Equine Disease Quarterly Newsletter

5

N AT I O N A L

Clostridial Myositis

C

lostridial myositis is a rare but serious bacterial infection, which causes inflammation anddeath of muscle and release of bacterial toxins into
the bloodstream. This condition is also referred
to as myonecrosis, malignant edema, and gas
gangrene. It occurs most often in horses that haverecently received an intramuscular injection. Clinical signs appear 6-72 hours following the injection,and horses initially exhibit acute swelling, heat, andpain of the affected area. The disease progresses
rapidly and the horse’s condition may decline
within hours. The affected animal exhibits signs ofsystemic toxemia; death can supervene rapidly insevere cases. Clostridial bacteria produce gas that
results in a characteristic emphysematous (bubbly) feel or crepitation of the region. Clostridial
myositis is a true medical emergency, with survival
linked to prompt intervention through aggressive
antibiotic treatment and wound debridement.
The Clostridium genus consists of over 150
known species of Gram-positive, anaerobic, sporeforming bacteria. The spore-forming ability ofthese bacteria allows survival for long periods oftime in the environment. When spores encounter alocation without oxygen, such as damaged muscle,
they are triggered to proliferate and produce exotoxins, which cause extensive tissue and vasculardamage. The clostridial species that commonly
cause myositis include C. perfringens, C. septicum
and C. chauvoei.
Clostridial myositis has been reported following
intramuscular inoculations of vaccines, ivermectin, antihistamines, phenylbutazone, vitamins,
prostaglandins, and most commonly, flunixin
meglumine. Infrequently, cases occur following
inadequate perivascular administration of compounds, foaling trauma, or puncture wounds. In a
study by Peek et al in 2003, stallions and Quarter
horses were overrepresented, and the authors hypothesized this might be due to the heavy musclingof these groups.
The mechanism by which the bacterial spores
arrive in the muscle of the horse is unknown.
It is possible spores are introduced at the time

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

JULY 2019
Volume 28, Number 3

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
First Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Changing Trends
in Equine
Reproduction  .  .  .  .  .  .  . 3National
Clostridial Myositis  .  . 5of injection. Another theory is that bacteria aretranslocated from their normal environment in
the intestine, in times of inflammation or colic
and arrive in the muscle via the bloodstream. No
association linking whether or not the injection site
is cleaned prior to injection and the developmentof myositis has been established. A higher incidence of myositis with irritating substances suchas nonsteroidal drugs and vitamins is reported,
potentially due to increased tissue damage andcreation of an oxygen-free environment.
Diagnosis involves aspirating a small amountof fluid for anaerobic culture and Gram-staining
to look for the presence of gram-positive rods. To
treat the infection, large incisions are made into themuscle and fascia to expose the bacteria to oxygenand debride dead tissue. General supportive careis critical because these bacteria produce toxinsthat have secondary effects on the horse, including the potential to reduce the contractility of theheart. Clostridial toxins may also result in anemia,
thrombocytopenia, and leukopenia. Horses arecommonly treated with high doses of intravenous
penicillin, intravenous fluids, cardiovascular sup-port, and wound care. Hyperbaric therapy, whereavailable, is suggested as an adjunct to routine
treatment.
Survival has been reported to range from 31%
to 73% and appears to be better for infections
with C. perfringens compared with C. septicum or
C. chauvoei. Horses that survive the initial toxemic
stages of disease have an improved prognosis. The
wounds created by a combination of infection andtreatment are usually large, and may take weeks
to months to heal entirely. Horses which do notsurvive show signs of intravascular coagulation andmulti-organ failure.
There is no definitive prevention for clostridial
myositis. When giving intramuscular injections,use large and well vascularized muscle groups, andwhen possible avoid giving irritating substances in
the muscle if there is an alternative route such asoral or intravenous administration.
CONTACT:
Rebecca Ruby, BVSc (dist), MSc, DACVP
Rebecca.Ruby@uky.edu(859) 257-8283
UK Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceIn an article contained in this issue of EDQ, Dr.
Troedsson nicely details advances in the scienceand practice of equine reproduction over the
past 50 years that have contributed to improved
fertility and breeding efficiency in the horse. It is
important to point out, however, that research conducted at the Kentucky Agricultural Experiment
Station at the University of Kentucky beginningover 100 years ago laid much of the groundworkfor understanding important diseases impacting
reproduction as well as the clinical evaluation ofstallions and mares for infertility. Beginning in
1911, Good and others worked to identify thecausative bacterium for outbreaks of infectious
abortion (Salmonella abortusequi). Subsequentdevelopment of a bacterin and control procedures
led to the eventual eradication of this importantcause of infectious abortions in the U.S. Research
by Dimock, later joined by Edwards and Bruner,
led to descriptions of techniques for the clinicalexamination of mares for pregnancy as well as adetailed description of clinical, bacteriologic andpathologic changes in the reproductive tract ofinfertile mares. This work provided the foundation
for recommendations related to breeding hygiene,
uterine infections, infertility as well as pregnancy
detection in mares. In 1933, research by this groupprovided early characterizations of equine (herpes)
virus abortion. They also conducted large studies
that characterized both infectious and noninfec-

tious causes of abortion in mares in Central Kentucky. Subsequent work by Doll, Bryans, and later
Allen in the Department of Animal Pathology at
UK lead to the development of the first live andinactivated virus vaccines for the control of equine
herpesvirus abortion in mares. In the mid-1950s,
Doll, Bryan, McCollum, and Crowe describedthe viral agent causing equine viral arteritis andabortion in mares with subsequent developmentof vaccination and control strategies based upon
the work of Timoney and McCollum in the mid1980s. Research by Loy and others led to a better
understanding of postpartum reproduction inmares, together with the use of artificial lighting
regimes and endocrine manipulation for control ofthe estrous cycle in mares. Although this chronology is incomplete and omits other significant research, I think that this historical perspective adds
to the work characterized in Dr. Troedsson’s article.
In particular, it demonstrates the need for researchexpertise and interest focused on reproduction in
the horse to address current problems as well as
unforeseen future problems related to equids.
CONTACT:
Barry A. Ball, D.V.M., Ph.D., D.A.C.T.
b.a.ball@uky.edu(859) 218-1141
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

