In the last article we discussed how
we can genetically advance a
population of horses based on their
performance traits (in show jumping
and/or dressage). This can be achieved
by selection of the best stallions to
produce the next generation.
Studbooks usually have a policy to
assist breeders who seek this goal by
using a system for stallion approval
and the publication of their breeding
values.
Figure 1. Rousseau (Olympic Ferro x Roemer),
a specialised dressage horse, sire of three
consecutive champions of the KWPN Stallion
Selection in the Netherlands (2006, 2007,
2008). Sire of New Zealand’s Champion
Young Performance Bred Horse of the Year
2008 (Appleton DHU). Foto: Paul Melzer,
courtesy Hassler Dressage, USA.
The next practical question is, can we
achieve genetic progress on multiple
traits simultaneously. In other words,
can we improve show jumping ability
and dressage ability at the same time?
Figure 2. Indoctro VDL (Capitol I x Caletto II),
a specialized showjumper, has been in the top
of the WBFSH ranking for many years (World
Breeding Federation for Sport Horses), and is
still among the stallions with the highest
breeding indexes in the KWPN. Foto: courtesy
VDL-Stud, the Netherlands
To be able to answer this question, we
need to know how these traits
genetically relate to each other, and
we need an estimate of where the
current mare population stands.
Figure 3 is a plot of the breeding
values of all approved KWPN stallions
currently available in the Netherlands.
The KWPN (Royal Dutch Warmblood
Studbook) is used as an example, but
the described principles generally
apply to the other warmbloodstudbooks
as well. The horizontal axis
represents the breeding value for show
jumping; the vertical axis represents
the breeding value for dressage ability.
Every point in the plot is an individual
stallion. The top left quadrant
contains the stallions that are
typically known as dressage stallions
(in blue), and the bottom right
quadrant contains the stallions known
as show jumpers (in red). The top
right quadrant represents the allround
stallions, which pass on
dressage and show-jumping ability
simultaneously. The plot tells us that
most stallions are either in the top
left or bottom right quadrants, and
the number of stallions in the top
right quadrant is quite limited. In
geneticists terms: there is a negative
genetic correlation between
showjumping and dressage ability.
Figure 3. Relationship between breeding values for Show Jumping and Dressage.
This implies that, generally if you
choose to breed with a stallion that
has a high index for dressage, this
would be compromising showjumping
ability, and vice versa. However,
within the sub-population of stallions
with a high breeding index for one
ability there is still quite a bit of
variation with respect to the other
ability, so it is possible to breed a
showjumper without losing too much
in dressage ability.
From the studbooks perspective, the
negative correlation is an awkward
thing to deal with. It means it is more
efficient to use the selection space
(the number of stallions to be selected
each year), on selecting specialized
showjumpers and specialized dressage
stallions than to try and select for
both at the same time. For the
individual breeder it means there is
more choice of stallions if you want
to improve on one trait rather than
both at the same time.
For this reason, the KWPN decided to
opt for specialized breeding directions,
so instead of breeding a generic
"sporthorse". Therefore in the
selection protocol for showjumping
stallions there are no longer
requirements relating to dressage
ability and vice versa. As a
consequence, we can expect that the
graph will change with the blue points
from figure 3 moving further up and
left (showing improved dressage
ability with a decrease in jumping
ability) and the red points moving
down and right (showing improved
jumping ability with a decrease in
dressage ability), as indicated by the
arrows in figure 4. The speed at which
these dots progress will be faster
than if a choice was made to improve
dressage and showjumping ability
simultaneously (the dots moving up
and right).
Figure 4. Stallions identified by type or age: thoroughbred: light blue, 3-6 years: yellow, 7 to 10
years : light orange, 11-14 years: dark orange, 14 years and older: red.
Also on the graph is the bottom left
quadrant with stallions that have a
breeding value below 100 for both
dressage and show jumping, and you
may wonder who these stallions are,
and why they are there since they are
all approved stallions. Many years ago,
thoroughbreds were introduced into
the KWPN population to improve the
old Gelderlander and Groningen
bloodlines, the original base of the
KWPN horse, to produce a better
performing sporthorse. There are still
a number of thoroughbreds approved
within the KWPN to improve certain
mares on type (finer bone) and
temperament (forwardness). These
thoroughbreds are colored light blue
in figure 4. The KWPN selected these
stallions with the expectation that
there would be virtually no loss in
dressage and show jumping ability and
their breeding values were established
once their progeny were competing.
Usually, these stallions had already
proven themselves in international
competition. The plot shows that over
time, the population has advanced in
terms of dressage and showjumping
ability and these thoroughbreds are no
longer needed to enhance the
performance characteristics in the
warmblood population.
We also have to take into account
that when the system of breeding
values was introduced, the KWPN
decided that every year the average of
the population would be reset to 100.
In the previous article we saw that
there is genetic progress in the
population, which means the horses
improve over time, but the scale of
measurement moves equally with
them. This means that the older
stallions with an established breeding
value effectively lose a few points
every year. So also in the bottom left
quadrant we find a high proportion of
older stallions who have lost their
significance for breeding since their
better offspring have been selected to
produce the next generation.
Now that we know the genetic
relationship between showjumping
and dressage, we can give better
consideration to breeding for dressage
or showjumping or both.
The next issue we need to address is
the mare(s) we are to breed from. We
need to know where the mare
population is genetically, where our
mare is in the population, how much
genetic progress do we hope to make
in one generation, in which direction
do we want to make this advance, and
how much we want to spend. This will
be the subject of the next
contribution.