APRIL 2024 VOLUME 33, NO.2

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

Growing Equine ‘Mini-Guts’ toInvestigate Infectious Causes ofIntestinal Illness in the HorseFirst Quarter 2024..............P. 3
NATIONAL

Vesicular Stomatitis Returns
with a New Bag of Tricks..P. 4
KENTUCKY

The 2022 Kentucky Equine
Survey: Measuring a
Decade of Change......... P. 5,6
KENTUCKY

Insulin Dysregulation (ID)and the Link to Laminitis:“Why Diagnostic Testingis Important”...............P. 6,7,8
T H ANK YOU S PON SO RS!

Gastrointestinal disorders represent a range ofserious, potentially life-threatening conditions
that continue to be a major challenge to horseowners and the equine industry, leading tosignificant financial costs associated withprevention and treatment as well as the loss ofhorses of all ages. A major roadblock in studying
and understanding disease outcomes associatedwith infectious causes of colic is a lack of relevant
laboratory model systems in which to model
intestinal infections. To overcome this obstacle,
the Shaffer Laboratory developed microscopic,
organ-like systems (termed ‘organoids’) froma variety of horse tissues to study bacterial andviral equine infectious diseases. Importantly,
due to their unlimited self-renewal and tissue
expansion, organoids bridge the gap between
the laboratory and disease models, providing an
attractive alternative to animal experimentation.
In addition, organoids have emerged as aninvaluable tool for accurately predicting drug
metabolism and response, such that they
represent an ideal platform for therapeutic
discovery and pre-clinical development.
When generated from the intestines, minigut organoids (referred to as ‘enteroids’)
reproduce the unique characteristics andmicroarchitecture of the equine gastrointestinal
tract, providing a robust laboratory model tomimic the horse intestine. While enteroids
grown in a three-dimensional (3D) configuration
are beneficial for long-term culture andfunctional
characterization,
host-pathogen
interactions are more challenging to model.
For example, enteroids grow in a wide rangeof shapes and sizes, leading to inconsistent
approximation of equine cell numbers andinaccurate or unpredictable bacteria-to-cellratios. Moreover, pathogens invade tissues
using receptors localized to the luminal host cellsurface. Unfortunately, ensuring that bacteria orviruses gain access to the enteroid interior where
luminal cell receptors are located is technicallychallenging, time-consuming and difficult tostandardize. To address this challenge, our lab
developed methods to manipulate enteroids toallow bacteria or viruses access to critical cell
receptors. Our first approach involves imbedding
parts of enteroids onto a semipermeable
membrane submerged into specialized media
that encourages normal cell division andarchitecture. In this system, enteroids selfassemble such that the luminal cell surfaces(those that would normally be on the inside of theintestine) are exposed and accessible from the
top of the culture dish. This technique provides
a more convenient, consistent and precise
way to control equine cell numbers and allows
us to easily infect enteroid-derived tissues.
Our second method involves attaching enteroid
tissue onto microfluidic chip devices capable ofdirectional fluid flow and mechanical deformationthat applies physical stretch across the chip.
Critically, these normal, physiologic forces
generate a tissue microenvironment that moreaccurately mimics the directional flow of digesta
traveling through the gut via wavelike peristalsis.
These chips developed in our lab consist of twoparallel channels separated by a semipermeable
membrane that enables “cross-talk” between theinterfaced gut tissue and an artificial vasculature
created by an equine endothelial cell barrier.