2

3

4

I N T E R N AT I O N A L

First Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
For the period under view, African horse sickness (AHS) was reported by Cameroon, Chad, theRepublic of South Africa (RSA), and Swaziland.
Swaziland reported four outbreaks of AHS, eachinvolving very limited numbers of horses. Twooutbreaks of AHS were confirmed in Cameroon
and Chad. Both outbreaks in Cameroon involved
working horses and donkeys, and horses wereprimarily affected in Chad. Incidence of the disease was above average in the RSA, especially inGauteng Province. Sporadic cases were recordedin the remaining provinces in the AHS infected
area. No cases were reported to date in the Western
Cape Province, either in the infected or diseasefree areas.
Equine influenza (EI) was confirmed in numerous countries in Europe (Belgium, Denmark,France, Germany, Ireland, the Netherlands andthe UK), West Africa (Burkina Faso, Ghana, Mali,
Nigeria, Niger, and Senegal), and the USA. In
Europe, the outbreaks primarily involved unvaccinated horses, but the disease also was observedin vaccinated horses. Strains of clade 1, Florida
sub-lineage of H3N8 EI virus were implicated.
The major impact of EI in West Africa was seen in
donkeys, in which thousands of cases were reportedwith very high fatality rates. Equine influenza isendemic in the USA; 57 outbreaks were confirmed
in eight states during the first quarter of 2019.
Strangles remains endemic in most countries:
France (33 outbreaks), New Zealand (one outbreak), Sweden (three outbreaks), the UK (oneoutbreak), and the USA in which the disease isendemic. Eighty-four outbreaks were diagnosed in
18 states, with multiple outbreaks in three states.
Equine herpesvirus 1 (EHV-1) related diseases were reported by Belgium, Canada, France,
Germany, Japan, Norway, Sweden, the UK, andthe USA. The number of confirmed outbreaks ofrespiratory disease ranged from one (Norway andSweden), two (Belgium, the UK and the USA),and four (France). Cases of EHV-1 abortion
were diagnosed in Belgium (one), Canada (two),France (five), Germany (one), Japan (eight), Sweden (two), the UK (four), and the USA (eleven).

Equine herpesvirus 1 neurologic disease wasreported by France (three outbreaks), Germany(three outbreaks), Sweden (three outbreaks, eachinvolving multiple cases), and the USA (13 outbreaks in eight states, three involving multiple
cases).
Equine herpesvirus 4 respiratory disease wasrecorded in Argentina, Belgium, and the RSA (oneoutbreak apiece), Sweden and the UK (each withseven outbreaks), France (36 outbreaks), and theUSA, in which the disease is endemic.
Equine herpesvirus 2 infection was reportedby the USA, in some instances associated withrespiratory disease.
Bulgaria, Canada, Peru, and the USA confirmed
outbreaks of equine infectious anemia. The number of cases ranged from one (Bulgaria, Peru) to fivein Canada. The USA recorded the disease in fivestates, with the number of cases by state ranging
from one to nine.
Equine piroplasmosis was reported by Ireland(a case of Babesia caballi infection in an imported
mare and her aborted foal) and the RSA in which
the disease is endemic.
Cases of leptospiral abortion were confirmed
by Belgium (one) and the USA (two). The USA
diagnosed four cases of nocardioform placentitis,
three associated with Amycolatopsis spp and one
with Crossiella equi infection, and four other casesof mucoid placentitis.
Two cases of equine coital exanthema wereconfirmed in the USA.
Clostridial enterocolitis was diagnosed inneonatal foals in the USA, five of which wereassociated with Clostridium perfringens infection.
Additionally, four cases of C. difficile infection
were confirmed.
Of neurological diseases reported during thefirst quarter of 2019, one case of rabies and ninecases of Eastern equine encephalomyelitis werereported by the USA, all but one in Florida. During the same period, the RSA confirmed one caseof West Nile virus infection and 60 cases of equine
encephalosis that occurred in a total of five provinces. Mexico reported 41 outbreaks of Westernequine encephalomyelitis in the state of Nayarit.
Fifty-three cases of the disease were recorded inthese outbreaks, including seven fatalities.

Changing Trends in Equine Reproduction

R

esearch advances in equine reproductive biology and health over the past 50 years havecontributed to improved fertility and breeding
efficiency in horses. The development of endocrine
and ultrasonography diagnostics aids the clinician
in determining potential fertility of mares and stallions. Follicular dysfunction and ovulation failure
can be diagnosed with high precision in mares, embryo and fetal development can be monitored from10 days after ovulation throughout gestation, andfetal/placental abnormalities diagnosed to identify
high-risk pregnancies. In stallions, biochemicaland genetic sperm abnormalities have been identified that previously remained undetected basedon traditional breeding soundness examinations.
Furthermore, testicular abnormalities and bloodflow can be determined with high accuracy byDoppler flow ultrasonography.
The current trend in horse breeding is characterized by a decline in mares that are bred and a
new focus on wellbeing of established pregnancies
as well as enhanced genetic selection with regards
to health and future performance of the foal. In
addition, great advances in the area of assisted
reproductive technologies offer numerous possibilities that were not available in the past.
Monitoring Healthy Pregnancy

Biomarkers for high-risk pregnancies and efficient treatments to prevent late pregnancy losses
are being investigated. As new potential markers
for unhealthy conditions are discovered, effective treatment options need to be developed. A
similar trend is seen with regards to endometritis
as well as the development of new diagnostics fordormant bacteria and uterine biofilms. While
new therapeutic regimens for endometritis often
include non-antibiotic alternatives or supplements,
most treatment options for high-risk pregnant
mares include long-term use of broad-spectrum
systemic antibiotics without the possibility of
performing bacterial sensitivity tests. There is a
global awareness of consequences when antibiotics are overused in human as well as veterinary
medicine—and equine reproduction is not an
exception. An overuse of antibiotics can lead tobacterial resistance and contribute to one of themost urgent public health issues today. New trends
in equine reproduction reflect these challenges toAssisted Reproduction

