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

Genetic Research (II)
Speed and
Endurance
Zucht
In the last issue we looked at the domestication and emergence of the various
horse breeds under new genetic findings. This second part will deal with various traits,
such as the genetic basis for speed and endurance.
Since the domestication of the horse until
today, humans have created a large
number of different horse breeds, which
have the most varied properties, depending
on what their area of use is. It is therefore
not surprising that different horse breeds
also have different dispositions to build muscle
mass. There are short-distance runners
(sprinters) who have to exert high power over
a short period of time and distance, such as
the Quarter Horse, which is bred for 400 m races.
And then there are long-distance runners
(stamina), whose strength is the persistent
muscle work in long races, up to endurance
rides of 160 km.
The gene for muscle growth
The protein myostatin (MSTN), which inhibits
muscle growth, is responsible for the amount
of muscles. If this protein is inhibited due to a
mutation, there is increased muscle growth.
This mutation was identified a few years ago:
the base thymine (T) was replaced with cytosine
(C). If a horse has this mutation (C / C
instead of T / T), the horse has more muscle
power for short sprints. This gene was therefore
called the "speed gene". Accordingly,
there are three different genotypes, and the
following properties have been postulated:
C / C - homozygous for the C allele, these are
the sprinters among the racehorses that have
a high proportion of muscle mass in relation
to the total weight and are suitable for short,
fast races - they are also usually early maturing.
Horses with T / T are homozygous for the
T allele and therefore have the other variant
of the myostatin gene. These are the stayers,
the endurance runners, who are usually lighter,
i.e. have less muscle mass and are more
suitable for long distances - they are usually
also late maturing. And of course there are C
/ T, i.e. heterozygous horses, which are particularly
suitable for medium distances.
The team led by Mim Bower (2012) from
Cambridge University examined different
breeds for the frequency of C / C and T / T. It
turned out that the oriental breeds, which includes
the Arabian horse, had only 3% C / C,
against it 87% T / T, the remaining 10% were
C / T. It looked very different with the English
Thoroughbred. Here, 46% of the sprinters
were homozygous C / C, and only 7% T / T,
the difference again C / T. In the stayers, i.e.
English Thoroughbreds that run over 1800 m
and more, it was only 3% C / C and 35% T / T,
the majority - namely 61% were mixed C / T.
Therefore, English Thoroughbreds could not
have inherited its speed from its oriental ancestors,
especially not on the relatively short
distances (up to 1800 m). So, where did it
come from?
The speed gene
The answer to this was surprising: Apparently,
this mutation was only introduced once
into the gene pool during the founding phase
of the English Thoroughbred, by a mare born
in Great Britain, possibly even a Shetland
pony! In the British Shetland pony, 38% of the
animals examined were homozygous for C /
C, 38% homozygous T / T, the rest (25%) were
mixed. By the way, the highest rate for C / C
can be found at the American Quarter Horse,
the sprint specialist (83% C / C), which was
bred for 400 m races.
The same team of researchers also examined
the DNA of "historical skeletons", namely Thoroughbreds
that were born between 1849
and 1930. Well-known names like Eclipse,
Hyperion, Persimmon and St. Simon were
among them. All 12 animals examined were
T / T. So back then T / T was predominant, today
C / C - how did this shift come about? The
explanation lies in the changed conditions
Apparently the "speed" Mutation
was only introduced
once into the gene pool of
the English Thoroughbred.
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