OCTOBER 2023 VOLUME 32, NO.4

A PUBLICATION BY: THE UNIVERSITY OF KENTUCKY DEPARTMENT OF VETERINARY SCIENCE,
MAXWELL H. GLUCK EQUINE RESEARCH CENTER
FUNDED BY:
EQUUS / STANDARDBRED STATION, INC. M&J INSURANCEIN THIS ISSUER E SE A R C H SPOTLIGHT

INTERNATIONAL

The impact of short-term transportation stress
Third Quarter 2023
P. 2,3on endocrine and immune function in horses.
Recent advances in lameHorses are routinely transported for equestrianness detection andlocalization in the horse P.4,5 events as well as medical care. It is well recognizedthat long-distance transportation is a risk factor
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for the development of pleuropneumonia. Results
Equine neuroaxonal
from a nationwide survey showed that horses
dystrophy / equine deare most commonly trailered short distances ofgenerative
myeloencephalopathy
P. 5,6 three hours or less. The Adams Lab at the Gluck
Equine Research Center within the University of
NATIONAL/KENTUCKY
Kentucky Martin-Gatton College of Agriculture,
Why do we need genomes
Food and Environment is currently working toand how do we use them? P.7 investigate the impact of acute transportationstress on immune function in different groupsof horses. Previous research has shown thatT H ANK YOU S PON SO RS!
transporting horses one to three hours can elicit
a stress response as seen through increased heartrate. Our lab has previously shown that shortterm transportation stress can cause changes inwhole blood gene expression of cytokines in aged
horses. Following these findings, we wanted toknow if similar responses occur in young horses.
Additionally, since horses are often transported
to veterinary clinics for diagnostic testing, wehave investigated the effect of transportation
on endocrine responses and testing for insulin
dysregulation.
Two studies where horses were transported one
and one-half hours (55 miles) round trip were
performed. Study #1 focused on evaluating
age-differences in stress and immune response
following short-term transportation. Horses weregrouped by age with six horses in each group.
Group one had an average age of two years old
and group two an average age of 22 years old.

Study #2 evaluated differences in endocrine
responses to transportation between seven insulin
dysregulated (ID) and seven age-matched noninsulin dysregulated (non-ID) horses. For bothstudies blood, saliva, heart rate and temperature
were collected before and after transportation.
Transportation stress led to various physiologicalchanges in both studies. For both studies,
heart rate and cortisol increased in response totransportation, with the highest heart rates recorded
at loading and both serum and salivary cortisol
being highest directly after transport. There were
no differences based on age or whether a horse
was insulin dysregulated. In Study #1, all horses
had increased ACTH following transportation,with three out of five aged horses having ACTH
concentrations above the cutoff for pituitary parsintermedia dysfunction (PPID) 15 minutes after
transportation. While rectal temperature was not
influenced by short-term transportation stress ineither study, these studies were conducted in mild
weather during the spring and fall.
Study #1 also showed increased gene expressionof the pro-inflammatory cytokine IL-6 posttransport in aged horses and increased salivaryIL-6 in aged horses compared to young horses.
Additionally, aged horses had increased cytokine
production from lymphocytes compared withyoung horses. These results are all indicative of theolder horses being in a state of “inflamm-aging”
where they have increased inflammatory markers,
putting them at higher risk for development ofdiseases.
Serum insulin was measured in both studies. In
Study 1, insulin was increased one to three hours
post-transportation in aged horses and followed asimilar trend in ID horses in Study #2,

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although not statistically different from pretransportation insulin levels. In Study #2,
performing an oral sugar test (OST; current
standard for diagnosing ID in horses) posttransportation caused insulin concentrations tobe above the recommended diagnostic cutoff forinsulin dysregulation in non-ID horses and were
twofold greater than pre-transportation OST
results in some ID horses.
The results of these studies show that there are
significant changes in immune and endocrine
function following short periods of transportation.
Additionally, caution should be used when
performing endocrine testing for metabolic
diseases post-transportation as ACTH and insulin
may be elevated in horses without endocrine
disease. It is recommended that ACTH should
be collected for PPID testing at least 30 minutes
after transportation. Furthermore, performing
an OST with in the first few hours following
transportation could lead to inaccurate diagnostic
findings, particularly in non-ID horses. Given theimportance of PPID in the aging horse population,
we are currently evaluating if short-termtransportation stress alters endocrine function anddiagnostic results of horses with PPID and plan toreport on those findings in the near future.
Erica Jacquay, PhD Student
Gluck Equine Research Center
Supervisor: Dr. Amanda Adams