APRIL 2024 | 1

Therefore, these gut-on-a-chip models recreate amulti-tissue system similar to blood vessel linedorgans in a living horse. Notably, this systemaffords the opportunity to study the frontline
defense to infectious agents; introduction of
immune cells through the endothelial channel
allows us to monitor pathogen-induced cellularmigration from the artificial vasculature into thegut tissue. In this configuration, immune cells exit
the vasculature channel to neutralize invading
pathogens in the gut tissue channel, thereby
replicating host defenses elicited during infectionin the horse.
Using advanced laboratory techniques, wevalidated and demonstrated the functionality of
our enteroids. For example, we determined that,similar to tissues within the horse gastrointestinal
intestinal tract, equine enteroids exhibit barrier
functions, relevant brush border enzyme
activities and mucus production. Further, we
compared cellular differentiation patterns within
enteroid systems using immunohistochemistry
and advanced RNA sequencing analyses. Acrossour various techniques, we determined that ourpolarized enteroid model exhibits increased
cellular differentiation compared to 3D enteroids.
However, the addition of biomechanicalforces (stretch and flow) in the gut-on-a-chipsystem demonstrated the highest level of cell
type variation, reinforcing our hypothesis thatmicrofluidic devices generate the most life-likelaboratory environment in which to study equine
infectious disease outcomes.
Our aim is to develop versatile enteroid models
for both bacterial and viral infections. Since
Salmonella is one of the most common causes ofbacterial enteritis in the horse, we first used ourenteroid platform to evaluate the effects of bacterial
infection on host inflammatory responses. In
initial studies, we analyzed how S. Typhimurium
uses bacterial nanomachines to inject virulenceproteins into intestinal cells to manipulate hostimmunity and enable colonization. Building on
our success, we are using our unique models
to investigate additional aspects of microbial
pathogenesis and to accelerate the developmentof novel vaccines to combat infectious disease
threats to the equine industry. For example, equine
rotavirus B has emerged as a significant healthand economic concern and continues to cause foal
diarrhea outbreaks in Kentucky and other states
including New York and Pennsylvania.

2 | EQUINE DISEASE QUARTERLY

We are the first laboratory to demonstrate
productive equine rotavirus replication in
our intestinal enteroid cultures – a criticalexperimental step that will enable future vaccine
development.
Overall, our organoid technologies can be used tounderstand how pathogens interact with specificequine tissues, to explore new ways to prevent
infection and to discover effective drugs to combat
infectious disease. Furthermore, developing
additional equine organoid models will provide
the experimental foundation for numerous
studies focused on tissue injury and regeneration,
inflammation and infection control, pre-clinicalanalysis of new therapeutics, toxicology anddrug metabolism studies and the identification ofgenetic factors that determine disease outcomein the horse. Our organoid-to-microfluidic chippipeline is rapidly pioneering the way towards
successful equine precision medicine that willallow us to develop effective medical intervention
strategies in the lab. Ultimately, our platform will
reduce animal experimentation and is accelerating
progress in disease modeling, vaccine design anddevelopment, understanding infectious disease
outcomes and investigating regenerative medicine
in the context of the dynamic physiology of thehorse.

Lynn M. Leedhanachoke, MS, DVM
Department of Veterinary Science
108 Gluck Equine Research Center
Lexington, KY 40546
lmle224@uky.edu
Carrie L. Shaffer, PhD
Department of Veterinary Science
108 Gluck Equine Research Center
Lexington, KY 40546
carrie.shaffer@uky.edu
Phone: +1(859) 218-1168

Please visit our Gluck Website:

EQUINE DISEASEQUARTERLYEDITORS
Lynne Cassone
Lutz Goehring
Allen Page
STAFF
Holly Wiemers
Hendri Smeenk

I N TE R N ATIO N A L
First Quarter 2024

International report on equine infectious
diseases.
This report collates information provided bydiagnostic laboratories in Lexington, Kentucky,
University of Kentucky Veterinary Diagnostic
Laboratory (UKVDL) and Equine Diagnostic
Solutions, Inc. (EDS). We want to thank IDEXX
laboratories providing data for Germany.
We have further included information fromthe International Thoroughbred Breeders
Federation, the International Collating Centre(ICC) in Newmarket/Cambridge, United
Kingdom, and information from the American
Association of Equine Practitioners’ Equine
Disease Communication Center (EDCC). This
report summarizes heightened activity of several
relevant contagious or environment-linked
diseases among equids. We encourage everyone
to report laboratory-confirmed (toxico)infectious
disease of Equidae to the ICC in Cambridge, UK,
or EDCC, USA. With few exceptions, reports arefrom Europe and North America.
Information from all our sources shows Strep.
equi spp. equi (Strangles) as the most frequently
and consistently diagnosed equine pathogen for
the first quarter of 2024. Reports from various
sources reflect ‘newly diagnosed’ infection.
There have been sporadic reports of equine
influenza virus, both from Europe and North
America.