Assisted reproduction is not suitable to all
breeders. However, current knowledge andexpected 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 andsubfertile stallions, allowing for treatment of thesemen. 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 withtiming 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 bycentrifugation of their ejaculates and re-suspensionof the sperm in an extender with supportive nutrients. Furthermore, the quality of an ejaculate
can be enhanced through gradient centrifugationthat can separate “good” and “bad” sperm before
insemination. Further research to enhance ourunderstanding of relevant sperm biology andadvanced diagnostics to identify preferable sperm
populations in an ejaculate is expected to create aneed for robust and efficient technologies to selectsuperior sperm within an ejaculate.
Research that makes it possible to separate
x- and y- bearing sperm through flow cytometry(based on the fact that x-bearing sperm contains
more DNA), has been commercialized and iscurrently offered by specialized laboratories. The
method is very accurate, but efficiency is still quite
low and results in a low number of sex-sorted
sperm. This hurdle has been a limiting factor
for the method and more research is needed to
improve the technique. Recent research exploring
the use of nanotechnology to target specific sperm
DNA sequences has the potential to develop a
new efficient technology to select sperm for sexsorting, and maybe more importantly—to selectveterinary medicine, public health and the global
equine breeding industry, and additional nonantibiotic treatment options need to be developed.
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 (bloodlines) and make breeding decisions based on theseevaluations. As equine breeding has shifted fromquantity to a greater focus on quality, genetics andgenomic research in reproduction has the potential to improve the accuracy of breeding selection
criteria. Research leading to sequencing of theequine genome has resulted in the identification ofa 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 testingof embryos provides a more effective method toselect for (or against) certain genetics. Recent andongoing research allows us to recover embryos nonsurgically from the uterus a week after conception
and test the conceptus for the presence or absenceof specific genes. The embryo can be cryopreserved
while molecular genetic testing is performed in thelaboratory and if test results are favorable, it canbe 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 carriersof some desirable genes) are completely removed
from breeding, selection of healthy embryos basedon pre-implantation genetic testing is the only
way to eradicate the disease. Because of its practical benefit to horse breeders, the technology ofpre-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, andtests 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).

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

sperm based on other genetics that can be used asa replacement or complement to pre-implantation
genetic testing of embryos. Preliminary resultsfrom studies using nanotechnology for sex-sortingin donkeys and other species appear to be promising. Logically, technologies that involve sperm
selection in the laboratory will always result in
limited number of sperm that can be used forbreeding. However, recent scientific and clinicaladvances make it possible to use a single spermfrom an infertile stallion and inject it into an
egg that has been retrieved by ultrasound guided
follicular aspiration from the ovary, culture theconceptus in a petri dish under controlled conditions and transfer the embryo into a recipientmare or back into the same oocyte donor mareat a later time. Intracytoplasmic sperm injection(ICSI) has become increasingly popular and asuitable method to use genetically valuable semenof poor quality or with restricted access becauseof disease or death of the stallion. Research to
improve the efficiency of this technology would
greatly benefit breeding operations that allow assisted reproduction.
Few, if any, breed registries accept foals resulting
from somatic cell cloning of an existing individual.
The technology is nevertheless offered for horses,
and has become popular among some horse owners that don’t need to register their foals. Althoughcloned horses have been used successfully as athletes, the greatest benefit of the technology may
be the possibility to produce an intact stallion as a
genetic copy of an existing gelding with a successful athletic career. It should be kept in mind thateven if the genetic make-up of the cloned copy
is identical to the original horse, the phenotype(looks and performance) may be different becauseof the influence of the environment that the embryo and fetus were exposed to in the test tube
and uterus of the surrogate mother (epigenetics).
The best prospective for the cloned intact stallion
may therefore, be for breeding purposes. In otherwords—an expensive way to put testicles back on
a gelding.
CONTACT:
Mats H.T. Troedsson, DVM, PhD, DACT, DECAR
m.troedsson@uky.edu(859) 218-1133
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

2

3

4

I N T E R N AT I O N A L

First Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
For the period under view, African horse sickness (AHS) was reported by Cameroon, Chad, theRepublic of South Africa (RSA), and Swaziland.
Swaziland reported four outbreaks of AHS, eachinvolving very limited numbers of horses. Twooutbreaks of AHS were confirmed in Cameroon
and Chad. Both outbreaks in Cameroon involved
working horses and donkeys, and horses wereprimarily affected in Chad. Incidence of the disease was above average in the RSA, especially inGauteng Province. Sporadic cases were recordedin the remaining provinces in the AHS infected
area. No cases were reported to date in the Western
Cape Province, either in the infected or diseasefree areas.
Equine influenza (EI) was confirmed in numerous countries in Europe (Belgium, Denmark,France, Germany, Ireland, the Netherlands andthe UK), West Africa (Burkina Faso, Ghana, Mali,
Nigeria, Niger, and Senegal), and the USA. In
Europe, the outbreaks primarily involved unvaccinated horses, but the disease also was observedin vaccinated horses. Strains of clade 1, Florida
sub-lineage of H3N8 EI virus were implicated.
The major impact of EI in West Africa was seen in
donkeys, in which thousands of cases were reportedwith very high fatality rates. Equine influenza isendemic in the USA; 57 outbreaks were confirmed
in eight states during the first quarter of 2019.
Strangles remains endemic in most countries:
France (33 outbreaks), New Zealand (one outbreak), Sweden (three outbreaks), the UK (oneoutbreak), and the USA in which the disease isendemic. Eighty-four outbreaks were diagnosed in
18 states, with multiple outbreaks in three states.
Equine herpesvirus 1 (EHV-1) related diseases were reported by Belgium, Canada, France,
Germany, Japan, Norway, Sweden, the UK, andthe USA. The number of confirmed outbreaks ofrespiratory disease ranged from one (Norway andSweden), two (Belgium, the UK and the USA),and four (France). Cases of EHV-1 abortion
were diagnosed in Belgium (one), Canada (two),France (five), Germany (one), Japan (eight), Sweden (two), the UK (four), and the USA (eleven).

