Arabische Pferde IN THE FOCUS 4/2020 (Vol. 24) - public

DNA research in Horses
Bairaktar's acquittal
Wissenschaft
Warmblood fragile foal syndrome (WFFS) has become a
horror in recent years in Warmblood breeding. But because
similar symptoms to WFFS have also been found in (historic)
Arabian horses, research has been conducted whether
or not Bairaktar, who had a significant influence on Warmblood
breeding, was the origin of WFFS.
Warmblood fragile foal syndrome
(WFFS) is a hereditary disease, an
autosomal recessive disorder caused
by a single nucleotide variant, that causes
an incurable connective tissue disorder.
It can be detected immediately after birth,
when the foal usually gives a somewhat
weak impression, but still seems to be okay
with an existing sucking reflex. However,
due to the genetic defect, the skin (epidermis)
is not firmly connected to the lower tissues,
which means that it may tear off even
with only slight contact and stress, such as
when trying to get up. No need to say, that
the foals cannot survive.
Similar disease in 1855
These symptoms sounded very much like a
disease, which was first described in 1855 by
Prof. Adolph Rueff at Hohenheim. In the years
between 1841 and 1853, a „peculiar skin
disease was observed in several foals born at
the Royal Stud Weil in Württemberg: The foals
were mostly born dead, or died at birth or
soon after, and all displayed the same congenital
malformations of the skin and the
hooves. The skin, especially on the legs, but
also on the back, the neck, and the face, was
usually hairless, there were cysts filled with
fluid, the upper skin detached from the layer
beneath, the hooves shrank before birth and
fell off in the womb or shortly after birth,
and the oral mucosa was also affected.”
Based on the description of the symptoms,
we can today identify this condition as epitheliogenesis
imperfecta (EI) or junctional
epidermolysis bullosa (JEB). Professor Rueff
also observed that all affected horses were
grey and descended from the stallion Amurath
I 1829, whether in the first, second, or
third generation. In other words, Rueff identified
the cause as grey colouring, inbreeding,
and descent from Amurath I. He wrote:
„As for eliminating this curse, the obvious
strategy would be to stop using this stallion,
in particular to avoid inbreeding, and in
my opinion this would quickly and certainly
achieve the desired result. However – the
stallion is of such great significance, that it
would be a disaster for the stud if he were
to be so condemned, and it would be highly
regrettable if nature itself would end the disease
by the death of the stallion (who is already
25 years old). Thus, as long as the stallion
lives, it should be considered how the
problem might be solved without resorting
to such very unfortunate radical means.”
Inbreeding brought it to light
We may doubt today if the grey colour is in
any way connected to the above disease, as
this condition today occurs only in Belgian
Draft Horses (chestnuts) and American
Saddlebreds, where it is clearly not linked
to the grey colour. The fact that the affected
horses at Weil were grey is easily explained
by the fact that it was the most common colour
in the Weil herd, especially among the
descendants of Bairaktar and Amurath I.
Rueff’s observation that inbreeding and descent
from Amurath I might be the cause, is
supported by the affected foals’ parentage.
It you examine their pedigrees, you will see
that Amurath’s sire Bairaktar db appears
each time both on the sire’s and on the dam’s
side. There is only one exception, the 1846
foal out of Kaaba II, whose symptoms were
not identical to the others.
We have to remember that in 1855, the
laws of Mendelian inheritance were not yet
known; Gregor Mendel only published them
in 1866. Today we know that EI and JEB are
passed on by autosomal recessive inheritance
(as are CA and SCID); this means that
it is not linked to gender, and both parents
have to be carriers. Carriers appear perfectly
healthy themselves, and only when the
defective gene is inherited from both parents,
making the foal homozygous for this
trait, will it be affected and die. If we assume
that Amurath I 1829 was a carrier, the mares
must have been carriers as well. These
however, with very few exceptions, were not
descended from Amurath I, but from Amurath’s
sire, Bairaktar Or.Ar. In other words,
we may assume that Bairaktar Or.Ar. introduced
this condition to the stud. But it only
manifested itself when his daughters were
bred to Amurath I, making them inbred to
Bairaktar Or.Ar.
Distribution of WFFS
Back to today’s WFFS: A group of researchers
(Reiter, Wallner, Brem from the University of
Veterinary Medicine Vienna, et. al.) investigated
the breed distribution of the WFFS
allele. All in all, 4081 horses belonging to 38
different breeds were screened. In total, 4.9
% of the horses representing 21 breeds carried
the WFFS allele. The affected breeds were
mainly warmbloods, with carrier frequency
as high as 17 % in the Hanoverian and Danish
Warmblood. The WFFS allele was not
detected in most non-warmblood breeds.
Exceptions include WFFS carriers in the Thoroughbred
(17/716), Haflinger (2/48), American
Sport Pony (1/12), and Knabstrupper
(3/46). But all of the 302 Arabians in this investigation
were free of the mutated allele.
Considering the huge impact the stallion
Bairaktar had on Warmblood breeding
through his great-great-great-grandson
Amurath 1881, and the fact that Bairaktar
appears several hundred times in some
Warmblood pedigrees, such as Cornet
Obolensky, Sandro Hit or Valegro, the researchers
wanted to investigate this track
further. They then asked for a tooth of
Bairaktar, to extract and analyze his DNA.
Bairaktar’s skeleton is property of the University
of Hohenheim, is on permanent lease
to the State Stud Marbach and exhibited
at the horse museum at Offenhausen. DNA
extraction was performed in the cleanroom
of the laboratory at the Natural History Museum
in Vienna, following standard procedures
to avoid contamination, using one
of the molars of Bairaktar. The result clearly
showed that he did not carry the mutated
allele. This, together with the fact that all
Arabians in this investigation were free of
the mutated allele, of which 16 mares and
3 stallions were used in the Polish breeding
program and traced to Bairaktar, acquitted
the desert-bred Arabian Bairaktar from
being the origin of WFFS. To date, the exact
origin of WFFS is unclear.
Gudrun Waiditschka
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