Two equine Rabies cases were reported from theEastern United States, and single cases of EIA
throughout North America. In Europe, EIA wasdiagnosed in Belgium, Germany and Hungary.
A case of Glanders (Burkholderia mallei) was
reported from Iran.
Many mares are in or entering their third trimesterof pregnancies. Not surprisingly, the numbers for
EHV-1 (and EHV-4) abortions are up for the firstquarter. All reports of EHV abortion originate
from Europe, while there are no reports from
North America. However, this is likely becauseof underreporting as UKVDL reports five fetuses
aborted due to EHV-1 for the last quarter. Theirdata shows abortions in various breeds.
For the first quarter of 2024 there has been adrastic increase in EHV-1 neurologic disease(EHM) cases/outbreaks, both in North America,
more than 20, and (primarily) Northern Europe(about 15). Our German sources, on the other
hand, are reporting very low EHM activity for the
first quarter. Affected breeds were Thoroughbred,Standardbred, Warmblood, Draft horse, Quarter
Horse and “Pony.” While EHM outbreaks areoften associated with “traveling horses,” there
were a number of reports without this association,suggesting spontaneous and differently triggered
reactivation from latent carriers.

Lutz Goehring
Edward O. Olajide
Gluck Equine Research Center –Department of Veterinary Science University of Kentuckyl.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

APRIL 2024 | 3

N AT IO N A L
Vesicular Stomatitis Returns with a impacted California, a state which had never
New Bag of Tricks
previously recorded a natural incursion of the
If there’s one thing we’re learning about climatechange’s effects on vector-borne diseases, it’s thatthe diseases will do something different and we
can’t predict quite what that is going to be. Whenvesicular stomatitis reappeared in the UnitedStates in 2023 after a three-year hiatus, the factthat a new incursion occurred was not a surprise;rather, everything else about the outbreak wasout of character, from the geographic locations
affected, to the species of animals that developed
lesions, to the natural disasters that altered the
trajectory of disease occurrence.

Vesicular stomatitis virus (VSV), spread byblack flies, sand flies and biting midges, causes
blister-like lesions on the muzzle, tongue andcoronary bands of affected livestock. The virus
circulates year-round in southern Mexico andonly occasionally moves into the U.S. whenclimate factors support expansion of the infected
vectors northward. Equids are most commonly
infected, but cattle cases also occur. While otherlivestock species are susceptible, such as llamas,
alpacas, pigs, sheep and goats, only a handful ofcases in those species are diagnosed. The painful
lesions heal on their own in a couple of weeks
and most affected animals only need supportive
care, but the trade ramifications and movement
restrictions for livestock during an outbreak
are significant. International movement ofsusceptible livestock may be halted from affectedstates, and even states without cases may haveto test animals prior to export. Shows, eventsand county fairs may be canceled, and nonaffected states restrict movement of livestockfrom affected states. The outbreak usually lasts
for months through the vector season (summer
to fall), and often continues into winter as
vectors die off or go dormant. Meanwhile,horse owners struggle to meet requirements tomove to their shows and events and, as cases
spread, they may suddenly find themselves ina newly-affected area and cannot return home.
Simultaneously, they’re frantically applying fly
spray to horses and implementing aggressive fly
mitigation strategies on farms to prevent theiranimals from contracting the disease. Vesicularstomatitis virus is zoonotic, so humans can get
infected from handling livestock with lesions,(yet another flu-like illness to worry about!)
The 2023 VSV outbreak that produced 319
infected premises (311 had infected equids),
ran from May 17, 2023, to Jan. 18, 2024, andprimarily