Equine herpesvirus 1 neurologic disease wasreported by France (three outbreaks), Germany(three outbreaks), Sweden (three outbreaks, eachinvolving multiple cases), and the USA (13 outbreaks in eight states, three involving multiple
cases).
Equine herpesvirus 4 respiratory disease wasrecorded in Argentina, Belgium, and the RSA (oneoutbreak apiece), Sweden and the UK (each withseven outbreaks), France (36 outbreaks), and theUSA, in which the disease is endemic.
Equine herpesvirus 2 infection was reportedby the USA, in some instances associated withrespiratory disease.
Bulgaria, Canada, Peru, and the USA confirmed
outbreaks of equine infectious anemia. The number of cases ranged from one (Bulgaria, Peru) to fivein Canada. The USA recorded the disease in fivestates, with the number of cases by state ranging
from one to nine.
Equine piroplasmosis was reported by Ireland(a case of Babesia caballi infection in an imported
mare and her aborted foal) and the RSA in which
the disease is endemic.
Cases of leptospiral abortion were confirmed
by Belgium (one) and the USA (two). The USA
diagnosed four cases of nocardioform placentitis,
three associated with Amycolatopsis spp and one
with Crossiella equi infection, and four other casesof mucoid placentitis.
Two cases of equine coital exanthema wereconfirmed in the USA.
Clostridial enterocolitis was diagnosed inneonatal foals in the USA, five of which wereassociated with Clostridium perfringens infection.
Additionally, four cases of C. difficile infection
were confirmed.
Of neurological diseases reported during thefirst quarter of 2019, one case of rabies and ninecases of Eastern equine encephalomyelitis werereported by the USA, all but one in Florida. During the same period, the RSA confirmed one caseof West Nile virus infection and 60 cases of equine
encephalosis that occurred in a total of five provinces. Mexico reported 41 outbreaks of Westernequine encephalomyelitis in the state of Nayarit.
Fifty-three cases of the disease were recorded inthese outbreaks, including seven fatalities.

Changing Trends in Equine Reproduction

R

esearch advances in equine reproductive biology and health over the past 50 years havecontributed to improved fertility and breeding
efficiency in horses. The development of endocrine
and ultrasonography diagnostics aids the clinician
in determining potential fertility of mares and stallions. Follicular dysfunction and ovulation failure
can be diagnosed with high precision in mares, embryo and fetal development can be monitored from10 days after ovulation throughout gestation, andfetal/placental abnormalities diagnosed to identify
high-risk pregnancies. In stallions, biochemicaland genetic sperm abnormalities have been identified that previously remained undetected basedon traditional breeding soundness examinations.
Furthermore, testicular abnormalities and bloodflow can be determined with high accuracy byDoppler flow ultrasonography.
The current trend in horse breeding is characterized by a decline in mares that are bred and a
new focus on wellbeing of established pregnancies
as well as enhanced genetic selection with regards
to health and future performance of the foal. In
addition, great advances in the area of assisted
reproductive technologies offer numerous possibilities that were not available in the past.
Monitoring Healthy Pregnancy

Biomarkers for high-risk pregnancies and efficient treatments to prevent late pregnancy losses
are being investigated. As new potential markers
for unhealthy conditions are discovered, effective treatment options need to be developed. A
similar trend is seen with regards to endometritis
as well as the development of new diagnostics fordormant bacteria and uterine biofilms. While
new therapeutic regimens for endometritis often
include non-antibiotic alternatives or supplements,
most treatment options for high-risk pregnant
mares include long-term use of broad-spectrum
systemic antibiotics without the possibility of
performing bacterial sensitivity tests. There is a
global awareness of consequences when antibiotics are overused in human as well as veterinary
medicine—and equine reproduction is not an
exception. An overuse of antibiotics can lead tobacterial resistance and contribute to one of themost urgent public health issues today. New trends
in equine reproduction reflect these challenges toAssisted Reproduction

Assisted reproduction is not suitable to all
breeders. However, current knowledge andexpected 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 andsubfertile stallions, allowing for treatment of thesemen. 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 withtiming 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 bycentrifugation of their ejaculates and re-suspensionof the sperm in an extender with supportive nutrients. Furthermore, the quality of an ejaculate
can be enhanced through gradient centrifugationthat can separate “good” and “bad” sperm before
insemination. Further research to enhance ourunderstanding of relevant sperm biology andadvanced diagnostics to identify preferable sperm
populations in an ejaculate is expected to create aneed for robust and efficient technologies to selectsuperior sperm within an ejaculate.
Research that makes it possible to separate
x- and y- bearing sperm through flow cytometry(based on the fact that x-bearing sperm contains
more DNA), has been commercialized and iscurrently offered by specialized laboratories. The
method is very accurate, but efficiency is still quite
low and results in a low number of sex-sorted
sperm. This hurdle has been a limiting factor
for the method and more research is needed to
improve the technique. Recent research exploring
the use of nanotechnology to target specific sperm
DNA sequences has the potential to develop a
new efficient technology to select sperm for sexsorting, and maybe more importantly—to selectveterinary medicine, public health and the global
equine breeding industry, and additional nonantibiotic treatment options need to be developed.
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 (bloodlines) and make breeding decisions based on theseevaluations. As equine breeding has shifted fromquantity to a greater focus on quality, genetics andgenomic research in reproduction has the potential to improve the accuracy of breeding selection
criteria. Research leading to sequencing of theequine genome has resulted in the identification ofa 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 testingof embryos provides a more effective method toselect for (or against) certain genetics. Recent andongoing research allows us to recover embryos nonsurgically from the uterus a week after conception
and test the conceptus for the presence or absenceof specific genes. The embryo can be cryopreserved
while molecular genetic testing is performed in thelaboratory and if test results are favorable, it canbe 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 carriersof some desirable genes) are completely removed
from breeding, selection of healthy embryos basedon pre-implantation genetic testing is the only
way to eradicate the disease. Because of its practical benefit to horse breeders, the technology ofpre-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, andtests 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).

