
and the arterial saturation percent of
OXYGEN. These variables (never reported! ?)
by oxymeter are common to human and NOT
to veterinary medicine. Incidentally, red
blood cells can be both nutritionally and
hormonely increased. That is packed cell
volume can be most easily tested. AGAIN,
deworming helps. Many variables are easy to
obtain continuously. Treadmills and various
other devices, variables and tests are used
little.
The inhibition of ACE reduces
hypertension.
What the speed gene people are saying is
that if the heart works even harder, more
races will be won. Will the ligaments fly
off the bones before the heart attacks ?
What is human and what is equine and
what is normal and what is pathologic are
being confused by people who just don’t
know. More: much information is missing.
Is ACE an undetected racing dope ? Or
better: Would it work? You can bet it’s
been tried unsuccessfully in horses. When
will ACE reports on humans from the
Athens Olympics be available ?