2 | EQUINE DISEASE QUARTERLY

Third Quarter 2023

International report on equine infectious
diseases.
The following report was composed withinformation provided by laboratories in
Lexington, Kentucky, the University of Kentucky
Veterinary Diagnostic Laboratory and by Equine
Diagnostic Solutions, Inc. We are also grateful to
IDEXX laboratories, Germany, for sharing theirquarterly PCR respiratory panel results with thiscommunity.
We included information from the International
Thoroughbred Breeders’ Federation; theInternational Collating Centre in Newmarket,
United Kingdom; and from the American
Association of Equine Practitioners’ Equine
Disease Communication Center. This report isretrospective and does not claim to be complete.
However, it provides an indication of heightened
activity of several considered relevant contagious
or environment-linked diseases among equids.
To further improve this data set, we encourage
everyone in/outside the United States to reportlaboratory-confirmed (toxico)infectious diseaseof Equidae to the ICC in Newmarket, UK, or
EDCC, USA.
We received a single report of Hendra infection ina horse from Australia. Libya reported an outbreakof Equine Influenza on a premises south of Tripoli.
Summer and early Fall is typically the season wheremosquito-borne diseases are more prevalent.
Hence, cases of Eastern equine encephalitis virus
infections have increased. What is worrisome isthat there is increased reporting of EEE from theMidwest United States and from eastern Canada
provinces (12 cases in Ontario). Summer is also
the season for West Nile virus infections. BothEEEV and WNV infections are known causesof clinical neurologic disease in horses. During
the past quarter, we witnessed a surge of equine
WNV cases, particularly in the Western UnitedStates. The surge began with cases in Colorado’s
more densely populated Front Range; followedby unusually high numbers reported from theneighboring states of Wyoming, Nebraska, Utah,
Idaho and Montana. Additionally, California
reported a surge of clinical WNV cases. Many
affected horses were unvaccinated or ‘notcurrent’ on their vaccinations. France (Europe)
also reported WNV cases, while other parts ofEurope with endemic WNV have not yet provided
information.

EQUINE DISEASEQUARTERLYEDITORS
Rebecca Ruby
Lutz Goehring
Allen Page
STAFF
Holly Wiemers
Hendri Smeenk

I N TE R N ATIO N A L
North America reported scattered cases of EIA
positive horses, with six unrelated cases in Texas.
In Europe, France and Italy reported incidental
EIA cases.
Canada reported an outbreak of Equine Arteritis
virus on a stud farm in the province of Prince
Edward Island, where a number of newborn foals
apparently died of (interstitial) pneumonitis.
North America and Europe (France, Sweden and
Switzerland) reported Strangles (Streptococcus
equi spp. equi) cases and outbreaks in several
locations. It is currently the most consistently
reported pathogen for both continents. For
North America, the majority of cases have beenreported from several distinct regions. For theUSA, hot spots have been Florida, Michigan
and Washington. For Canada, reports primarily
originated from the Province of Ontario. There
have been a few reports of Equine Influenza
outbreaks/cases in the UK, France, Sweden and
the Netherlands.
We already mentioned the EI outbreak in Libya.
USA reports two EI outbreaks, one in the PacificNorthwest and one in the Mid-Atlantic region.
Few equid alphaherpesvirus respiratory infections(fewer EHV-1 than -4) were reported from
North America and continental Europe. A single
abortion caused by EHV-4 (Europe-France) and
two isolated cases of EHV-1 neurologic diseasein North America (with the remainder of the herdin quarantine) were reported.

Vesicular Stomatitis virus (Rhabdoviridae)
infections in horses in the USA have not been
contained. New cases were reported from
California, Texas and Nevada, although thenumbers are decreasing.
Miscellaneous:

A case of Rabies infection was reported from
Oklahoma, USA.
Kentucky laboratories and the laboratory inGermany reported high incidences of Strep. equi
spp equi and EHV-4 positive samples with positive
EHV-1 samples submitted on rare occasions.
EDS (Kentucky) reports a moderate number of
EI positive samples with origin from the Eastern
United States, while there were no EI reports fromthe German laboratory. UK-VDL (Kentucky)
reported three samples positive for Equine Viral
Arteritis; however, there is apparently no link to
the EAV outbreak in Canada.
Lutz Goehring
University of Kentucky
Gluck Equine Research Center – Department
of Veterinary Sciencel.goehring@uky.edu

