JULY 2023 VOLUME 32, NO.3

A PUBLICATION BY: THE UNIVERSITY OF KENTUCKY DEPARTMENT OF VETERINARY SCIENCE,
FUNDED BY:

MAXWELL H. GLUCK EQUINE RESEARCH CENTER.
EQUUS / STANDARDBRED STATION, INC. M&J INSURANCEI N T HI S I SSUE

GL UCK RE S E ARCH S P O T L I G H T

INTERNATIONAL
Protective humoral immunity ofSecond Quarter 2023.......................2,3
The ridden horse checklist...............3,4 mares and their foals post equine

NATIONAL
rotavirus A G3P[12] vaccination
Unsanctioned Racing’s Role in Equine
Our research laboratory is interested in
Infectious Anemia (EIA) and Equine
Piroplasmosis (EP) in theunderstanding, treating and preventing equine
United States.....................................4,5
infectious diseases. One of our primary interests
KENTUCKY
is to better understand the genetic and antigenic
Gastroduodenal ulceration syndrome
diversity of equine rotavirus groups A and B. In
in foals in central Kentucky from2020 - 2022...........................................6 addition, we hope to characterize and identify
PLEASE VISIT OUR WEBSITE correlates of protective immunity against rotavirus

infections in horses.

T H ANK YOU SPONSO RS!

Equine rotavirus A (ERVA) globally causes
rotaviral diarrhea in foals and was first described in
1975. Two structural proteins, encoded by P and G
genotypes, are recognized, of which G3, G14 andP[12] are the most common. Swift and intensive
medical treatment typically prevents fatalities
but represents a significant economic burden to
the equine industry. Due to ERVA’s incredibly
infectious nature, the high number of virus
particles shed in fecal matter, its environmental
stability, and the non-enveloped structure, ERVA
is very hard to contain once an outbreak occurs,
which can lead to a heavy burden on farm staff
and veterinarians. Therefore, prevention throughbiosecurity measures, monitoring programs andvaccination is of the utmost importance. Before
the introduction of the monovalent G3 vaccine by
Zoetis in 1996, ERVA infection manifested as adisease of neonatal foals. Mares are vaccinatedthree times during pregnancy at 8, 9, and 10
months of gestation to generate a protective
passive immunity to the foal through colostrum.
Interestingly, rotaviral diarrhea attributable to
ERVA can be observed in foals

between three and four months of age born tovaccinated mares and in neonates of unvaccinateddams. Foals at younger ages are much more
susceptible to infection and develop more severeclinical signs. With intensive treatment, rotaviraldiarrhea has a high survival rate of 94%. However,
without treatment, ERVA can be rapidly fatal,
especially in neonates.
An ongoing collaborative research project at the
University of Kentucky Gluck Equine ResearchCenter is focused on whether vaccination against
ERVA G3P[12] provides cross-protection
against ERVA G14P[12], with an additional
goal of monitoring the duration of maternallyderived protective antibodies. Serum samples
were collected from mares pre-vaccination,
post-vaccination and for multiple months postfoaling. Foal serum samples were collected prior
to nursing and bi-weekly for up to seven months
post foaling. Additionally, fecal swabs fromboth the foals and mares as well as colostrum
and milk samples were collected. A total of 50
mare-foal pairs were included in this study,
leading to a total of more than 1,500 samples. A
virus neutralization assay was used to determine
neutralizing antibody titers in serum against
ERVA G3P[12] and ERVA G14P[12]. Based on
preliminary data, vaccination of mares maintained
and increased ERVA G3P[12] virus neutralizing
titers. Importantly, serum antibodies were crossprotective against ERVA G14P[12]. Further,
ERVA G3P[12] and ERVA G14P[12] neutralizing
antibodies are passively transferred through thecolostrum as pre-nursing neutralizing antibodies
were undetectable and increased greatly in postnursing samples.

JULY 2023 | 1

INTERNATIONAL

Second Quarter 2023
Lastly, we noted that titers of neutralizing International report on equine
antibodies in the foals decreased steadily after birth. infectious diseases.
Work on this project is currently ongoing. Once
serum virus neutralization assays are completed
colostrum and milk samples will be tested using
the same assay to determine the level of transferof neutralizing antibodies from the dam to thecolostrum and from the colostrum to the foal.
Furthermore, RT-qPCR of fecal swabs for ERVA
G3P[12], G14[12] and ERVB will be performed
to identify asymptomatic infections due to natural
exposure during the project period. In future
experiments, we hope to determine the precise
antibody titer necessary for protection against
ERVA beyond the meonatal period.
Lianne Geertrui Eertink, PhD Student
Gluck Equine Research Center
Supervisors: Drs. Feng Li and Dan Wang

