EQUINE | Equine Disease Update
of epidemiological studies and pedigree analyses to find
common factors among cases.
Hydrocephalus, for example, is a developmental disor-
der that often results in stillbirth of foals and dystocia
in dams. Possible causes of the defect in horses could
not be proven based on field data and pedigree analy-
ses suggested the disorder to be complex. With this in
mind, a genome scan of 82 horses (13 cases, 69 controls)
was performed and a small section of the genome was
identified as containing the cause of the disorder. Ge-
nomic sequencing was then performed on 10 horses (4
cases, 6 controls) and the genetic cause of the disorder
was pinpointed. Ultimately, 2 copies of a mutation that
changed a “C” nucleotide to a “T” nucleotide (Figure 1)
resulted in the disorder.
Although previously believed to be a complex dis¬ease,
genetic and genomic methods were able to prove that
the disorder was in fact simple, leading to the develop-
ment of a genetic test that can help breeders avoid the
disorder. It is important to note the difference between a
genetic test for a simple disease, such as hydrocephalus,
and a genetic test for a complex disease (e.g. osteochon-
drosis). Genetic tests for simple diseases can confirm or
rule out a genetic condition; however, genetic tests for
complex diseases only help to determine an individual’s
chance of developing a genetic disorder—an important
dis¬tinction when genetic tests are used to help make
breeding decisions.
pro¬vide an opportunity to cross certain disorders off
that list, thereby helping to eliminate or reduce the oc-
currence of those diseases.
Contact:
Dr. Brandon D. Velie [email protected]
Department of Animal Breeding & Genetics Swedish
University of Agricultural Sciences Uppsala, Sweden
International Horse Movements and Disease
Risk
The World Organization for Animal Health (OIE) is re-
sponsible ior ensuring transparency of the global animal
disease situation by requiring reporting of occurrences
of animal diseases of eco¬nomic and public health im-
portance by its member countries as well as safeguard-
ing the health and safe trade of animals and animal
products by setting international standards document-
ed in the OIE Terrestrial Animal Health Code (TAHC).
Incidents of disease introduction associated with in-
ternational movement of live horses are sporadical¬ly
reported to the OIE for immediate notification via the
OIE World Animal Health Information System (WAHIS).
From 1995 to 2014, 54 incidents were reported to the
OIE. The immediate notification reports from the Mem-
ber Countries were reviewed in conjunction with other
information available in the public domain to provide
the following analysis.
In either scenario, genetics and genomics in Thorough-
breds have far-reaching potential beyond that of breed-
ing and selecting faster horses. Understanding diseases
caused by a single gene as well as complex dis¬eases
caused by multiple genes and the environment can lead
to early diagnosis and targeted treatments. Equine influenza (13 events) and contagious equine
metritis (12 events) were the most fre¬quently report-
ed diseases. For seven events, the infected horses were
de-tected during post-arrival quarantine and were not
released into importing countries. The 47 other events
resulted in the introduction of pathogens into import-
ing-countries.
While the list of reasons a racehorse never reaches its
potential may seem endless, genetics and genomics Subclinical infections remain a challenge for interna-
tional trade. In 88 percent of reported events, infected
• Volume 19 no 3 • September 2017 •
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