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

sperm based on other genetics that can be used asa replacement or complement to pre-implantation
genetic testing of embryos. Preliminary resultsfrom studies using nanotechnology for sex-sortingin donkeys and other species appear to be promising. Logically, technologies that involve sperm
selection in the laboratory will always result in
limited number of sperm that can be used forbreeding. However, recent scientific and clinicaladvances make it possible to use a single spermfrom an infertile stallion and inject it into an
egg that has been retrieved by ultrasound guided
follicular aspiration from the ovary, culture theconceptus in a petri dish under controlled conditions and transfer the embryo into a recipientmare or back into the same oocyte donor mareat a later time. Intracytoplasmic sperm injection(ICSI) has become increasingly popular and asuitable method to use genetically valuable semenof poor quality or with restricted access becauseof disease or death of the stallion. Research to
improve the efficiency of this technology would
greatly benefit breeding operations that allow assisted reproduction.
Few, if any, breed registries accept foals resulting
from somatic cell cloning of an existing individual.
The technology is nevertheless offered for horses,
and has become popular among some horse owners that don’t need to register their foals. Althoughcloned horses have been used successfully as athletes, the greatest benefit of the technology may
be the possibility to produce an intact stallion as a
genetic copy of an existing gelding with a successful athletic career. It should be kept in mind thateven if the genetic make-up of the cloned copy
is identical to the original horse, the phenotype(looks and performance) may be different becauseof the influence of the environment that the embryo and fetus were exposed to in the test tube
and uterus of the surrogate mother (epigenetics).
The best prospective for the cloned intact stallion
may therefore, be for breeding purposes. In otherwords—an expensive way to put testicles back on
a gelding.
CONTACT:
Mats H.T. Troedsson, DVM, PhD, DACT, DECAR
m.troedsson@uky.edu(859) 218-1133
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

2

3

4

I N T E R N AT I O N A L

First Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following equine disease outbreaks.
For the period under view, African horse sickness (AHS) was reported by Cameroon, Chad, theRepublic of South Africa (RSA), and Swaziland.
Swaziland reported four outbreaks of AHS, eachinvolving very limited numbers of horses. Twooutbreaks of AHS were confirmed in Cameroon
and Chad. Both outbreaks in Cameroon involved
working horses and donkeys, and horses wereprimarily affected in Chad. Incidence of the disease was above average in the RSA, especially inGauteng Province. Sporadic cases were recordedin the remaining provinces in the AHS infected
area. No cases were reported to date in the Western
Cape Province, either in the infected or diseasefree areas.
Equine influenza (EI) was confirmed in numerous countries in Europe (Belgium, Denmark,France, Germany, Ireland, the Netherlands andthe UK), West Africa (Burkina Faso, Ghana, Mali,
Nigeria, Niger, and Senegal), and the USA. In
Europe, the outbreaks primarily involved unvaccinated horses, but the disease also was observedin vaccinated horses. Strains of clade 1, Florida
sub-lineage of H3N8 EI virus were implicated.
The major impact of EI in West Africa was seen in
donkeys, in which thousands of cases were reportedwith very high fatality rates. Equine influenza isendemic in the USA; 57 outbreaks were confirmed
in eight states during the first quarter of 2019.
Strangles remains endemic in most countries:
France (33 outbreaks), New Zealand (one outbreak), Sweden (three outbreaks), the UK (oneoutbreak), and the USA in which the disease isendemic. Eighty-four outbreaks were diagnosed in
18 states, with multiple outbreaks in three states.
Equine herpesvirus 1 (EHV-1) related diseases were reported by Belgium, Canada, France,
Germany, Japan, Norway, Sweden, the UK, andthe USA. The number of confirmed outbreaks ofrespiratory disease ranged from one (Norway andSweden), two (Belgium, the UK and the USA),and four (France). Cases of EHV-1 abortion
were diagnosed in Belgium (one), Canada (two),France (five), Germany (one), Japan (eight), Sweden (two), the UK (four), and the USA (eleven).

Equine herpesvirus 1 neurologic disease wasreported by France (three outbreaks), Germany(three outbreaks), Sweden (three outbreaks, eachinvolving multiple cases), and the USA (13 outbreaks in eight states, three involving multiple
cases).
Equine herpesvirus 4 respiratory disease wasrecorded in Argentina, Belgium, and the RSA (oneoutbreak apiece), Sweden and the UK (each withseven outbreaks), France (36 outbreaks), and theUSA, in which the disease is endemic.
Equine herpesvirus 2 infection was reportedby the USA, in some instances associated withrespiratory disease.
Bulgaria, Canada, Peru, and the USA confirmed
outbreaks of equine infectious anemia. The number of cases ranged from one (Bulgaria, Peru) to fivein Canada. The USA recorded the disease in fivestates, with the number of cases by state ranging
from one to nine.
Equine piroplasmosis was reported by Ireland(a case of Babesia caballi infection in an imported
mare and her aborted foal) and the RSA in which
the disease is endemic.
Cases of leptospiral abortion were confirmed
by Belgium (one) and the USA (two). The USA
diagnosed four cases of nocardioform placentitis,
three associated with Amycolatopsis spp and one
with Crossiella equi infection, and four other casesof mucoid placentitis.
Two cases of equine coital exanthema wereconfirmed in the USA.
Clostridial enterocolitis was diagnosed inneonatal foals in the USA, five of which wereassociated with Clostridium perfringens infection.
Additionally, four cases of C. difficile infection
were confirmed.
Of neurological diseases reported during thefirst quarter of 2019, one case of rabies and ninecases of Eastern equine encephalomyelitis werereported by the USA, all but one in Florida. During the same period, the RSA confirmed one caseof West Nile virus infection and 60 cases of equine
encephalosis that occurred in a total of five provinces. Mexico reported 41 outbreaks of Westernequine encephalomyelitis in the state of Nayarit.
Fifty-three cases of the disease were recorded inthese outbreaks, including seven fatalities.

