Equine Disease Quarterly | EQUINE
Improved Genetic Selection
The art of breeding horses is based on genetic
selection. Horsemen evaluate visible characteristics
(phenotypes), such as conformation, coat color, speed,
endurance as well as family history (blood lines) and
make breeding decisions based on these evaluations.
As equine breeding has shifted from quantity to
a greater focus on quality, genetics and genomic
research in reproduction has the potential to improve
the accuracy of breeding selection criteria. Research
leading to sequencing of the equine genome has
resulted in the identification of a growing number of
genes that have been linked to positive characteristics
(speed, coat color, etc.) as well as heritable diseases.
These scientific advances are currently used to test
potential carriers before making breeding decisions. If
allowed by the breed registry, pre-implantation genetic
testing of embryos provides a more effective method
to select for (or against) certain genetics. Recent and
ongoing research allows us to recover embryos non-
surgically from the uterus a week after conception
and test the conceptus for the presence or absence of
specific genes. The embryo can be cryopreserved while
molecular genetic testing is performed in the laboratory
and if test results are favorable, it can be transferred into
a recipient mare or even into its biological mother at
a later time. The potential benefit of this technology to
horse breeding is obvious. For example, unless genetic
carriers of a debilitating disease (and potentially also
carriers of some desirable genes) are completely
removed from breeding, selection of healthy embryos
based on pre-implantation genetic testing is the
only way to eradicate the disease. Because of its
practical benefit to horse breeders, the technology
of pre-implantation genetic testing in horses can be
expected to be further developed and gain popularity
as research identifies additional genes that influence
a variety of characteristic of horses, and tests become
available. A related area of expected research intensity
in the near future is investigations on the importance
of environmental influence on gene expression during
fetal development (epigenetics).
Assisted Reproduction
Assisted reproduction is not suitable to all breeders.
However, current knowledge and expected future
research advances in this area offer exciting possibilities
for selective high end breeding operations. Various
assisted reproduction techniques carry some important
advantages with regards to management of both fertile
and subfertile stallions, allowing for treatment of the
semen. For example, frozen and preserved semen can
be shipped anywhere in the world, making valuable
genetics available globally, and preserving genetics from
stallions long after their death. Researchers in Australia
have recently developed a semen extender that allows
for storage of equine semen for an extended period of
time at ambient temperature. This is without doubt a
major breakthrough that can simplify breeding with
shipped semen and reduce some hurdles associated
with timing of the shipment in relation to expected
ovulation. Research advances on semen biology has
also resulted in improved management of stallions
with specific and selective fertility problems. Stallions
that produce ejaculates with poor sperm quality and
viability can often be managed by centrifugation of
their ejaculates and re-suspension of the sperm in
an extender with supportive nutrients. Furthermore,
the quality of an ejaculate can be enhanced through
gradient centrifugation that can separate “good” and
“bad” sperm before insemination. Further research to
enhance our understanding of relevant sperm biology
and advanced diagnostics to identify preferable sperm
populations in an ejaculate is expected to create a
need for robust and efficient technologies to select
superior sperm within an ejaculate.
• Volume 21 Issue 3 | September 2019 •
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