The following report was composed withinformation provided by the University of
Kentucky Veterinary Diagnostic Laboratory
and Equine Diagnostic Solutions, Inc. —both in
Lexington, Kentucky, United States of America.
Furthermore, information from the International
Thoroughbred Breeders Federation, International
Collating Centre in Newmarket, United
Kingdom, and American Association of Equine
Practitioners’ Equine Disease Communication
Center was included. This report is retrospective
and does not claim to be complete. However, it
provides an indication of heightened activityof relevant contagious or environment-linked
diseases among equids. To further improve
this data, we encourage entities outside the
USA to report laboratory-confirmed (toxico)
infectious diseases of Equidae to the ICC.
Reports from Asia, Africa, South America andAustralia were not received for this quarter.
The USA reported rapidly spreading vesicularstomatitis virus infections in various cohorts ofhorses mainly throughout California with fewer
outbreaks reported from Texas (first reported in
mid-May 2023). VSV is an arbovirus transmitted
by a varietyof insects, mainly biting midges andsandflies, but also stable flies. Direct contact andfomites are alternative methods of transmission.
VSV outbreaks typically follow a seasonalpattern from late spring and summer in the USA,and reported outbreaks are typically localized to
the Western United States. Typical clinical signs
consist of painful blisters followed by ulcerationof the oral mucosa. Disease is endemic in the
USA and South and Central America.
North America and Europe, including the British
Isles, consistently report strangles (causedby Streptococcus equi spp. equi) cases andoutbreaks. It is currently the most consistently
reported pathogen. In North America, most cases
are reported from several distinct regions. Within
the USA, Florida, Michigan and Washington
frequently report cases, and most cases from
Canada are reported from the province of Ontario.
An outbreak of equine influenza virus was traced
to a Standardbred racing facility in the provinceof Quebec, Canada; the outbreak rapidly spreadto other (mainly) Standardbred training facilities.
On a smaller scale, another outbreak of EI wasreported in the U.S. Pacific Northwest. Scattered
EI PCR positive nasal swabs were also reported
from various U.S. regions,

2 | EQUINE DISEASE QUARTERLYEQUINE DISEASEQUARTERLYEDITORS
Rebecca Ruby
Lutz Goehring
Allen Page
STAFF
Holly Wiemers
Hendri Smeenk

I NT E R N AT IO N A L
from various U.S. regions including the Midwest,
Southwest and East Coast. EI cases and outbreaks
were also reported from central Europe.
Equine herpes virus 4 or 1 respiratory disease
was reported infrequently throughout the USA. A
higher incidence was reported from operations in
the United Kingdom, Ireland and from continental
Europe. Few EHV abortions were reported from
North America. Three abortions caused by EHV-1
were diagnosed in central Kentucky. Of note, there
has not been further propagation of disease within
the pregnant mares on those farms. This is likely
due to high vaccine coverage combined with a fastand effective management intervention. EHV-1
abortions typically occur in the last trimester ofpregnancy; therefore it is understandable that the
number of abortions significantly increased incontinental Europe and the British Isles comparedto the spring quarterly report.
Equine herpesvirus myeloencephalopathy also
follows a seasonal pattern with the majorityof outbreaks occurring in the first, second andfourth quarters in the Northern Hemisphere.
Localized outbreaks were reported from acrossthe USA and Canada. Single outbreaks werereported from Scandinavia and the British Isles,
and two outbreaks were reported from central
Europe. A few scattered equine infectious anemia
cases were reported in the USA and Canada. A
single report was received from France.
Year-round vector activity occurs in regions
bordering the Gulf of Mexico. Four cases ofEastern equine encephalitis were reported in
Florida. Although early for the season and quarter,a single case of West Nile virus was identified
in the Midwest Region of the USA. During
the quarter, there were 35 positive samples forrotavirus A or B and close to 100 Rhodococcus equipositive samples reported. These numbers were
derived mostly from the Lexington, Kentucky,laboratories. While many samples were submitted
from within Kentucky, a significant number werefrom other states. Nine cases of rotavirus and
11 of Rhodococcus were reported from France.
Miscellaneous: Contagious equine metritis:Three reports of Taylorella equigenitalis(the cause of CEM) were reported from
Germany. It is currently unknown whether
these cases were epidemiologically connected.
Lutz Goehring
University of Kentucky Gluck equine researchCenter - Department of Veterinary Science.
l.goehring@uky.edu