Material published in the
Quarterly is not subject
to copyright. Permissionis therefore granted toreproduce articles, althoughacknowledgment of the source
and author is requested.
Maxwell H. Gluck
Equine Research Center
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
gluck.ca.uky.edu

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Recent Advances in LamenessDetection and Localization in the
Horse

Many horses are affected by lameness each yearwith a large number of these horses being examined
and treated by veterinarians. According to the2015 USDA National Animal Health Monitoring
System (NAHMS) study on equine management
and select equine health conditions in the UnitedStates, 67% of horse operations reported one ormore lame horses within the past year. In thissurvey, about 60% of lame horses had lamenessexamination performed by a veterinarian. Low
grade lameness is usually of less concern to horsesthat perform lower levels of athletic function;although, early detection and identification of thecause of low level lameness can lead to earlier
treatment, resolution of lameness and return toprevious function. Low grade lameness is moreconcerning in horses that perform at speed (i.e.,
racehorses), jump over large obstacles overuneven footing (three-day event horses) or workover extended distances (i.e. endurance horses).
Low grade lameness may indicate the beginningof a larger problem, and if untreated, could leadto a catastrophic injury, which could result in endof career or end of the horse’s life. Thus, goodscreening tools are needed to identify early, subtle
lameness to prevent low grade injury/lamenessfrom developing into a catastrophic injury.
The mainstay of lameness and musculoskeletal
injury diagnosis begins with a complete
lameness evaluation. However, agreement among
veterinarians on the affected leg and degreeof lameness is poor for horses with low gradelameness. Within the past 20 years, horse mounted
gait analysis devices have been developed andhave been shown to have better accuracy in theidentification of low grade lameness compared tovisual examination by experienced veterinarians.
Benefits of these systems are ease of use and theability to be used on the farm.
The Lameness Locator® is one of the first of thesesystems developed. It is an easy to use, accurate
system that is currently used by veterinarians
around the world. This system is composed ofthree small sensors that can be easily attached tothe horse and provide real-time information abouta horse’s lameness, by identifying asymmetrichead and pelvis movements. This system has theability to record type of footing and can makecomparisons between trials, such as before andafter flexion tests and/or blocking.

4 | EQUINE DISEASE QUARTERLY

More recently, additional horse mounted motion
analysis systems have been developed. Twosuch systems are the Pegasus® system andEquiMoves®, both of which were developedin Europe. While these systems are newer, they
provide some of the same symmetry indices of
the head and pelvis as the Lameness Locator®
system. In addition to evaluating movementsof the head and pelvis, these two systems also
allow evaluation of limb movement since theyalso include limb mounted sensors. For instance,with the Pegasus®, hock range of motion canbe measured. Protraction and retraction, as well
as abduction and adduction of all four limbs
can also be determined with these systems.
Even more recently, the use of artificial intelligencehas provided even more advancements in equinelameness detection and monitoring. A videobased system has been developed for use on asmart-phone, which is called Sleip. This is a
subscription based program for veterinarians thatallows horse owners to upload videos to a cloud
for analysis. This system provides the opportunity
for objective follow-up in horses without the needfor sensor application.
In addition to improvements in objective lamenessassessment, which allows regionalizationof lameness, there have also been recent
improvements in diagnostic imaging tools that
can help with localization of lameness to specificbony and soft tissue structures. Within the past
decade, computed tomography has been adaptedso that it can be used in standing horses. A CT
scan provides 3D imaging of a section of thehorse’s body. This type of imaging provides more
information about bony structures compared tostandard radiographs and with contrast injection,
can also be used to image soft tissue structures.
The standing CT scanners now available havethe same high resolution as previous CT scanners
that were only available for use under generalanesthesia. Additionally, these new standing CT
scanners can be safely used to obtain 3D imagingof the horse’s limbs from the level of the carpus(knee) and tarsus (hock) down through the foot.
In addition to standing CT, positron emission
tomography scan is becoming available in horses,
which can also be performed in the standing
horse. PET allows functional information aboutbone and/or soft tissue structures within thescanned area, which can indicate if an imaging
abnormality is currently active.

Material published in the
Quarterly is not subject
to copyright. Permissionis therefore granted toreproduce articles, althoughacknowledgment of the source
and author is requested.
Maxwell H. Gluck
Equine Research Center
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
gluck.ca.uky.edu

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The PET scan is performed after a radioactive
tracer is administered intravenously, similar toa bone scan. The PET scan is combined withanother type of imaging (typically MRI or CT)
so that the radioactivity can be matched up withspecific anatomic structures.