4 | EQUINE DISEASE QUARTERLY

disease from Mexico. For decades, Southern
California had been protected from incursions
by extreme drought conditions, but the Winter of2022 saw heavy snow and Spring of 2023 brought
buckets of rain. Lush vegetation abounded; theflies and midges thrived and expanded theirrange over the border carrying the virus. The only
previously recorded VSV cases in California werecaused by human error, not a natural incursion,and occurred in the 1982-83 outbreak when
infected dairy cattle were moved from Colorado.
As the case counts increased quickly in horses
in Southern California in Summer 2023, anothernew development occurred when a wildlife parkin the region discovered multiple VSV-lesioned
rhinoceros in their herd. Rhinos are a species that
had never been identified as susceptible, and,ultimately, all 26 of the park’s rhinos became
affected and struggled with lesion healing.
Some of the rhinos sloughed their foot pads andbecame badly lame, in addition to not wanting
to eat or drink with sloughing tongue mucosa.
Rhinoceros share ancient genetic lineage withhorses, so perhaps we should have guessed theirsusceptibility.
Climate change wasn’t done surprising us as
Hurricane Hillary formed in August and tookshockingly rare aim at Southern California. The
resulting flooding seemed to flush the vector eggs
and larvae out to the Pacific, which stopped theoutbreak in Southern California. Cases continued,
however, to move northward from the Central
Valley and eventually as far as Sacramento
County before the cold snaps in early January2024 finally ended the outbreak. VSV incursion
years are often followed by overwintering of thevirus, and expansion year outbreaks, so it remains
to be seen if this will occur in such a novel
outbreak region like California. As a previously
drought-riddled region becomes verdant (anew lake has formed in Death Valley!), climatechange continues to keep us guessing about
what new tricks an old vector-borne disease canperform. A multi-disciplinary research teamincluding USDA, state, laboratory and university
collaborators has begun studying the impacts ofclimate parameters on VSV occurrence hoping tobetter predict what the virus has in store for us in
the future.
Angela Pelzel-McCluskey, DVM, MS
Angela.M.Pelzel-McCluskey@usda.gov
USDA-APHIS-Veterinary Services
Fort Collins, Colorado

K E N T U C KY
definitionencompasses
placesThe 2022 Kentucky Equine Survey: This
includingcommercial
breeding
andMeasuring a Decade of Change
training
facilities,
competition
facilities,
In any business or industry, good records
help decision makers make good decisions.
However, in general, the equine industry is one
where market data is scarce. Industry-specificstudies are not inexpensive, but they are worth
the investment. A decade ago, the University of
Kentucky and the Kentucky Horse Council joined
forces to conduct the 2012 Kentucky Equine
Survey, a comprehensive, statewide surveyof horses, ponies, donkeys and mules. Fastforward 10 years: UK and KHC teamed up again
to produce the 2022 Kentucky Equine Survey(KyES), allowing us to learn how the industry was
impacted by events of the past decade, including
emerging from the most significant contraction
since the Great Depression and World War II,
economic uncertainty following the COVID-19
pandemic and the highest inflation levels seen
since 1980. The information generated by thesestudies is intended to be a resource for a broad
set of decision makers, including policymakers,
elected officials, entrepreneurs and businessowners, researchers, educators, and veterinarians.

