Arabische Pferde IN THE FOCUS Nr. 1/2020 (Vol. 21) - Preview

for racing over the centuries. In the 17th and
18th centuries, the races consisted of a race of
only two horses against each other. The winners
of such a two-horse race had to compete
against each other again, etc. The length of
the races was between 3,200 and 6,400 m. Therefore,
the winner had to be able to run long
distances as well as several races per day. This
required endurance horses (stayers), no sprinters.
In addition, the horses were much older
than today, namely 5 to 6 years old, not two
to three years old. In the late 18th and early
19th centuries, racing changed. The races
became shorter (1,600 to 2,800 m), the horses
younger (three years old) - and this trend has
continued to this day. This also shifted the occurrence
of the T / T genotype in favor of the C
/ C genotype, which was present in the population
at that time, but with a low frequency.
Everyone can think about what this means
for Arab race horse breeding, because here,
too, we see a tendency towards short distances
and towards early mature horses, which
actually selects against the typical Arab characteristics.
It could also explain why it is so
tempting to cross (secretly) English sprinter
blood into the Arab breed.
Other factors
In the meantime it turned out that the inheritance
of speed does not seem to be that
easy. The MSTN test (a genetic test) was started
to predict the suitability of racehorses for
different distances, even before they started
training. But the more horses were tested on
MSTN, the less the predictions were true. Petersen
et al. 2014 was able to show that not
only the CC, TC and TT variants play a role in
racing. Rather, it was realized that in addition
to the mutation of the myostatin gene,
a SINE insertion (i.e. the insertion of DNA
sequences into the genome that are only
100-400 base pairs long) can influence the
suitability for certain race distances. Horses
without SINE insertions are generally long
distance horses, those with one copy are
Milers (their preference is therefore approx.
1600 m), and those with two copies show
up as sprinters. At the same time, it turned
out that in Quarter Horse this phenomenon
is also associated with the proportion of different
fiber types in the skeletal muscles. For
a long time, various types of muscle fibers
in horses have been known. A distinction
is made between types I and II, the former
being held responsible for endurance performance
and occurring more frequently in the
Arabian horse, and type II is standing for the
ability to sprint and increasingly occurring
in the English Thoroughbred and Quarter
Horse - and of course there are mixed types
here too. It is also known that other genes
besides MSTN also influence the composition
of the muscle fiber types. And last but not
least, muscles are not everything, you also
need the will to win!
Effective cooling
To achieve a high level of performance, effective
muscle work is required. One characteristic
of the muscles, however, is that they
produce heat as a waste product, which the
body has to get rid of again - that means, the
body also needs an effective cooling system.
This is done by convection. Convection plays
an important role in physical thermoregulation.
For example, if the body is overheated
by muscle activity, increased sweating and
peripheral vasodilation (widening of the
blood vessels) are triggered. Sweat cools very
effectively by removing heat from the body
through evaporation and thus keeping the
body temperature constant. Basically, however,
the fur significantly hinders the evaporation
of sweat, and thus the cooling. Therefore,
horses have a very special protein in their
sweat, the Latherin. Latherin was discovered
in 1982 and named after the English verb 'to
lather'. It is even a predominant part of horse
sweat because it makes up about 80% of
the protein in horse sweat. Latherin acts like
a kind of surfactant and reduces the surface
tension of the sweat water. The result is that
sweat can wet the oily horse fur much more
easily and consequently evaporate and cool
better. Latherin also creates the foamy sweat
that is visible when the horse works hard,
especially where equipment rubs against the
horse's body.
Samantha Brooks took a closer look at this
protein and found that the Arabian horse has
far more copies of the Latherin gene than expected.
She looked at the number of copies of
the Latherin gene in horses of different breeds
and found that the English Thoroughbred
has four copies, the Arabian purebred even
more. It appears that endurance horses from
southern regions have more copies of Latherin
genes than less athletic breeds that have
historically come from a cooler geographic
region, such as miniature horses, which derived
from Shetland ponies and the Percheron.
But this is a first working hypothesis based on
a small number of horses and further investigations
have to follow in order to be able to
make a conclusive statement.
Incidentally, there are only a few mammals
that use sweat for heat regulation. This includes
the equidae, and here mainly the horse,
the camel and the humans!
Gudrun Waiditschka
Weiterführende Literature - Further Reading
McDonald RE, Fleming RI, Beeley JG, Bovell DL, Lu JR, et al. (2009) Latherin: A Surfactant
Protein of Horse Sweat and Saliva. PLoS ONE 4(5): e5726. doi:10.1371/journal.pone.0005726
Bower, M.A. et al. The genetic origin and history of speed in the Thoroughbred racehorse.
Nat. Commun. 3:643 doi: 10.1038/ncomms1644 (2012).
Ropka-Molik, K. et. al (2019): The Genetics of Racing Performance in Arabian Horses.
Hindawi International Journal of Genomics, Volume 2019, Article ID 9013239, 8 pages,
https://doi.org/10.1155/2019/9013239.
Rooney MF, Hill EW, Kelly VP, Porter RK (2018) The “speed gene” effect of myostatin arises
in Thoroughbred horses due to a promoter proximal SINE insertion. PLoS ONE 13(10):
e0205664. https://doi.org/10.1371/journal.pone.0205664
Meyer, Hanspeter: Funktionelle Genomforschung beim Vollblut (eine Publikation des
Verband Schweizer. Pferdezuchtorganisationen)
Brooks, Samantha (2016) Vortrag anläßlich der WAHO-Konferenz.
Breeding
To achieve a high level of
performance, you need
effective muscle work and a
good cooling system.
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