Equine neuroaxonal dystrophy / equine
degenerative myeloencephalopathy

These advances in lameness detection andlocalization will aid equine veterinarians in early
identification of disease processes in horses,
which will advance equine welfare, minimize
catastrophic injury and prolong the athletic
capabilities of horses.
Valerie J Moorman, DVM, MS, DACVS-LA,
PhD
Clinical Associate Professor
Large Animal Surgery and Lameness
University of Georgia
College of Veterinary Medicine
Athens, GA
valerie.moorman@uga.edu

Equine neuroaxonal dystrophy (eNAD) andequinedegenerative
myeloencephalopathy(EDM) have become some of the most common
postmortem diagnoses in neurologic horses in
the United States. They are two diseases that
can have identical clinical signs, with bothconditions involving degeneration of the central
nervous system. They are distinguished by thelocation within the central nervous system that
this degeneration occurs, as eNAD affects thebrainstem (specifically the medulla), and EDM
affects the spinal cord in addition to the brainstem.
The clinical signs associated with eNAD/EDM
can be variable, but most commonly involve anelement of proprioceptive ataxia (incoordinationof limbs), and, described more recently, signs
may also be accompanied by behavior changes.
The ataxia is typically symmetric and often has aslower onset, as opposed to beginning suddenly.
The severity of the ataxia is most often mildto-moderate. The behavior changes observed
can range significantly from the horse seeming
more quiet-to-dull, all the way to a horse thatis extremely excitable and not one the owneror trainer can claim to behaviorally recognize.
Many owner accounts describe a “switch flip” insuch horses. The behavior changes may be noted
under saddle and/or when handling the horseon the ground. In some cases, descriptions ofchanges in herd behavior, inter-horse aggression
or bouts of unpredictability and explosivity havebeen reported.
Reasons for the development of eNAD/EDM are
not fully understood, but may involve a variety ofgenetic, nutritional and/or environmental factors.
The disease can affect many breeds and a variety
of ages. While younger horses (less than 12
months old) were historically the classic age-ofonset description, more recently at the author’s
institution, 5-15 years of age and predominantly
Warmblood breeds seem overrepresented(unpublished data). Data suggest that deficiencies
in antioxidant vitamin E may play a role in thedevelopment of eNAD/EDM, but the underlying
mechanisms remain to be fully understood. Some
horses that are diagnosed with eNAD/EDM have
low blood vitamin E levels, but it is also possiblethat the vitamin E deficiency associated with thedisease could have occurred early in the horse’s
life or development, even if their blood levels
are normal at the time of evaluation. Researchis ongoing to better understand this aspect ofeNAD/EDM.
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Unfortunately, at the time of this publication,
eNAD/EDM does not have an available, definitive
diagnostic test that can be performed in the living
horse to confirm its presence. eNAD/EDM can
only be diagnosed postmortem via microscopic
evaluation of the brain and spinal cord by anexperienced pathologist. This means that eNAD/
EDM is a “diagnosis of exclusion” in the living
horse. Put simply, we are tasked with trying
to ensure that there are no alternative diseases
that may be contributing to the clinical signs ofconcern. In horses that we suspect have eNAD/
EDM, if we are able to “rule out” these alternative
diseases through diagnostics and observations,
we are left with an increased suspicion of eNAD/
EDM which we then term our “working diagnosis”
until it can be confirmed postmortem.
The clinical signs observed in horses with
eNAD/EDM are often similar to those seen
in other neurologic conditions; ataxia iscommonly attributable to cervical vertebral
stenotic myelopathy (CVSM, colloquiallyknown as Wobblers), or equine protozoal
myeloencephalitis (EPM), two conditions which
are also frequently diagnosed in neurologic
horses in the United States. Determining if
a horse has CVSM is best approached using
imaging (radiographs, myelography, computed
tomography). Determining if a horse has EPM orother infectious diseases is most comprehensively
approached through analysis of cerebrospinal
fluid (CSF) and blood, where CSF is obtained
through a spinal tap. Importantly, other causesof unpredictable and abnormal behavior as well
as gait abnormalities should be considered (i.e.
musculoskeletal sources of pain, like lameness,back pain or muscle diseases; equine gastric ulcer
syndrome, among other sources of discomfort
and reactivity). Your veterinarian will use acombination of history and examination findings
to determine the most likely possibilities andformulate an appropriate diagnostic plan.