Statewide and national equine-specific studies
are essential because, due to the diverse natureof equine enterprises, traditional agricultural
surveys miss significant parts of the industry. The
United States Department of Agriculture (USDA)
Census of Agriculture, conducted every five
years, measures equine production on “farms,”
defined as any establishment that has at least$1,000 in cash receipts on the sale of agricultural
products annually or at least five equids. Thisdefinition largely excludes places that do not
engage in the production of horses, ponies, mules
or donkeys (breeding and/or selling). As a result,
we believe that Census of Agriculture estimates
undercount equids in Kentucky by more than 50%.
The purpose of the 2022 KyES was to determine
inventory estimates of Kentucky’s equine
operations and equids, and to measure economic
activity on equine operations. Data collection
was conducted by the Kentucky Field Office of
the National Agricultural Statistics Service, anagency of the USDA. The unit of observation wasan “equine operation” (as opposed to a “farm”),
which was defined as an address at which at least
one equid (horse, pony, mule or donkey) resided.

lessonbarns
andboarding
facilities,
nonprofit operations and personal residences.
Surveys were distributed by mail to 15,000
equine operations in Kentucky. Of those, 8,337
were returned with usable data (56% responserate). Results from the survey indicate that there
were approximately 31,000 equine operationsin Kentucky. Farms or ranches comprise thelargest type of equine operation (18,000),
followed by personal residences (10,000);boarding, training or riding facilities (1,000);and breeding operations (600). Another 1,400
operations indicated other primary functions.
There were an estimated 209,500 horses,
ponies, mules and donkeys in the state on July
1, 2022, which is down more than 13% from2012. Thoroughbreds (48,500) were the mostprevalent breed, followed by Quarter Horses(35,000), Walking Horses (28,500), Donkeys
and Mules (13,500) and Saddlebreds (12,000).
Most equids in Kentucky are used for trail andpleasure riding (62,500), followed by breeding(33,500 broodmares; 22,000 “growing” horses;
and 4,000 breeding stallions) and 32,500 equids
are idle, retired or otherwise not working. Morethan 45% of Kentucky’s equids are between
5 and 15 years old, with nearly one-quarter(24.8%) over 15 years old; about 20% 1 to 4
years old; and about 10% foals and weanlings.
The value of all equids in Kentucky was $6.5
billion. The total value of all assets, including
equine and equine-related assets (such as
land and buildings, vehicles and equipment
and so on), was estimated at $27.7 billion.
In 2021, income from sales of equids wasnearly $1.1 billion, while income from equinerelated services was $990 million ($450 million
from breeding services and $540 million fromnon-breeding services). Accordingly, totalequine-related income from sales and services
was almost $2.1 billion 2021. In the sametime frame, total equine-related expenditures
amounted to $1.6 billion ($535 million in capital
expenditures and $1.03 billion in operating
expenditures, excluding labor). Of these
operating expenses, 82% were spent in Kentucky.

APRIL 2024 | 5

K E N T U C KY
Kentucky’s equine operations employed 12,500
workers (6,300 full-time and 6,200 part-time
employees), with total payroll expenses of $322
million and non-wage benefits of $30 million.
Labor expenses were highest for breedingrelated activities (35%), followed by racing(13%), recreation (11%) and competition (9%).
Equine owners were asked to identify whichequine health issues are most important. The
top three equine health concerns were caring forsenior equine (27.1%), musculoskeletal issues(22.4%) and digestive problems (17.4%).
Comparing the results from the last two surveys
suggests some strengths: an increase in thevalue of equids sold; equine operation income
increased more than expenses; and a smaller
supply of equids, coupled with a decline in nonpaid transfers, suggests that the risk of horses
becoming unwanted has lessened.
The decline in the number of equids and equine
operations in Kentucky is being experienced by
all facets of animal agriculture across the nation,
providing research opportunities to explore thedriving factors of these declines within the entire
agricultural industry.
Understanding the number and location of equids
is critical to ensuring the health of these animals
and the future sustainability of the industry. This
information drives provision of veterinary andother business services, research programs andeducational outreach. For Kentucky, the 2022
KyES reinforces the economic significance ofequine agriculture, which remains vibrant andstrong as a signature industry in Kentucky,
generating investment, tourism, recreation andpositive symbolism for the state.
The full report and supplementary materials(detailed methodology, county fact sheets andadditional detailed state- and county-level
analyses) are available online athttps://equine.ca.uky.edu/kyequinesurvey.
C. Jill Stowe
Professor
Department of Agricultural Economics
jill.stowe@uky.edu