The Ridden Horse Checklist
The Ridden Horse Pain Ethogram (RHpE), otherwise known as the ridden horse checklist, was developed as a tool to facilitate recognition of lameness. There is evidence from Denmark, Sweden,
Switzerland and the United Kingdom that at least
50% of the sports and leisure horse populations
that are considered by their riders to be working
comfortably are actually lame, indicating that riders and trainers are poor at recognizing lameness.
Horses are stoical and generally compliant, despite experiencing discomfort. As prey animals,
horses have developed adaptations of movement
to mask pain. They reduce the range of motionof the thoracolumbosacral region, shorten step
length, reduce the height of arc of foot flightand increase duty factor (the proportion of thestride time that a limb bears weight), all to spreadload among limbs. These adaptations can leadto muscle atrophy, altered neuromuscular pathways and sometimes the development of othersecondary problems, which can make successful treatment and rehabilitation more challenging than if lameness had been recognized earlier.
There are many myths in the equestrian worldthat have been perpetuated through generations.
It has been accepted that there are grumpy, difficult, ‘stressy’ or lazy horses. Abnormalities ofcanter (for example, close temporal and spatial
placement of the hindlimbs, so-called bunny hopping) have been regarded as training problems.
People say, ‘My horse hates dressage but hejumps well, so there cannot be anything wrong,”
without asking why the horse struggles to work
well on the flat. As a result, the horse or the rider
get blamed by trainers without anyone questioning why a horse is unwilling or shows tension.
Coercive training methods are sometimes adopted(‘use a longer whip’ or ‘use a stronger bit’), with thepotential for any underlying problems to worsen.
The RHpE was developed as a tool to facilitate therecognition of pain-related poor performance andpain-induced gait abnormalities. An ethogram isa series of behaviors, each with strict definitions(for example, mouth opening with separation of
the teeth for 10 seconds or more). By comparisonof extensive video footage of non-lame and lamehorses acquired during ridden work, an ethogram
comprising 117 behaviors was developed.
Through application of this ethogram to non-lameand lame horses,

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

JULY 2023 | 3

I NT E R N AT IO N A L
24 behaviors were identified (for example, ears
pinned back for 5 seconds or more and repeated
tail swishing), the majority of which were atleast 10 times more likely to be seen in a lamehorse compared with a non-lame horse. These 24
behaviors comprise the RHpE and, by comparing
non-lame and lame horses, it was shown that thedisplay of eight or more of the 24 behaviors is
likely to reflect the presence of musculoskeletal
pain. However, some lame horses have a
RHpE score less than eight and any of the 24
behaviors could be caused by a variety of factors.
Therefore, it is the total score which is important.
The RHpE was applied to ridden horses
before and after resolution of lameness using
diagnostic anaesthesia (nerve blocks). There
was an immediate and substantial reductionin the RHpE scores, demonstrating a causal
relationship between the behaviors and pain.
This also indicated that the behaviors were nothabitual but were a direct response to pain. It
has been demonstrated that the RHpE can beused by non-trained individuals from a variety
of professional backgrounds to differentiate
between lame and non-lame horses, althoughtraining improves the accuracy of its application.
The RHpE was applied to 40 horses when riddenby the normal rider and a single professional rider,performing a purpose-designed dressage type
test. Overall, the gait quality was improved when
the horses were ridden by the professional rider;however, the total RHpE scores were similar,
although some of the individual behaviors thatwere displayed differed. This means that a horsewith musculoskeletal pain may appear to movebetter when ridden by a skilled professional
rider than when ridden by the normal rider, butbehavioural signs of pain cannot be masked.
The RHpE has the potential to be used in manydifferent circumstances. It can be used as amonitoring tool to facilitate early recognitionof musculoskeletal pain, to differentiate a painrelated or training-related problem, to help
determine if a saddle fits a horse or causes
discomfort, for a trainer to advise a client that
their horse probably has a problem and to assess
the likely presence of discomfort in a horse which
is being tried prior to purchase. Additionally, aveterinarian can use the RHpE as a tool to assess
whether nerve blocks have fully resolved pain
causing poor performance.

4 | EQUINE DISEASE QUARTERLYThe RHpE has been applied to horses warming
up for dressage at five-star three-day events, andduring the dressage tests at low-level eventing andvarious levels of Grand Prix dressage. At all levels,
the majority of horses had a low RHpE score (twoor three/24 at upper-level competitions; four tosix/24 at lower-level competitions), which supports
the social licence to ride horses in competitions.
However, a minority of horses had higher scoresand high scores have been associated with poorer
performance at all levels and in all disciplines.
At five-star three-day events, horses that scoredseven or more compared with horses whichscored less than seven had higher dressage
penalties, were more than twice as likely to beeliminated or retire cross-country, and thosethat completed had lower final places. It istherefore suggested that investigation of horses
with higher scores, followed by appropriate
treatment and management, has the potential to
improve both equine welfare and performance.
The RHpE is a valuable, scientifically-validated
tool for assessment of pain in ridden horses.
S u e D y s o n , M A , Ve t M B , P h D , F R C V S
sue.dyson@aol.com