Changing Trends in Equine Reproduction

R

esearch advances in equine reproductive biology and health over the past 50 years havecontributed to improved fertility and breeding
efficiency in horses. The development of endocrine
and ultrasonography diagnostics aids the clinician
in determining potential fertility of mares and stallions. Follicular dysfunction and ovulation failure
can be diagnosed with high precision in mares, embryo and fetal development can be monitored from10 days after ovulation throughout gestation, andfetal/placental abnormalities diagnosed to identify
high-risk pregnancies. In stallions, biochemicaland genetic sperm abnormalities have been identified that previously remained undetected basedon traditional breeding soundness examinations.
Furthermore, testicular abnormalities and bloodflow can be determined with high accuracy byDoppler flow ultrasonography.
The current trend in horse breeding is characterized by a decline in mares that are bred and a
new focus on wellbeing of established pregnancies
as well as enhanced genetic selection with regards
to health and future performance of the foal. In
addition, great advances in the area of assisted
reproductive technologies offer numerous possibilities that were not available in the past.
Monitoring Healthy Pregnancy

Biomarkers for high-risk pregnancies and efficient treatments to prevent late pregnancy losses
are being investigated. As new potential markers
for unhealthy conditions are discovered, effective treatment options need to be developed. A
similar trend is seen with regards to endometritis
as well as the development of new diagnostics fordormant bacteria and uterine biofilms. While
new therapeutic regimens for endometritis often
include non-antibiotic alternatives or supplements,
most treatment options for high-risk pregnant
mares include long-term use of broad-spectrum
systemic antibiotics without the possibility of
performing bacterial sensitivity tests. There is a
global awareness of consequences when antibiotics are overused in human as well as veterinary
medicine—and equine reproduction is not an
exception. An overuse of antibiotics can lead tobacterial resistance and contribute to one of themost urgent public health issues today. New trends
in equine reproduction reflect these challenges toAssisted Reproduction

Assisted reproduction is not suitable to all
breeders. However, current knowledge andexpected 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 andsubfertile stallions, allowing for treatment of thesemen. 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 withtiming 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 bycentrifugation of their ejaculates and re-suspensionof the sperm in an extender with supportive nutrients. Furthermore, the quality of an ejaculate
can be enhanced through gradient centrifugationthat can separate “good” and “bad” sperm before
insemination. Further research to enhance ourunderstanding of relevant sperm biology andadvanced diagnostics to identify preferable sperm
populations in an ejaculate is expected to create aneed for robust and efficient technologies to selectsuperior sperm within an ejaculate.
Research that makes it possible to separate
x- and y- bearing sperm through flow cytometry(based on the fact that x-bearing sperm contains
more DNA), has been commercialized and iscurrently offered by specialized laboratories. The
method is very accurate, but efficiency is still quite
low and results in a low number of sex-sorted
sperm. This hurdle has been a limiting factor
for the method and more research is needed to
improve the technique. Recent research exploring
the use of nanotechnology to target specific sperm
DNA sequences has the potential to develop a
new efficient technology to select sperm for sexsorting, and maybe more importantly—to selectveterinary medicine, public health and the global
equine breeding industry, and additional nonantibiotic treatment options need to be developed.
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 (bloodlines) and make breeding decisions based on theseevaluations. As equine breeding has shifted fromquantity to a greater focus on quality, genetics andgenomic research in reproduction has the potential to improve the accuracy of breeding selection
criteria. Research leading to sequencing of theequine genome has resulted in the identification ofa 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 testingof embryos provides a more effective method toselect for (or against) certain genetics. Recent andongoing research allows us to recover embryos nonsurgically from the uterus a week after conception
and test the conceptus for the presence or absenceof specific genes. The embryo can be cryopreserved
while molecular genetic testing is performed in thelaboratory and if test results are favorable, it canbe 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 carriersof some desirable genes) are completely removed
from breeding, selection of healthy embryos basedon pre-implantation genetic testing is the only
way to eradicate the disease. Because of its practical benefit to horse breeders, the technology ofpre-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, andtests 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).

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

sperm based on other genetics that can be used asa replacement or complement to pre-implantation
genetic testing of embryos. Preliminary resultsfrom studies using nanotechnology for sex-sortingin donkeys and other species appear to be promising. Logically, technologies that involve sperm
selection in the laboratory will always result in
limited number of sperm that can be used forbreeding. However, recent scientific and clinicaladvances make it possible to use a single spermfrom an infertile stallion and inject it into an
egg that has been retrieved by ultrasound guided
follicular aspiration from the ovary, culture theconceptus in a petri dish under controlled conditions and transfer the embryo into a recipientmare or back into the same oocyte donor mareat a later time. Intracytoplasmic sperm injection(ICSI) has become increasingly popular and asuitable method to use genetically valuable semenof poor quality or with restricted access becauseof disease or death of the stallion. Research to
improve the efficiency of this technology would
greatly benefit breeding operations that allow assisted reproduction.
Few, if any, breed registries accept foals resulting
from somatic cell cloning of an existing individual.
The technology is nevertheless offered for horses,
and has become popular among some horse owners that don’t need to register their foals. Althoughcloned horses have been used successfully as athletes, the greatest benefit of the technology may
be the possibility to produce an intact stallion as a
genetic copy of an existing gelding with a successful athletic career. It should be kept in mind thateven if the genetic make-up of the cloned copy
is identical to the original horse, the phenotype(looks and performance) may be different becauseof the influence of the environment that the embryo and fetus were exposed to in the test tube
and uterus of the surrogate mother (epigenetics).
The best prospective for the cloned intact stallion
may therefore, be for breeding purposes. In otherwords—an expensive way to put testicles back on
a gelding.
CONTACT:
Mats H.T. Troedsson, DVM, PhD, DACT, DECAR
m.troedsson@uky.edu(859) 218-1133
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

