| dc.description.abstract | The aim of the study was to perform a review study regarding the current genetic background
of OC in the domestic horse. OC is a commonly seen locomotor disorder in young horses
(WITTWER et al, 2007). The cause of OC is still not clear, even though it is assumed that it is
of multifactorial origin, affecting many breeds and with an important genetic aspect. The
whole equine genome scan was the first step in the investigation of genomic areas holding
genes for OC and OCD. During the last years several studies has been done regarding the
genetic background of OC in horses. In some reports it has already been proven that it's a
disorder carried on many different genes (WITTWER et al, 2008).
The articles analyzed for QTL mapping were mostly studies from the University of Hannover
done between the years 2000-2010. The first article was the; Genome scan for Quantitative
Trait Loci for OC in Hanoverian Warmblood horses using an optimized microsatellite marker
set by LÖHRING (2003). LÖHRING revealed; 27 chromosome-wide QTLs on thirteen
equine chromosomes for the OC trait in Hanoverian warmblood horses. In Dierks study 19
chromosome-wide significant QTLs were reveled on 17 equine chromosomes. They were
found on equine chromosome; 2, 3, 4, 5, 7, 8, 9, 13, 14, 15, 16, 18, 19, 21, 22, 24 and 30.
In 2009 Lampe did a complete genome scan in Hanoverian Warmblood horses and refined the
QTLs for OC on chromosome 5, 16, 18 and 21. The genome-wide significant QTLs on equine
chromosome 5, 16 and 21 were as earlier mentioned for fine mapping, together with the
release of the horse genome assembly EquCab2 it was possible to identify new
microsatellites. All QTLs on theses chromosomes were confirmed. Equine chromosome 18
was investigated as well, earlier QTLs on this chromosome was only confirmed in South
German Coldblood horses in a linkage study for OC (WITTWER et al, 2007), and now a
further investigation was done in Hanoverian warmblood horses. A new QTLs was identified
on chromosome 18, thanks to the new microsatellites which made a more evenly and denser
distribution marker set. The genetic influences of the development of fetlock OC and hock
OC did not show any similarity, due the hock QTL did not map at the fetlock QTL. This was
assumed likely as the genetic correlation between fetlock OC and hock OC were close to zero
in trotter horses (GRØNDAHL and DOLVIK 1993) and even negative in Hanoverian warmblood
horses (STOCK et al, 2005)
WITTWER preformed a whole genome scan to confirm the QTLs identified in Hanoverian
warmblood horses in South German Coldblood. A scan was preformed in 216 coldblood
using 250 polymorphic microsatellite markers. WITTWER identified 17 putative QTLs on 17
equine chromosomes for the OC / OCD traits. The aim of WITTWER’s study was to confirm
the QTLs by using single nucleotide polymorphisms (SNPs) of these genomic regions.
SNPs are used as genetic markers for large scale genetic mapping projects and have been used
with good result to identify chromosome regions associated with polygenic human and animal
diseases. In 2008 a commercial SNPs microarray became available, the Equine SNP50
Genotyping BeadChip. It makes it possible to do, genome-wide analyses, quantitative trait
loci identification and validation. It enables the development of a DNA test that can determine
a horse’s genetic risk for susceptibility to a genetic disease, improving horse breeding
programs since it enables the development of new diagnostic methods to upgrade equine
health and welfare.
The aim of KOMM’s study was to make a refine mapping of the already identified QTL on
equine chromosome 2 and 4 in Hanoverian warmblood horses using dense marker sets, and
also identify new potential candidate genes. Another aim of KOMM’s study was to confirm
already identified QTLs and to detect new potential QTL by doing a whole genome scan with
SNPs using the newly developed equine SNP50 BeadChip. 154 unrelated Hanoverian
warmblood horses were used in the whole genome scan. 313 significant associated SNPs for
the different phenotypic traits were observed. The QTL on equine chromosome 2 was
confirmed at 17.55Mb and on equine chromosome 4 two QTL were revealed (at 7.61Mb and
39, 26 MB) these two QTL were located within the same QTL as identified before. In total ten
new QTL were detected on equine chromosome 3, 5, 7, 16, 19, 20, 22, 26 and 29. | en |