NATIONAL
Unsanctioned Racing’s Role in Equine
Infectious Anemia (EIA) and Equine
Piroplasmosis (EP) in the United States

Unsanctioned, commonly called “bushtrack”,
racing has occurred in certain regions of theUnited States for decades, however, it has only
been recently that state and federal animal healthofficials identified the connection of this activity
to widespread transmission of equine blood-borne
diseases. Outbreaks of equine piroplasmosis (EP,Babesia caballi, Theileria equi) in clusters ofQuarter Horse racehorses in Florida in 2008 andMissouri in 2009 were the first instances where
involvement in bushtrack racing and iatrogenictransmission were key factors in the disease
spread. Increasing numbers of equine infectious
anemia (EIA) cases began to be confirmed in
Quarter Horse racehorses around 2013 and now
are the predominantly affected breed/discipline
in annual U.S. EIA cases. There is frequentcross-over of Quarter Horse racehorses between
sanctioned and unsanctioned race events,

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

N AT IO N A L
so EIA and EP testing requirements toenter
sanctioned
racetracks
providesthe primary mechanism by which newdisease
cases
are
being
identified.
From 2008 through 2022, a total of 541 casesof EP and 409 cases of EIA were confirmed incurrent or former Quarter Horse racehorses,
many of which had ties to unsanctioned racing.
Iatrogenic transmission via unhygienic practices
was identified as the cause of spread in all casesand some horses were found dually infected withboth EIA and EP. The most common methodsof transmission included the reuse of needles/
syringes/intravenous administration sets between
blood contamination of multi-dose drug vials,
administration of illegally imported blood andplasma products from other countries and direct
blood transfusion between horses for the purposeof increasing athletic performance (blood doping).
The EIA cases in this population have highlighted
a significant shift in epidemiology of EIA in
the U.S. While EIA cases used to be primarily
identified in untested or undertested herds withnatural fly-bite transmission as the cause of
spread, since 2017, the majority of EIA cases
annually are now in Quarter Horse racehorses
with iatrogenic transmission identified as thecause of spread. In 2022, 96 cases of EIA wereconfirmed in 16 states and 84 of the cases werein Quarter Horse racehorses with iatrogenictransmission either suspected or confirmed.
Given that iatrogenic transmission is a humancaused event easily prevented by good hygieneand biosecurity, these are cases of disease
spread which could have been prevented.
Additionally, some of these clusters of cases havean identified source of horses illegally moved
into the U.S. from Mexico, where both EIA
and EP are endemic and have high prevalence.
Recent investigation of bushtrack racing bystate and federal animal health officials has
identified at least 121 bushtrack located in 28
states, although many more have yet to be found.
Increasing numbers of bushtrack venues andhigher participation levels have been fueled inrecentyears through social media platforms.
These platforms have become the main method bywhich bushtrack event organizers and participants
communicate race dates, advertise match ups andacquire new fans and spectators. While mostbushtrack races draw several hundred spectators
each race day, some high-volume venues
routinely support several thousand spectators.

Since no rules are in place for horse or rider safety,
many welfare issues are commonly encountered.
Participating horses are maintained on
performance enhancing drugs and all horses
are medicated on race day, with some given
narcotics immediately before the race. Horses are
raced lame, racing surfaces are poor, whips areused excessively, electronic shock devices are
employed and catastrophic breakdowns during
the race are common. Most races are recorded
on video and posted to social media platforms,
so evidence of these welfare issues is readily
available. Many other illegal activities have been
documented at these venues beyond illegal racing
and gambling, so coordination across multiple
state and federal authorities would need to be
employed to address the situation with any effect.
Bushtrack racing at the current level ofoccurrence has significant negative impacts on
sanctioned horseracing. As previously noted,
frequent cross-over of horses between bushtrack
and sanctioned races has been documented andexposes sanctioned horses and racetracks topotential EP and EIA transmission. Additionally,
rampant drug use in bushtrack horses causes
long-term damage to horse health and impacts
future breeding performance for stallions
and mares recovered from bushtrack circuits.
Further, welfare issues observed at bushtrack
and seen in internet-posted race videos
are perceived by the general public as
occurring in all horseracing, resulting ina negative stigma on sanctioned racing.
From an animal health and infectious disease
perspective, veterinarians play a critical rolein identifying horses that may be participatingin bushtrack activities and providing disease,hygiene and biosecurity recommendations tohorse owners to prevent EIA or EP infection.
Unfortunately, bushtrack participants rarely use alicensed veterinarian, so opportunities to educate
or test horses may be sparse. As a result, the best
opportunity to test horses leaving this populationis during veterinary prepurchase examinations forclients converting these horses to a new athletic
focus after racing. Equine practitioners should
routinely test current or former Quarter Horse
racehorses for both EP and EIA to prevent spreadof these diseases into other equine populations.
Angela Pelzel-McCluskey
DVM, MS USDA-APHIS
Veterinary Services Fort Collins, Colorado
Angela.M.Pelzel-McCluskey@usda.gov