Equine Disease Quarterly Newsletter

5

N AT I O N A L

Clostridial Myositis

C

lostridial myositis is a rare but serious bacterial infection, which causes inflammation anddeath of muscle and release of bacterial toxins into
the bloodstream. This condition is also referred
to as myonecrosis, malignant edema, and gas
gangrene. It occurs most often in horses that haverecently received an intramuscular injection. Clinical signs appear 6-72 hours following the injection,and horses initially exhibit acute swelling, heat, andpain of the affected area. The disease progresses
rapidly and the horse’s condition may decline
within hours. The affected animal exhibits signs ofsystemic toxemia; death can supervene rapidly insevere cases. Clostridial bacteria produce gas that
results in a characteristic emphysematous (bubbly) feel or crepitation of the region. Clostridial
myositis is a true medical emergency, with survival
linked to prompt intervention through aggressive
antibiotic treatment and wound debridement.
The Clostridium genus consists of over 150
known species of Gram-positive, anaerobic, sporeforming bacteria. The spore-forming ability ofthese bacteria allows survival for long periods oftime in the environment. When spores encounter alocation without oxygen, such as damaged muscle,
they are triggered to proliferate and produce exotoxins, which cause extensive tissue and vasculardamage. The clostridial species that commonly
cause myositis include C. perfringens, C. septicum
and C. chauvoei.
Clostridial myositis has been reported following
intramuscular inoculations of vaccines, ivermectin, antihistamines, phenylbutazone, vitamins,
prostaglandins, and most commonly, flunixin
meglumine. Infrequently, cases occur following
inadequate perivascular administration of compounds, foaling trauma, or puncture wounds. In a
study by Peek et al in 2003, stallions and Quarter
horses were overrepresented, and the authors hypothesized this might be due to the heavy musclingof these groups.
The mechanism by which the bacterial spores
arrive in the muscle of the horse is unknown.
It is possible spores are introduced at the time

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

JULY 2019
Volume 28, Number 3

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
First Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Changing Trends
in Equine
Reproduction  .  .  .  .  .  .  . 3National
Clostridial Myositis  .  . 5of injection. Another theory is that bacteria aretranslocated from their normal environment in
the intestine, in times of inflammation or colic
and arrive in the muscle via the bloodstream. No
association linking whether or not the injection site
is cleaned prior to injection and the developmentof myositis has been established. A higher incidence of myositis with irritating substances suchas nonsteroidal drugs and vitamins is reported,
potentially due to increased tissue damage andcreation of an oxygen-free environment.
Diagnosis involves aspirating a small amountof fluid for anaerobic culture and Gram-staining
to look for the presence of gram-positive rods. To
treat the infection, large incisions are made into themuscle and fascia to expose the bacteria to oxygenand debride dead tissue. General supportive careis critical because these bacteria produce toxinsthat have secondary effects on the horse, including the potential to reduce the contractility of theheart. Clostridial toxins may also result in anemia,
thrombocytopenia, and leukopenia. Horses arecommonly treated with high doses of intravenous
penicillin, intravenous fluids, cardiovascular sup-port, and wound care. Hyperbaric therapy, whereavailable, is suggested as an adjunct to routine
treatment.
Survival has been reported to range from 31%
to 73% and appears to be better for infections
with C. perfringens compared with C. septicum or
C. chauvoei. Horses that survive the initial toxemic
stages of disease have an improved prognosis. The
wounds created by a combination of infection andtreatment are usually large, and may take weeks
to months to heal entirely. Horses which do notsurvive show signs of intravascular coagulation andmulti-organ failure.
There is no definitive prevention for clostridial
myositis. When giving intramuscular injections,use large and well vascularized muscle groups, andwhen possible avoid giving irritating substances in
the muscle if there is an alternative route such asoral or intravenous administration.
CONTACT:
Rebecca Ruby, BVSc (dist), MSc, DACVP
Rebecca.Ruby@uky.edu(859) 257-8283
UK Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceIn an article contained in this issue of EDQ, Dr.
Troedsson nicely details advances in the scienceand practice of equine reproduction over the
past 50 years that have contributed to improved
fertility and breeding efficiency in the horse. It is
important to point out, however, that research conducted at the Kentucky Agricultural Experiment
Station at the University of Kentucky beginningover 100 years ago laid much of the groundworkfor understanding important diseases impacting
reproduction as well as the clinical evaluation ofstallions and mares for infertility. Beginning in
1911, Good and others worked to identify thecausative bacterium for outbreaks of infectious
abortion (Salmonella abortusequi). Subsequentdevelopment of a bacterin and control procedures
led to the eventual eradication of this importantcause of infectious abortions in the U.S. Research
by Dimock, later joined by Edwards and Bruner,
led to descriptions of techniques for the clinicalexamination of mares for pregnancy as well as adetailed description of clinical, bacteriologic andpathologic changes in the reproductive tract ofinfertile mares. This work provided the foundation
for recommendations related to breeding hygiene,
uterine infections, infertility as well as pregnancy
detection in mares. In 1933, research by this groupprovided early characterizations of equine (herpes)
virus abortion. They also conducted large studies
that characterized both infectious and noninfec-

tious causes of abortion in mares in Central Kentucky. Subsequent work by Doll, Bryans, and later
Allen in the Department of Animal Pathology at
UK lead to the development of the first live andinactivated virus vaccines for the control of equine
herpesvirus abortion in mares. In the mid-1950s,
Doll, Bryan, McCollum, and Crowe describedthe viral agent causing equine viral arteritis andabortion in mares with subsequent developmentof vaccination and control strategies based upon
the work of Timoney and McCollum in the mid1980s. Research by Loy and others led to a better
understanding of postpartum reproduction inmares, together with the use of artificial lighting
regimes and endocrine manipulation for control ofthe estrous cycle in mares. Although this chronology is incomplete and omits other significant research, I think that this historical perspective adds
to the work characterized in Dr. Troedsson’s article.
In particular, it demonstrates the need for researchexpertise and interest focused on reproduction in
the horse to address current problems as well as
unforeseen future problems related to equids.
CONTACT:
Barry A. Ball, D.V.M., Ph.D., D.A.C.T.
b.a.ball@uky.edu(859) 218-1141
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

