British Breeder Magazine May 2021

Feature Article - DNA
carriers, which brings a 25% chance of
breeding an affected foal. These tests
look for a specific single gene that is
responsible for the problem. Recently,
Warmblood Fragile Foal Syndrome
(WFFS) has received much attention
in the press. It is caused by a mutation
in the gene responsible for collagen
biosynthesis. WFFS causes lesions and
malformations of the skin in neonatal
foals, who are unable to survive. To find
this mutation, testing needs to drill down
to SNP level. It will not show up in the
STR parentage tests currently performed
as part of equine passporting.
While diagnostic tests are reliable in
testing for an individual disease, by
telling us if a horse or pony is or is not a
carrier of a particular mutation, it is quite
cumbersome, and expensive, to have to
run individual additional tests for each
possibly relevant genetic mutation that
could affect our breeding programmes.
SNP profiles – depending on their
design – can, on the other hand, show
tens of thousands of pieces of
information at once, thus providing
parentage verification and all this
additional information in one test.
The potential of SNP profiles goes
further. Not only can they be used for
showing up known conditions, but they
could also help us identify further
correlations between genetics and
known problems that can affect a breed
in future by allowing us to identify
patterns between the occurrence of the
problem and commonalities and
differences in SNP profiles of affected
and not affected animals.
Experienced breeders already know,
for example, that laminitis and EMS
seem to be running in particular families,
with some ponies affected, when others
develop no issues, with the same
management. Studies are already
underway to help us identify which
genes may be responsible for a
predisposition for this problem, but much
more work, and much more SNP data,
is needed. The potential for welfare
improvement is obvious: if we know
that a pony is genetically more likely to
contract laminitis, we can prevent the
problem occurring through management.
One word of caution: While the potential
of this is very exciting, we need to be
very careful about how we use the
information it provides. For a start, in
diseases like laminitis, the genetic
component is always going to be only
one of a range of factors. There is a
danger that owners and keepers would
think themselves “safe” from laminitis if
their pony tested free from the genetic
component, and as a result take their eye
off the ball. Secondly, we may
experience unintended consequences,
such as a narrowing of the gene pool, if
certain, otherwise valuable lines, are less
likely to be used due to an
association with laminitis. Quite often,
problems occur because we unwittingly
selected for them over the centuries,
because they were also associated with
desirable attributes.
What this tells us that while DNA testing
and genomic selections can be powerful
tools in battling disease and improving
welfare, we need to use them
responsibly and ensure breeders and
owners are well informed about their
potential, but also about their limitations.
Selection for Desirable Attributes
While the benefit of screening against
potential diseases and conditions is
obvious, we can also think about
Genetic Analysis in terms of
specifically selecting for positive
attributes. This can be achieved by
comparing our physical observations of
equines (their “phenotypes”) with their
SNP profiles, and again by looking for
patterns and correlations.
In horseracing this has famously already
been achieved in the identification of the
“speed gene” Myostatin. Admittedly,
racing is a sport in which success can
easily attributed to quite a narrow range
of factors (speed, distance), whereas
other equestrian sports have a more
complex range of requirements.
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