6 | EQUINE DISEASE QUARTERLY

Insulin Dysregulation (ID) and the
Link to Laminitis: Why Diagnostic
Testing is Important
Over the past two decades, research has improved
our understanding of the most common equine
endocrine diseases: pituitary pars intermedia
dysfunction (PPID, formerly referred to as
Equine Cushing’s disease), and equine metabolic
syndrome (EMS). One of the most critical new
findings is that insulin dysregulation (ID) is the
key driver of horses developing endocrinopathic
laminitis, or now called hyperinsulinemiaassociated laminitis (HAL), formerly referred to as
founder. As we learn new information about these
disorders, we continue to change the guidelines
and recommendations for diagnostic testing. If ahorse is suspected to have one of these endocrine
disorders, timely and accurate diagnostic testingis key for developing a management and dietaryplan to lower the risk of these horses developing
laminitis. Diagnostic testing and outcomes are
not a “one-size-fits-all” model, as there aredifferent metabolic types. Thus, evaluating thecomplete picture, including both clinical signsof disease and diagnostic testing, is critical.

Brief Review of PPID, EMS and the
involvement of ID

ID is the key feature and top concern for equids
with EMS, and ID can coexist in equids with
PPID. PPID is a progressive and debilitating
disease affecting older horses of all breeds witha reported prevalence of more than 20% in horses
older than 15 years and more than 25% in horses
older than 20 years. PPID is characterized byabnormal growth and function of the pituitary
gland in the pars intermedia region, causing
abnormal secretion of various hormones.
This then contributes to the clinical signs seen
with PPID, which can be varied and include
hypertrichosis/hirsutism (overabundant hair
growth and failure to shed hair), weight loss,
abnormal fat redistribution, muscle wastage/
atrophy, lethargy and depression, polyuria/
polydipsia (increased drinking and urination)and increased susceptibility to infections such as
sinusitis and hoof abscesses being most common.

K E N T U C KY
Whilst most PPID cases can occur without EMS/
ID being present, PPID can coexist in a subset ofhorses with both EMS/ID. Horses with PPID andID will be at a higher risk for laminitis, but at thistime the specific link between PPID and ID has
not been fully clarified.
EMS is extremely common, with a recent study ofponies and cobs in the United Kingdom reportinga prevalence of 23%. The breeds most at risk ofdeveloping EMS include the pony breeds, Spanish
breeds, gaited breeds, Morgans, miniature horses
and warmbloods. These breeds have a highgenetic risk of developing EMS with only mild
environmental influences, although other horses
with lower genetic risk can still develop EMS if
pushed by environmental factors including dietand lack of exercise. Ultimately, EMS is not asingle disease but a collection of risk factors for
endocrinopathic laminitis - the leading cause oflaminitis. At the core of this group of risk factors
is ID and generalized or regional adiposity (cresty
neck and subcutaneous deposits of adipose tissue
behind the shoulders and at the tail head). Thatbeing said, we now know that not all obese
animals are ID. Indeed, some animals may havea lean phenotype and are considered the nonobese manifestation of EMS, while these are often
horses with PPID and EMS.

ID is characterized by an abnormal, postprandial(after feeding) metabolic response, especiallywith diets containing increased levels ofcarbohydrates. It is this abnormal insulin responsethat increases the risk of horses developing HAL,a painful hoof condition which often results inthe need for euthanasia. While increased insulin
is concerning when sustained hyperinsulinemia
over ~100 uIU/mL is observed, precise cut-offs
are unknown at this time. Regardless, the key topreventing laminitis is the appropriate diagnosis
of ID and subsequent management changes tomaintain healthy postprandial responses to dietsby lowering circulating insulin responses.

How to diagnose ID?
One should incorporate diagnostic testing for ID
if an equid has history or clinical signs of EMS,
or if one suspects an equid to be PPID and ID. ID
diagnostic testing should be considered during awellness or pre-purchase exam, when considering
corticosteroid use, or as a tool to help guide decisions
with nutritional management and monitoringof an equid that has been diagnosed with ID.

APRIL 2024 | 7

K E N T U C KY
ID is defined as any combination of the following:basal (resting) hyperinsulinemia, postprandial
hyperinsulinemia (response to the oral sugar test
or consumed feeds) or tissue insulin resistance(IR). The most accepted and practical in-field
diagnostic tests for ID are measuring resting(basal) insulin and/or performing dynamic testing
using the oral sugar test (OST). Measuring restingor basal insulin requires collecting a single
blood sample from an equid in the fed state (hayor pasture, but not grain, which is explained
further below); either plasma or serum insulin
concentrations are then used to detect resting
hyperinsulinemia (HI). This approach is reallyused for convenience sampling or monitoring, as
it has a low sensitivity/high specificity, meaning it
can detect more severely affected equids but does
a poor job identifying mildly affected equids.
Unfortunately, resting insulin levels canbe normal in some ID animals, whichemphasizes the importance of dynamic
testing using the OST. Resting insulin isalso useful when assessing postprandial
responses to a horse’s current diet regimen ormonitoring responses to management changes.
The two currently recommended dynamic tests
for diagnosing ID are the OST and the insulin
tolerance test (ITT). The OST is preferredbecause the insulin response reflects the naturalsequence of events that mimic the response to ameal, including digestion, absorption, hormone
responses, secretion of insulin from the pancreas
and risk of HAL, versus the ITT which measures
hepatic and/or tissue insulin sensitivity. To
conduct the OST, it is currently recommended
that the equid undergo a three to six-hour fast,
followed by administering either a low dose (0.15
mL/kg) or high dose (0.45 mL/kg) of lite cornsyrup. Recent research characterizing the OST
test has indicated a few important considerations
when testing, including the fed vs fasted stateof the animal prior to the OST; low vs highdose of corn syrup; season; and stress. For more
information about these studies, contact Dr.
Amanda Adams (Amanda.adams@uky.edu).
Research has shown that winter and spring canexacerbate ID, thus one may avoid this time ofyear for testing or at least keep this in mind when
testing during these times. Currently there are
no seasonal reference ranges for diagnosing ID.

8 | EQUINE DISEASE QUARTERLY

In cases where ID is thought to coexist with PPID,
diagnostic testing for PPID is important. Today,
the most recommended and frequently useddiagnostic tests for PPID are 1) measuring baseline
plasma ACTH concentrations and/or 2) measuring
ACTH concentrations following the thyrotropinreleasing hormone (TRH) stimulation test, which
is believed to be the most discriminating method.
Determining which test is most appropriate for anindividual case should be guided by clinical signs
or stage of disease. If early stage is suspected, theTRH stimulation test is preferred. If moderate oradvanced PPID is suspected, assessing baseline
ACTH concentration may be sufficient. Retestingis recommended if results are not consistent withclinical signs. If results fall within equivocal
range, the TRH stim is recommended. Given thatseason has an impact on ACTH levels, if possible,
it’s best to avoid fall testing.
For all diagnostic testing purposes (PPID and/orID), it is critical to send samples to a reputablelab that has established reference ranges foreach of the tests. Since not all labs and assays
are the same, the same facility for sample
testing should be used, especially if comparing
results. Additionally, consider reviewing theEquine Endocrinology Group’s publishedguidelines for up-to-date diagnostic testing
protocols, and recommendations for reference
ranges and interpretation of testing results -https://equineendocrinologygroup.org/.

Additional information regarding the Adams’ Lab
research going on at the University of Kentucky’s
Aged Horse Research Center can be found atwww.seniorhorsehealth.com.

Dr. Amanda Adams
Associate Professor
Gluck Equine Research Center
University of Kentucky
Email: Amanda.adams@uky.edu
Phone: +1(859) 218-1168