6 | EQUINE DISEASE QUARTERLY

If alternative sources for the ataxia and behavior
change in eNAD/EDM suspect horses have been
ruled out, horses with this working diagnosis havea variable prognosis. Some horses will stabilize
in their ataxia and/or behavior abnormalities formonths-to-years without progression. Still others
will progress in their signs. Recommendations
are made based on the severity of disease andare generally limited. Depending on risks tosafety of the horse and/or his handlers, a tailored
exercise plan may be recommended or thehorse may need to be retired from riding. Those
horses with severe clinical signs may pose asafety hazard to themselves or their handlers andultimately require euthanasia.
In conclusion,
eNAD/EDM is a frustrating spectrum of chronic
neurodegenerative disease currently without
antemortem confirmatory diagnostics, making it
challenging for the horse, the horse’s connectionsand veterinarians alike. Research is ongoing into
understanding the pathophysiology, diagnostics
and, hopefully, eventual treatment and prevention
options for these diseases.
Sarah F. Colmer, VMD, DACVIM
Fellow, Large Animal Neurology
Penn Vet New Bolton Center
University of Pennsylvania
School of Veterinary Medicine
Kennett Square, PA
Colms@vet.upenn.edu
610-444-5800

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Why do we need genomes and how do
we use them?

For centuries, horse breeders have chosen to matespecific sires and dams based on information inpedigrees and traits that they find desirable withinthem. The goal of pedigree analyses, and theresulting breeding pair selection, is production of
successful offspring through the propagation of
beneficial genes. Although this has worked well,there are problems associated with breeding within
a closed book that will not be well managed bypedigree analyses. For example, genes associatedwith disease may be selected for when linked todesirable traits. Additionally, inbreeding may
result in important copies of genes being removed
from the population.
The first reference genome for the horse waspublished in 2007. Since then, the equine researchcommunity has been able to use this resource
to catalog genetic variants (called alleles) that
occur in the horse and measure their frequencies
across breeds. This has been a powerful tool for
identifying disease-causing genetic variants.
Additionally, animals who are carriers can be
identified and therefore the passing of these alleles
to the next generation can be managed.
Inbreeding is a practice used to “fix” genealleles that produce the most desirable traits,
removing the copies of the genes that don’t
produce the trait. It is how we create breeds with
distinguishing characteristics. However, there
is a chance that animals can become too inbred,and that many important genes with benefits thatare not as obvious are also purged, resulting inan unexpected increase in less fit animals in the
population.
An inbreeding value quantifies exactly how muchgenetic diversity an animal has inherited. This
number can be calculated exactly with genetic
data. Inbreeding values derived from pedigrees
however are not going to be as accurate. Excluding
the sex and mitochondrial chromosomes, a foal
will inherit exactly half of its genomic content
from its sire, and the other half from its dam.
What is inherited from the respective grand-sires
and grand-dams is going to be roughly 25%, but
not exactly.

This inaccuracy makes pedigree based inbreeding
calculations unreliable for an animal, and byextension for the population. By performing
whole genome sequencing on an animal andquantifying the density of homozygous regions of
the genome (regions inherited from each parent
that are identical at the nucleotide level), theactual measure of inbreeding can be assessed.
Once measured, a rate of change for inbreeding
can be monitored. Although a so-called tipping
point for inbreeding, i.e., when genetic diversity
becomes too low to maintain a healthy populationis almost impossible to assess, changes of rate of
inbreeding can be easily measured and changes inthat rate can be addressed.
Likewise, when a seemingly inherited trait
emerges, whether negative or positive, genome
sequencing is the best tool for identifying the genealleles associated with, and perhaps responsible
for, that trait. This is not to say that it will easily
provide the answers, as many traits are geneticallycomplex in nature, but it is the best approach foranalyzing the genetics of an animal or population
to gain an understanding of the underlying genetic
cause.
Having a reference genome and being able
to inexpensively look at an animal’s genetic
composition is by no means a complete solution
to the genetic problems that affect horse health.
They are, however, essential components among
the resources we need to understand the genetic
basis of health and wellbeing in these animals.
Ted Kalbfleisch, Ph.D.
Associate Professor
Department of Veterinary Science
Gluck Equine Research Center
University of Kentucky
Lexington, KY 40546-0099
ted.kalbfleisch@uky.edu
1-502-424-7795

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