JULY 2023 | 5

KENTUCKY
Gastroduodenal ulceration syndrome
in foals in central Kentucky from 20202022

Gastroduodenal ulceration syndrome (GDUS) in
foals is a recognized but poorly understood disease
syndrome in which foals may display decreased
growth, colic, bruxism or no apparent clinicalabnormalities. Ulceration of the stomach can be
confirmed via gastroscopy and, in a subset ofcases pyloric, duodenal stenosis can be identified.
This then leads to decreased gastric emptying
and may result in gastric reflux or rupture.
Once stenosis occurs, medical management isoften unsuccessful and surgical intervention
may be required. Surgical intervention carries asignificant financial investment and studies reportvariable prognosis for long term survival. Medical
management may include supportive care, antiulcer medications and treatment of any inciting
disease, such as enteritis.
A portion of foals with GDUS will perforate thestomach or duodenal resulting in septic peritonitis
and death. Foals which died or were euthanized
due to gastroduodenal ulceration syndrome
and submitted to the University of Kentucky
Veterinary Diagnostic Laboratory had additional
samples collected for testing with specificemphasis on the presence of common infectious
agents that cause diarrhea in horses.
From 2020 to 2022, 16 foals with gastricduodenal ulceration syndrome were submitted
for necropsy and further testing. Ages ranged
from 3 weeks to 5 months (average of 63 days)
with 14 Thoroughbreds, one Warmblood and
one unspecific breed. In all cases, aerobic andanerobic culture of the large and small intestine,
as well as PCR for equine coronavirus, equine
rotavirus A, Lawsonia intracellularis, Salmonella,
Clostridium perfringens and Clostridioides
difficile was performed. The pH of gastric andduodenal fluid was measured in 15 of 16 cases
and a fecal flotation for parasites performed in 14
of16 cases. Equine Rotavirus A was detected in 8
of 16 cases; Salmonella sp. in one of 16 cases; andC. difficile in two of 16 cases. Gastric pH ranged
from 3.22 to 6.87 (average of 5.2) and duodenal
pH from 4.49 to 8.1 (average of 6.29). Visuallyapparent lesions were evident in the stomach in allcases, with ulceration (16 of 16) and perforation(nine of 16) most commonly observed.

6 | EQUINE DISEASE QUARTERLY

Findings within the proximal duodenum andjejunum included enteritis (10 of 16), ulceration(three of 16) and perforation of the duodenum(three of 16). Microscopic findings included severe
hyperkeratosis and necro-ulcerative gastritis of
the non-glandular stomach, necrosis, ulcerationand fibrosis of duodenum and inflammation of theoutside of the intestines in cases of perforation.
Additional findings included hepatitis (six of16) and pancreatitis in (five of 16). Interestingly,
findings from this group highlight the presence ofrotavirus A in 50% of foals with gastroduodenal
ulceration syndrome as well as the presence ofconcurrent hepatitis and pancreatitis in 31% ofcases. Inflammation of the intestine, liver andpancreas is similar to the syndrome referred to as
triaditis, which is recognized in small companion
animals. This extension of infection andinflammation outside of the stomach and intestine
may contribute to morbidity and mortality in thesecases and may have diagnostic significance if
correlations between hepatic values or pancreatic
enzyme levels and GDUS can be identified. The
significance of the high rate of PCR positivity
for equine rotavirus A is not well understood andwarrants further investigation.
Importantly, the primary cause of gastriculceration, hyperkeratosis and gastritis in thesecases is still unknown. Possibilities include
stress, dietary changes, abnormal gastric pH
secondary to motility abnormalities and vascularcompromise. While an in-depth epidemiologic
evaluation would be required to identify risk
factors contributing to this condition, theseoverall findings provide some interesting insight
into a common condition in foals.
Rebecca Ruby
BVSc, DACVP, DACVIM-LAIM
University of Kentucky Veterinary Diagnostic
Laboratory
Lexington, KY
Rebecca.ruby@uky.edu