Equine Disease Quarterly Newsletter

5

N AT I O N A L

Clostridial Myositis

C

lostridial myositis is a rare but serious bacterial infection, which causes inflammation anddeath of muscle and release of bacterial toxins into
the bloodstream. This condition is also referred
to as myonecrosis, malignant edema, and gas
gangrene. It occurs most often in horses that haverecently received an intramuscular injection. Clinical signs appear 6-72 hours following the injection,and horses initially exhibit acute swelling, heat, andpain of the affected area. The disease progresses
rapidly and the horse’s condition may decline
within hours. The affected animal exhibits signs ofsystemic toxemia; death can supervene rapidly insevere cases. Clostridial bacteria produce gas that
results in a characteristic emphysematous (bubbly) feel or crepitation of the region. Clostridial
myositis is a true medical emergency, with survival
linked to prompt intervention through aggressive
antibiotic treatment and wound debridement.
The Clostridium genus consists of over 150
known species of Gram-positive, anaerobic, sporeforming bacteria. The spore-forming ability ofthese bacteria allows survival for long periods oftime in the environment. When spores encounter alocation without oxygen, such as damaged muscle,
they are triggered to proliferate and produce exotoxins, which cause extensive tissue and vasculardamage. The clostridial species that commonly
cause myositis include C. perfringens, C. septicum
and C. chauvoei.
Clostridial myositis has been reported following
intramuscular inoculations of vaccines, ivermectin, antihistamines, phenylbutazone, vitamins,
prostaglandins, and most commonly, flunixin
meglumine. Infrequently, cases occur following
inadequate perivascular administration of compounds, foaling trauma, or puncture wounds. In a
study by Peek et al in 2003, stallions and Quarter
horses were overrepresented, and the authors hypothesized this might be due to the heavy musclingof these groups.
The mechanism by which the bacterial spores
arrive in the muscle of the horse is unknown.
It is possible spores are introduced at the time

STEVE PATTON, UK AGRICULTURAL COMMUNICATIONS

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

JULY 2019
Volume 28, Number 3

C O M M E N TA RY
IN THIS ISSUE
Commentary
International
First Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Changing Trends
in Equine
Reproduction  .  .  .  .  .  .  . 3National
Clostridial Myositis  .  . 5of injection. Another theory is that bacteria aretranslocated from their normal environment in
the intestine, in times of inflammation or colic
and arrive in the muscle via the bloodstream. No
association linking whether or not the injection site
is cleaned prior to injection and the developmentof myositis has been established. A higher incidence of myositis with irritating substances suchas nonsteroidal drugs and vitamins is reported,
potentially due to increased tissue damage andcreation of an oxygen-free environment.
Diagnosis involves aspirating a small amountof fluid for anaerobic culture and Gram-staining
to look for the presence of gram-positive rods. To
treat the infection, large incisions are made into themuscle and fascia to expose the bacteria to oxygenand debride dead tissue. General supportive careis critical because these bacteria produce toxinsthat have secondary effects on the horse, including the potential to reduce the contractility of theheart. Clostridial toxins may also result in anemia,
thrombocytopenia, and leukopenia. Horses arecommonly treated with high doses of intravenous
penicillin, intravenous fluids, cardiovascular sup-port, and wound care. Hyperbaric therapy, whereavailable, is suggested as an adjunct to routine
treatment.
Survival has been reported to range from 31%
to 73% and appears to be better for infections
with C. perfringens compared with C. septicum or
C. chauvoei. Horses that survive the initial toxemic
stages of disease have an improved prognosis. The
wounds created by a combination of infection andtreatment are usually large, and may take weeks
to months to heal entirely. Horses which do notsurvive show signs of intravascular coagulation andmulti-organ failure.
There is no definitive prevention for clostridial
myositis. When giving intramuscular injections,use large and well vascularized muscle groups, andwhen possible avoid giving irritating substances in
the muscle if there is an alternative route such asoral or intravenous administration.
CONTACT:
Rebecca Ruby, BVSc (dist), MSc, DACVP
Rebecca.Ruby@uky.edu(859) 257-8283
UK Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, KY

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceIn an article contained in this issue of EDQ, Dr.
Troedsson nicely details advances in the scienceand practice of equine reproduction over the
past 50 years that have contributed to improved
fertility and breeding efficiency in the horse. It is
important to point out, however, that research conducted at the Kentucky Agricultural Experiment
Station at the University of Kentucky beginningover 100 years ago laid much of the groundworkfor understanding important diseases impacting
reproduction as well as the clinical evaluation ofstallions and mares for infertility. Beginning in
1911, Good and others worked to identify thecausative bacterium for outbreaks of infectious
abortion (Salmonella abortusequi). Subsequentdevelopment of a bacterin and control procedures
led to the eventual eradication of this importantcause of infectious abortions in the U.S. Research
by Dimock, later joined by Edwards and Bruner,
led to descriptions of techniques for the clinicalexamination of mares for pregnancy as well as adetailed description of clinical, bacteriologic andpathologic changes in the reproductive tract ofinfertile mares. This work provided the foundation
for recommendations related to breeding hygiene,
uterine infections, infertility as well as pregnancy
detection in mares. In 1933, research by this groupprovided early characterizations of equine (herpes)
virus abortion. They also conducted large studies
that characterized both infectious and noninfec-

tious causes of abortion in mares in Central Kentucky. Subsequent work by Doll, Bryans, and later
Allen in the Department of Animal Pathology at
UK lead to the development of the first live andinactivated virus vaccines for the control of equine
herpesvirus abortion in mares. In the mid-1950s,
Doll, Bryan, McCollum, and Crowe describedthe viral agent causing equine viral arteritis andabortion in mares with subsequent developmentof vaccination and control strategies based upon
the work of Timoney and McCollum in the mid1980s. Research by Loy and others led to a better
understanding of postpartum reproduction inmares, together with the use of artificial lighting
regimes and endocrine manipulation for control ofthe estrous cycle in mares. Although this chronology is incomplete and omits other significant research, I think that this historical perspective adds
to the work characterized in Dr. Troedsson’s article.
In particular, it demonstrates the need for researchexpertise and interest focused on reproduction in
the horse to address current problems as well as
unforeseen future problems related to equids.
CONTACT:
Barry A. Ball, D.V.M., Ph.D., D.A.C.T.
b.a.ball@uky.edu(859) 218-1141
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY