-- Online Version -Equine Disease Quarterly Newsletter

5

available in the United States, they represent aneffective and non-invasive method for screening
individual donkeys and herd populations andwould undoubtedly further our understanding of
the epidemiology and transmission of besnoitiosis
in the United States.
There are no known effective treatments forequine besnoitiosis. Treatment with anti-protozoal
medications ponazuril, trimethoprim-sulfamethozazole, and nitazoxanide have not been effective.
The potential for natural recovery from besnoitiosis
and the long-term prognosis for infected animals

remains unknown. The author has followed several infected donkeys for the past 5 years, noneof which have spontaneously resolved. Althoughbesnoitiosis has not yet been reported in horses inNorth America, cases have been described in Africa, and the potential for similar infections in the
United States cannot be excluded as a possibility.

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

CONTACT:
Sally DeNotta, DVM, PhD, DACVIM
s.denotta@ufl.edu(352) 392-2229
College of Veterinary Medicine
University of Florida
Gainesville, Florida

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

JANUARY 2020
Volume 29, Number 1

C O M M E N TA RYT

KENTUCKY

Peripartum Death in MaresComplications associated with foaling are asignificant cause of morbidity and mortality
in both foals and mares. Even apparently normal
births can result in significant internal and external
injury to the mare. In extreme cases, these injuries
can be severe and result in death or require humane
euthanasia of the dam.
A review of diagnostic case submissions to the
University of Kentucky Veterinary Diagnostic
Laboratory was conducted to assess equine peripartum deaths during the 2017 and 2018 foaling
seasons. Mares that died secondary to foaling
complications or were humanely euthanized due
to significant parturition associated injury were
included.
During the two-year period, 121 cases of peripartum death were identified out of approximately
3,000 equine necropsy submissions. Cases werecategorized into five groups (gastrointestinal,
musculoskeletal, reproductive, vascular, and miscellaneous) based on the primary organ systemassociated with the cause of death. Submissions
began in December and extended into June ofboth years. Deaths occurred in multiple breeds,
but Thoroughbreds predominated.
Fatal lesions associated with the gastrointestinal tract were most common and occurred in 52(43%) cases. Diseases with the highest incidence
included cecal rupture (12%), colonic torsion(7%), colonic rupture (4%), rectal prolapse (3%),
cecal impaction (3%), gastric rupture (3%), rectal
tear (3%), and non-infectious inflammatory processes (3%). One to two cases of small intestinal

perforation, mesenteric rents and tears, and colonicdisplacement were also identified.
Fatal vascular lesions accounted for 24% of
peripartum deaths and included the No. 1 causeof death during the review period, rupture of theuterine artery. Ruptures of the uterine artery wereby far the most common vascular lesion (17%),frequently resulted in secondary hematoma formation in the broad ligament, a connective tissue
structure that supports the uterus, and hemoperitoneum. Infrequent ruptures were also associatedwith the internal iliac artery (3%), circumiliac
artery (1%), ovarian artery (1%), and aorta (1%).
Two cases of broad ligament hematoma were recorded, in which the exact location of the vascularrupture could not be determined.Direct injury to
the mare’s reproductive tract occurred in 22% of
the cases and frequently resulted in humane euthanasia. Uterine tear/rupture was most frequentin this category and occurred in 12% of the cases.
Less common reproductive injuries included uterine prolapse and vaginal lacerations, each of which
occurred in 3% of mares. Single cases of hydrops
pregnancy, uterine adhesions, uterine torsion, andsignificant vaginal hemorrhage were also noted.
Surprisingly, injuries to the musculoskeletal
system resulted in euthanasia of 10 (8%) mares.
Fractures (5%) were most common followed by individual cases of hip joint luxation, diaphragmatic
hernia, significant muscle trauma, and peripheral
nerve damage. Fractures were specifically associated with the pelvis, tibia, and femur and werenoted to occur in mares during dystocia events,

suffering post-foaling pain, and being transported
to a veterinary clinic.
The miscellaneous group included four sporadic
and individual cases that occurred in the peripartum time period. These cases included death or
euthanasia due to uncontrollable post-dystocia
pain, a presumed cardiovascular event following
dystocia, an anaphylactic drug reaction, and liverdisease of unknown cause.
Dystocia was specifically mentioned in theclinical history of 19% of the 121 cases. Although
the accuracy of this self-reported number is notdefinitive, it does emphasize that many injuries
during the foaling period are not associated withdifficult births.

In summary, equine death associated with thefoaling period is unfortunately common. The
underlying causes likely include a mixture of diseases associated with birthing trauma, pain, fetal
movement and positioning, and vascular changes
associated with gestation. Evaluation of mares during and following parturition is essential to rapidly
identify and treat this unique group of diseases.
CONTACT:
Dr. Alan Loynachanalan.loynachan@uky.edu(859)257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, Kentucky

he art of horse production is pattern recognition. The most obvious pattern is thatIN THIS ISSUE
offspring resemble their parents. These resemblances can be found in phenotypes such as size,
Commentary
conformation, durability, and performance. Using
phenotypes and pedigrees, breeders have applied
International
selection, resulting in profound changes in horses
Third Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2 since their domestication 5,500 years ago. Today,
hundreds of breed registries exist, reflecting diverse
Inbreeding and
Genomics .  .  .  .  .  .  .  .  .  .  . 3 goals among horse breeders. These interests spandivergent phenotypes related to racing, pulling,
National
jumping, dressage, performing special gaits, andBesnoitiosis incharacteristics associated with coat color or size.
Donkeys .  .  .  .  .  .  .  .  .  .  .  .  . 4 The commonality among these traits is they havea large genetic component. Foundation Stock were
Kentucky
identified exemplifying traits of interest. The path
Peripartum Deathin Mares .  .  .  .  .  .  .  .  .  .  .  .  . 5 to improvement has been to identify quality breeding stock, cross them to Foundation horses andselect the best for future breeding stock. As a result,Foundation Stock are represented many times inhorse pedigrees and contribute to the distinctive
phenotypic characteristics within those breeds.
Recently, a reference whole genome sequenceof the horse was determined. Scientists identified genes for discrete traits such as coat colors
and some hereditary diseases. However, despite
a great deal of research, no single gene has beenfound responsible for complex traits such as racing, jumping, and gait. This is not surprising sinceathletic performance involves a combination ofmuscle strength, cardiovascular capability, comCollege of Agriculture, petitiveness, and coordination. Yes, a few genes
Food and Environment
have been identified that influence performance
Department of(e.g., DMRT3 for gait and MSTN for sprintVeterinary Scienceing); however the development of champions
involves many other genes as well as the art of the
trainer and skill of the rider. This relationship isremarkably complex since variation exists despite
Lloyd’s—An international
generations of selection. The resilience of genetic
insurance market forvariation may reflect the diverse ways in which a
bloodstock and otherhorse can become a champion. Northern Dancer
specialist insurance.

and Secretariat were champion Thoroughbred
racehorses; however, while Northern Dancer was
relatively small in stature, Secretariat was renownedfor his large size and stride length. While the oldbreeding adage is “breed the best to the best andhope for the best,” the skill of the successful breeder
is to identify hereditary patterns among the best
and make judicious choices. There is no single
genetic test that will replace the skill of the breeder.
Genomic tools have the potential to improve therecognition of useful patterns. Horse genes are distributed among 32 pairs of chromosomes (see theimage in the online version of this issue at http://
gluck.ca.uky.edu/equine-disease-quarterly). Thesechromosomes contain the genetic material underselection. Genetic recombination occurs during
production of eggs and sperm in each generationthat divides these genetic blocks into subsets ofchromosomes. It is possible to identify the specificblock inherited from each parent and relate thoseblocks to blocks found in the grandparents. Likewise, one might even discern the blocks back to theFoundation Stock. Unfortunately, such a tool does
not yet exist for horses, but a similar commercial
application is used by people to identify the originof their ancestors. We anticipate horse breeders may
seek to use such a tool one day.
Today we can apply genomics to assess one of
the concerns of horse breeders, namely inbreeding.
As noted above, the establishment of breeds relieson the identification and use of Foundation Stock.
An unintended consequence of this is inbreeding
and the attendant risk of inbreeding depression andthe appearance of deleterious hereditary diseases.
The article in this issue, “Genomics and Inbreeding,” describes the concern and identifies ways inwhich genomics can be used to monitor inbreeding
and assist breed registries to anticipate problems.
CONTACT:
Ernest Bailey
ebailey@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

2

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

Third Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita HatchettCorrespondence 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.
Cases of African horse sickness decreased substantially in the Republic of South Africa (RSA)
during the period under review. Fewer than fivecases occurred in the Eastern Cape Province,
Mpumalanga and KwaZulu Natal; no cases werereported in the Western Cape Province.
Kuwait confirmed three subclinical cases ofglanders on pre-export testing.
Equine influenza was recorded in Belgium,
Denmark, France, Germany, Sudan, the UK, andthe USA. The number of outbreaks/cases variedwith fewer than five cases reported by Belgium,
Denmark, and Germany, to six outbreaks in
France, four of which involved multiple cases.
Sudan reported 700 cases with 107 deaths; cases
spread from south Darfur to east Darfur. The UK
recorded 59 outbreaks. The disease was reported
as endemic in the USA with outbreaks confirmed
in six states.
France, Germany, the Netherlands, Switzerland, the UK, and the USA reported outbreaksof strangles. The number of confirmed outbreaks
ranged from two in Switzerland, three in Germany,
15 in the Netherlands, and 27 in France. The UK
and the USA reported the disease as endemic, with
the USA recording strangles in 14 states.
Equine herpesvirus 1 (EHV-1) related diseases
were recorded by Belgium, Denmark, France,
Germany, Ireland, Switzerland, the Netherlands,
the UK, and the USA. Respiratory disease wasdiagnosed in Belgium (two outbreaks), Denmark(one outbreak), France (four outbreaks), Germany(one outbreak), Ireland (two outbreaks), the Netherlands (one outbreak) and the USA (numerous
outbreaks). Denmark reported one outbreak
involving four cases of EHV-1 abortion. EHV-1
myeloencephalopathy was confirmed by France(three outbreaks, one involving five cases of thedisease), Switzerland and the Netherlands (oneoutbreak apiece), and the USA (three outbreaks
each involving single cases).
Equine herpesvirus 4 respiratory disease was reported by Belgium, Germany, and the Netherlands(three outbreaks apiece); France (11 outbreaks);
Ireland, Japan, and Switzerland (one outbreakapiece); the UK (six outbreaks); and the USA(numerous outbreaks).
France, Poland, and the UK recorded cases of
equine arteritis virus infection. Two outbreaks wereconfirmed by France, represented by single casesof abortion and two cases of equine viral arteritis
in one of the outbreaks. Poland recorded one outbreak involving three cases of equine viral arteritis.
The UK confirmed infection in a subclinical carrier
stallion.
Equine infectious anemia was reported by
Canada (three outbreaks involving single cases, oneof which was clinical), France (two outbreaks, eachinvolving single cases), and the USA (14 outbreaks,
one of which involved 17 horses).
The USA confirmed five outbreaks of anthrax,
all in a high-risk region of Texas.RSA reported thatequine piroplasmosis was endemic in the country,with 29 cases recorded during the period underreview.
Contagious equine metritis was confirmed
by Denmark (case in a stallion), France (twooutbreaks, one involving a carrier stallion andanother causing metritis and abortion in a mare),and Germany (infection in a mare).
Three outbreaks of salmonellosis were recordedin the USA.
The USA reported 25 cases of equine neorickettsiosis involving three states. The vast majority
were in July and August in Kentucky.
Clostridial enterocolitis was recorded in theUSA, with confirmation of 13 cases of Clostridium
perfringens Type A toxin genotype and 15 cases of
C. difficile.
France reported eight outbreaks of rotavirus
infection, six involving single cases and two withtwo cases. The USA confirmed 22 cases of infection, principally in Kentucky, the preponderance
associated with the G14 virus genotype and a few
involving both G3 and G14 genotypes.
A single case of Lawsonia intracellularis infection
was reported by the USA.
Eastern equine encephalomyelitis was recordedin the USA with 76 cases confirmed in the third
quarter, the majority in Florida and Michigan.
West Nile encephalitis was reported by Austria(two cases), Brazil (three cases), Canada (one case),
France (four cases), Germany (eight cases), Greece(two cases), Italy (one case), and the USA (34 cases,of which 14 were in California).
RSA confirmed three cases of equine encephalosis.
Vesicular stomatitis (Indiana serogroup) was
confirmed on premises in seven states in the USA:
Colorado, Nebraska, New Mexico, Oklahoma,
Texas, Utah and Wyoming. A total of 1095 affected

premises were identified during the period underreview.
Rhodococcal-related disease was reported by
Belgium (one case) and the USA, in which thedisease is endemic. Twenty cases were diagnosed
in Kentucky; this is considered a significant underestimate of the actual incidence.
Germany and Switzerland reported single casesof ehrlichiosis.

3

4

powerful, and we can begin to seek genetic patterns
correlated with measures valued by horse owners.
The limitation for such studies is the quality andavailability of data for traits related to fertility,
conformation, durability and athleticism. Collecting these data and using genomics to identify
genes associated with these complex traits would
be a more sensible way to improve performance
rather than simply seeking to limit inbreeding.

CONTACT:
Ernest Bailey
ebailey@uky.edu
Ted Kalbfleischted.kalbfleisch@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky
Jessica Petersen
Jessica.petersen@unl.edu
University of Nebraska-Lincoln
Lincoln, Nebraska

Inbreeding and Genomics

I

nbreeding has played a key role in the improvement of livestock breeds, resulting in more
uniform populations with highly specialized performance traits. Selection for desirable traits entails
identifying individuals with superior performanceand often mating them to relatives (inbreeding)
who possess the same superior traits. The goal ofthis practice is to increase the frequency of thedesired characteristics and thus of the beneficial
genes in the offspring. At the same time, negative
consequences of inbreeding are well known. In
small populations such as captive bred species,
the loss of diversity associated with inbreeding isa major concern, and significant losses of diversity
may lead to extinction. The increased expressionof recessive deleterious genotypes can also lead toembryonic loss or other defects, some of which
can be fatal. Furthermore, inbreeding can leadto a phenomenon called inbreeding depression.
Inbreeding depression is commonly manifest inpoor performance of traits that are complex (dueto contributions of many different genes), such as
fertility and athleticism. Mindful of the dangers
inherent with inbreeding, breeders traditionallybalance the benefits and dangers of inbreedingby monitoring their breeding stock, culling poor
performers and avoiding matings of closely related
individuals.
Recently, genetic tools have become available
that provide an alternative approach to unambiguously quantify and manage inbreeding relative tothe traditional use of pedigrees. Today, a genomic
survey of a horse’s DNA may cost $70 to $180. A
comprehensive whole genome sequence, including analyses, may cost $1,000 to $2,500. So far,over 1,000 horses have had their entire DNA
sequenced in connection with research projects.
Those genome sequences have been used to identify the genetic bases of diseases, coat colors andeven some performance traits. Nevertheless, theoverall performance of horses is complex, involving over 20,000 genes and probably millions ofother functional elements. Studying genes one ata time is unlikely to be effective to significantly
improve performance. Genomic tools, however,make it possible to identify associations between
the genome and traits that contribute to successor which may cause problems.
One of the areas in which genomics excels isin determining levels of inbreeding. An animal’s
inbreeding coefficient is the likelihood that bothparents transmitted the same piece of DNA to theiroffspring that they each inherited from a common
ancestor. Traditionally, we measured inbreedingby identifying all common ancestors – those thatappear in the paternal and maternal sides of anindividual’s pedigree. After common ancestors are
identified, the relationship between the parents of
the individual in question can be calculated. Using
this method, on average, pedigree-based inbreeding
coefficients for Thoroughbred horses are reported
to be between 12.5%-13.5%, however individual
horses may have values that range from less than
5% to over 20%. When genomic measures havebeen made in other species, geneticists discoveredthat inbreeding levels calculated from pedigrees
are poorly correlated (50%-80%) with genomic
measures of inbreeding. This is not surprisingsince pedigrees inaccurately assume a random
and equal transmission of genes each generation.
Which variant of each gene is inherited, however,is not predictable. For example, full-siblings share,on average, 50% of their genes; however, at any
particular part of the genome they may share 0,50, or 100%. Further, genes are not randomly
distributed in a breed since selection practices areapplied in mating horses. If we are good breeders,the genetic constitution of our current generation
is not a random representation of the ancestors,
but rather, a selection of the genes contributing totheir success.
There are other ways to apply genomics to horse
breeding. As noted above, both the genome and thetraits we value are complex. Our genomic tools are

N AT I O N A L

Besnoitiosis in Donkeys

Besnoitiosis is a protozoan infection caused by
Besnoitia spp., which are cyst-forming coccidian parasites that affect multiple host species
worldwide. Besnoitia bennetti is the species known
to infect equids and has been reported in horses
and donkeys in Africa, Asia, and more recently, theUnited States and Europe. Equine besnoitiosis was
first reported in 1927 in four horses from Sudan.
The only reported cases of equine besnoitiosis in
North America have been in donkeys.
The life cycle of Besnoitia species involves botha definitive (predator) and intermediate (prey)host. Although a feline definitive host has been
identified for Besnoitia species known to infectseveral types of wildlife, attempts to demonstratea cat as the definitive host of B. bennetti have been
unsuccessful, thus precluding researchers from
elucidating the parasite’s life cycle and mode ofdisease transmission in donkeys. Clinical disease is characterized by a miliary dermatitis causedby pinpoint parasitic cysts in the skin, mucous

Figure 1. Scleral pearls (arrow) in an infected
donkey.
Matt Barton, Agricultural Communications

membranes, and conjunctiva. The skin over the
muzzle, nostrils, ears, perineum, and medial thighappears to be preferentially affected. One of themost unique features of besnoitiosis is the development of “scleral pearls,” which are cysts on thesclera of the eye (Figure 1). Cysts have also been infrequently identified in the testicles, nasopharynx,
larynx, trachea, and esophagus of infected donkeys.
Infected donkeys may also have generalized crusting dermatitis, poor hair coat, and/or focal areasof alopecia. Often affected donkeys have a historyof chronic dermatitis non-responsive to treatment
with antibiotics, ointments, medicated baths, etc.
In an epidemiologic investigation of besnoitiosis
in donkey herds across the United States, young
animals (average age 2 years) were at increased riskof infection when compared to older individuals.
Sex and breed were not associated with developing
besnoitiosis. The most common lesions in infected
donkeys were cysts in the nostrils (94%), perineum(69%) and sclera (81%). Some infected animals
remain seemingly otherwise healthy, while others
become cachexic and debilitated as a result of thedisease. The reason for this difference in host response to infection is unknown, but similar clinicalsubtypes are observed with bovine besnoitiosis in
European cattle herds.
The current gold standard for diagnosing besnoitiosis in donkeys is histologic identificationof Besnoitia cysts within the skin of individuals
displaying clinical lesions, generally achieved via
skin biopsy. B. bennetti can be detected in blood
via western blot and indirect fluorescent antibody
testing (IFAT), and antibody titers in donkeys
have been shown to be effective for identifying
infected donkeys. While these assays are not yet

2

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

Third Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita HatchettCorrespondence 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.
Cases of African horse sickness decreased substantially in the Republic of South Africa (RSA)
during the period under review. Fewer than fivecases occurred in the Eastern Cape Province,
Mpumalanga and KwaZulu Natal; no cases werereported in the Western Cape Province.
Kuwait confirmed three subclinical cases ofglanders on pre-export testing.
Equine influenza was recorded in Belgium,
Denmark, France, Germany, Sudan, the UK, andthe USA. The number of outbreaks/cases variedwith fewer than five cases reported by Belgium,
Denmark, and Germany, to six outbreaks in
France, four of which involved multiple cases.
Sudan reported 700 cases with 107 deaths; cases
spread from south Darfur to east Darfur. The UK
recorded 59 outbreaks. The disease was reported
as endemic in the USA with outbreaks confirmed
in six states.
France, Germany, the Netherlands, Switzerland, the UK, and the USA reported outbreaksof strangles. The number of confirmed outbreaks
ranged from two in Switzerland, three in Germany,
15 in the Netherlands, and 27 in France. The UK
and the USA reported the disease as endemic, with
the USA recording strangles in 14 states.
Equine herpesvirus 1 (EHV-1) related diseases
were recorded by Belgium, Denmark, France,
Germany, Ireland, Switzerland, the Netherlands,
the UK, and the USA. Respiratory disease wasdiagnosed in Belgium (two outbreaks), Denmark(one outbreak), France (four outbreaks), Germany(one outbreak), Ireland (two outbreaks), the Netherlands (one outbreak) and the USA (numerous
outbreaks). Denmark reported one outbreak
involving four cases of EHV-1 abortion. EHV-1
myeloencephalopathy was confirmed by France(three outbreaks, one involving five cases of thedisease), Switzerland and the Netherlands (oneoutbreak apiece), and the USA (three outbreaks
each involving single cases).
Equine herpesvirus 4 respiratory disease was reported by Belgium, Germany, and the Netherlands(three outbreaks apiece); France (11 outbreaks);
Ireland, Japan, and Switzerland (one outbreakapiece); the UK (six outbreaks); and the USA(numerous outbreaks).
France, Poland, and the UK recorded cases of
equine arteritis virus infection. Two outbreaks wereconfirmed by France, represented by single casesof abortion and two cases of equine viral arteritis
in one of the outbreaks. Poland recorded one outbreak involving three cases of equine viral arteritis.
The UK confirmed infection in a subclinical carrier
stallion.
Equine infectious anemia was reported by
Canada (three outbreaks involving single cases, oneof which was clinical), France (two outbreaks, eachinvolving single cases), and the USA (14 outbreaks,
one of which involved 17 horses).
The USA confirmed five outbreaks of anthrax,
all in a high-risk region of Texas.RSA reported thatequine piroplasmosis was endemic in the country,with 29 cases recorded during the period underreview.
Contagious equine metritis was confirmed
by Denmark (case in a stallion), France (twooutbreaks, one involving a carrier stallion andanother causing metritis and abortion in a mare),and Germany (infection in a mare).
Three outbreaks of salmonellosis were recordedin the USA.
The USA reported 25 cases of equine neorickettsiosis involving three states. The vast majority
were in July and August in Kentucky.
Clostridial enterocolitis was recorded in theUSA, with confirmation of 13 cases of Clostridium
perfringens Type A toxin genotype and 15 cases of
C. difficile.
France reported eight outbreaks of rotavirus
infection, six involving single cases and two withtwo cases. The USA confirmed 22 cases of infection, principally in Kentucky, the preponderance
associated with the G14 virus genotype and a few
involving both G3 and G14 genotypes.
A single case of Lawsonia intracellularis infection
was reported by the USA.
Eastern equine encephalomyelitis was recordedin the USA with 76 cases confirmed in the third
quarter, the majority in Florida and Michigan.
West Nile encephalitis was reported by Austria(two cases), Brazil (three cases), Canada (one case),
France (four cases), Germany (eight cases), Greece(two cases), Italy (one case), and the USA (34 cases,of which 14 were in California).
RSA confirmed three cases of equine encephalosis.
Vesicular stomatitis (Indiana serogroup) was
confirmed on premises in seven states in the USA:
Colorado, Nebraska, New Mexico, Oklahoma,
Texas, Utah and Wyoming. A total of 1095 affected

premises were identified during the period underreview.
Rhodococcal-related disease was reported by
Belgium (one case) and the USA, in which thedisease is endemic. Twenty cases were diagnosed
in Kentucky; this is considered a significant underestimate of the actual incidence.
Germany and Switzerland reported single casesof ehrlichiosis.

3

4

powerful, and we can begin to seek genetic patterns
correlated with measures valued by horse owners.
The limitation for such studies is the quality andavailability of data for traits related to fertility,
conformation, durability and athleticism. Collecting these data and using genomics to identify
genes associated with these complex traits would
be a more sensible way to improve performance
rather than simply seeking to limit inbreeding.

CONTACT:
Ernest Bailey
ebailey@uky.edu
Ted Kalbfleischted.kalbfleisch@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky
Jessica Petersen
Jessica.petersen@unl.edu
University of Nebraska-Lincoln
Lincoln, Nebraska

Inbreeding and Genomics

I

nbreeding has played a key role in the improvement of livestock breeds, resulting in more
uniform populations with highly specialized performance traits. Selection for desirable traits entails
identifying individuals with superior performanceand often mating them to relatives (inbreeding)
who possess the same superior traits. The goal ofthis practice is to increase the frequency of thedesired characteristics and thus of the beneficial
genes in the offspring. At the same time, negative
consequences of inbreeding are well known. In
small populations such as captive bred species,
the loss of diversity associated with inbreeding isa major concern, and significant losses of diversity
may lead to extinction. The increased expressionof recessive deleterious genotypes can also lead toembryonic loss or other defects, some of which
can be fatal. Furthermore, inbreeding can leadto a phenomenon called inbreeding depression.
Inbreeding depression is commonly manifest inpoor performance of traits that are complex (dueto contributions of many different genes), such as
fertility and athleticism. Mindful of the dangers
inherent with inbreeding, breeders traditionallybalance the benefits and dangers of inbreedingby monitoring their breeding stock, culling poor
performers and avoiding matings of closely related
individuals.
Recently, genetic tools have become available
that provide an alternative approach to unambiguously quantify and manage inbreeding relative tothe traditional use of pedigrees. Today, a genomic
survey of a horse’s DNA may cost $70 to $180. A
comprehensive whole genome sequence, including analyses, may cost $1,000 to $2,500. So far,over 1,000 horses have had their entire DNA
sequenced in connection with research projects.
Those genome sequences have been used to identify the genetic bases of diseases, coat colors andeven some performance traits. Nevertheless, theoverall performance of horses is complex, involving over 20,000 genes and probably millions ofother functional elements. Studying genes one ata time is unlikely to be effective to significantly
improve performance. Genomic tools, however,make it possible to identify associations between
the genome and traits that contribute to successor which may cause problems.
One of the areas in which genomics excels isin determining levels of inbreeding. An animal’s
inbreeding coefficient is the likelihood that bothparents transmitted the same piece of DNA to theiroffspring that they each inherited from a common
ancestor. Traditionally, we measured inbreedingby identifying all common ancestors – those thatappear in the paternal and maternal sides of anindividual’s pedigree. After common ancestors are
identified, the relationship between the parents of
the individual in question can be calculated. Using
this method, on average, pedigree-based inbreeding
coefficients for Thoroughbred horses are reported
to be between 12.5%-13.5%, however individual
horses may have values that range from less than
5% to over 20%. When genomic measures havebeen made in other species, geneticists discoveredthat inbreeding levels calculated from pedigrees
are poorly correlated (50%-80%) with genomic
measures of inbreeding. This is not surprisingsince pedigrees inaccurately assume a random
and equal transmission of genes each generation.
Which variant of each gene is inherited, however,is not predictable. For example, full-siblings share,on average, 50% of their genes; however, at any
particular part of the genome they may share 0,50, or 100%. Further, genes are not randomly
distributed in a breed since selection practices areapplied in mating horses. If we are good breeders,the genetic constitution of our current generation
is not a random representation of the ancestors,
but rather, a selection of the genes contributing totheir success.
There are other ways to apply genomics to horse
breeding. As noted above, both the genome and thetraits we value are complex. Our genomic tools are

N AT I O N A L

Besnoitiosis in Donkeys

Besnoitiosis is a protozoan infection caused by
Besnoitia spp., which are cyst-forming coccidian parasites that affect multiple host species
worldwide. Besnoitia bennetti is the species known
to infect equids and has been reported in horses
and donkeys in Africa, Asia, and more recently, theUnited States and Europe. Equine besnoitiosis was
first reported in 1927 in four horses from Sudan.
The only reported cases of equine besnoitiosis in
North America have been in donkeys.
The life cycle of Besnoitia species involves botha definitive (predator) and intermediate (prey)host. Although a feline definitive host has been
identified for Besnoitia species known to infectseveral types of wildlife, attempts to demonstratea cat as the definitive host of B. bennetti have been
unsuccessful, thus precluding researchers from
elucidating the parasite’s life cycle and mode ofdisease transmission in donkeys. Clinical disease is characterized by a miliary dermatitis causedby pinpoint parasitic cysts in the skin, mucous

Figure 1. Scleral pearls (arrow) in an infected
donkey.
Matt Barton, Agricultural Communications

membranes, and conjunctiva. The skin over the
muzzle, nostrils, ears, perineum, and medial thighappears to be preferentially affected. One of themost unique features of besnoitiosis is the development of “scleral pearls,” which are cysts on thesclera of the eye (Figure 1). Cysts have also been infrequently identified in the testicles, nasopharynx,
larynx, trachea, and esophagus of infected donkeys.
Infected donkeys may also have generalized crusting dermatitis, poor hair coat, and/or focal areasof alopecia. Often affected donkeys have a historyof chronic dermatitis non-responsive to treatment
with antibiotics, ointments, medicated baths, etc.
In an epidemiologic investigation of besnoitiosis
in donkey herds across the United States, young
animals (average age 2 years) were at increased riskof infection when compared to older individuals.
Sex and breed were not associated with developing
besnoitiosis. The most common lesions in infected
donkeys were cysts in the nostrils (94%), perineum(69%) and sclera (81%). Some infected animals
remain seemingly otherwise healthy, while others
become cachexic and debilitated as a result of thedisease. The reason for this difference in host response to infection is unknown, but similar clinicalsubtypes are observed with bovine besnoitiosis in
European cattle herds.
The current gold standard for diagnosing besnoitiosis in donkeys is histologic identificationof Besnoitia cysts within the skin of individuals
displaying clinical lesions, generally achieved via
skin biopsy. B. bennetti can be detected in blood
via western blot and indirect fluorescent antibody
testing (IFAT), and antibody titers in donkeys
have been shown to be effective for identifying
infected donkeys. While these assays are not yet

2

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

Third Quarter 2019T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita HatchettCorrespondence 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.
Cases of African horse sickness decreased substantially in the Republic of South Africa (RSA)
during the period under review. Fewer than fivecases occurred in the Eastern Cape Province,
Mpumalanga and KwaZulu Natal; no cases werereported in the Western Cape Province.
Kuwait confirmed three subclinical cases ofglanders on pre-export testing.
Equine influenza was recorded in Belgium,
Denmark, France, Germany, Sudan, the UK, andthe USA. The number of outbreaks/cases variedwith fewer than five cases reported by Belgium,
Denmark, and Germany, to six outbreaks in
France, four of which involved multiple cases.
Sudan reported 700 cases with 107 deaths; cases
spread from south Darfur to east Darfur. The UK
recorded 59 outbreaks. The disease was reported
as endemic in the USA with outbreaks confirmed
in six states.
France, Germany, the Netherlands, Switzerland, the UK, and the USA reported outbreaksof strangles. The number of confirmed outbreaks
ranged from two in Switzerland, three in Germany,
15 in the Netherlands, and 27 in France. The UK
and the USA reported the disease as endemic, with
the USA recording strangles in 14 states.
Equine herpesvirus 1 (EHV-1) related diseases
were recorded by Belgium, Denmark, France,
Germany, Ireland, Switzerland, the Netherlands,
the UK, and the USA. Respiratory disease wasdiagnosed in Belgium (two outbreaks), Denmark(one outbreak), France (four outbreaks), Germany(one outbreak), Ireland (two outbreaks), the Netherlands (one outbreak) and the USA (numerous
outbreaks). Denmark reported one outbreak
involving four cases of EHV-1 abortion. EHV-1
myeloencephalopathy was confirmed by France(three outbreaks, one involving five cases of thedisease), Switzerland and the Netherlands (oneoutbreak apiece), and the USA (three outbreaks
each involving single cases).
Equine herpesvirus 4 respiratory disease was reported by Belgium, Germany, and the Netherlands(three outbreaks apiece); France (11 outbreaks);
Ireland, Japan, and Switzerland (one outbreakapiece); the UK (six outbreaks); and the USA(numerous outbreaks).
France, Poland, and the UK recorded cases of
equine arteritis virus infection. Two outbreaks wereconfirmed by France, represented by single casesof abortion and two cases of equine viral arteritis
in one of the outbreaks. Poland recorded one outbreak involving three cases of equine viral arteritis.
The UK confirmed infection in a subclinical carrier
stallion.
Equine infectious anemia was reported by
Canada (three outbreaks involving single cases, oneof which was clinical), France (two outbreaks, eachinvolving single cases), and the USA (14 outbreaks,
one of which involved 17 horses).
The USA confirmed five outbreaks of anthrax,
all in a high-risk region of Texas.RSA reported thatequine piroplasmosis was endemic in the country,with 29 cases recorded during the period underreview.
Contagious equine metritis was confirmed
by Denmark (case in a stallion), France (twooutbreaks, one involving a carrier stallion andanother causing metritis and abortion in a mare),and Germany (infection in a mare).
Three outbreaks of salmonellosis were recordedin the USA.
The USA reported 25 cases of equine neorickettsiosis involving three states. The vast majority
were in July and August in Kentucky.
Clostridial enterocolitis was recorded in theUSA, with confirmation of 13 cases of Clostridium
perfringens Type A toxin genotype and 15 cases of
C. difficile.
France reported eight outbreaks of rotavirus
infection, six involving single cases and two withtwo cases. The USA confirmed 22 cases of infection, principally in Kentucky, the preponderance
associated with the G14 virus genotype and a few
involving both G3 and G14 genotypes.
A single case of Lawsonia intracellularis infection
was reported by the USA.
Eastern equine encephalomyelitis was recordedin the USA with 76 cases confirmed in the third
quarter, the majority in Florida and Michigan.
West Nile encephalitis was reported by Austria(two cases), Brazil (three cases), Canada (one case),
France (four cases), Germany (eight cases), Greece(two cases), Italy (one case), and the USA (34 cases,of which 14 were in California).
RSA confirmed three cases of equine encephalosis.
Vesicular stomatitis (Indiana serogroup) was
confirmed on premises in seven states in the USA:
Colorado, Nebraska, New Mexico, Oklahoma,
Texas, Utah and Wyoming. A total of 1095 affected

premises were identified during the period underreview.
Rhodococcal-related disease was reported by
Belgium (one case) and the USA, in which thedisease is endemic. Twenty cases were diagnosed
in Kentucky; this is considered a significant underestimate of the actual incidence.
Germany and Switzerland reported single casesof ehrlichiosis.

3

4

powerful, and we can begin to seek genetic patterns
correlated with measures valued by horse owners.
The limitation for such studies is the quality andavailability of data for traits related to fertility,
conformation, durability and athleticism. Collecting these data and using genomics to identify
genes associated with these complex traits would
be a more sensible way to improve performance
rather than simply seeking to limit inbreeding.

CONTACT:
Ernest Bailey
ebailey@uky.edu
Ted Kalbfleischted.kalbfleisch@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky
Jessica Petersen
Jessica.petersen@unl.edu
University of Nebraska-Lincoln
Lincoln, Nebraska

Inbreeding and Genomics

I

nbreeding has played a key role in the improvement of livestock breeds, resulting in more
uniform populations with highly specialized performance traits. Selection for desirable traits entails
identifying individuals with superior performanceand often mating them to relatives (inbreeding)
who possess the same superior traits. The goal ofthis practice is to increase the frequency of thedesired characteristics and thus of the beneficial
genes in the offspring. At the same time, negative
consequences of inbreeding are well known. In
small populations such as captive bred species,
the loss of diversity associated with inbreeding isa major concern, and significant losses of diversity
may lead to extinction. The increased expressionof recessive deleterious genotypes can also lead toembryonic loss or other defects, some of which
can be fatal. Furthermore, inbreeding can leadto a phenomenon called inbreeding depression.
Inbreeding depression is commonly manifest inpoor performance of traits that are complex (dueto contributions of many different genes), such as
fertility and athleticism. Mindful of the dangers
inherent with inbreeding, breeders traditionallybalance the benefits and dangers of inbreedingby monitoring their breeding stock, culling poor
performers and avoiding matings of closely related
individuals.
Recently, genetic tools have become available
that provide an alternative approach to unambiguously quantify and manage inbreeding relative tothe traditional use of pedigrees. Today, a genomic
survey of a horse’s DNA may cost $70 to $180. A
comprehensive whole genome sequence, including analyses, may cost $1,000 to $2,500. So far,over 1,000 horses have had their entire DNA
sequenced in connection with research projects.
Those genome sequences have been used to identify the genetic bases of diseases, coat colors andeven some performance traits. Nevertheless, theoverall performance of horses is complex, involving over 20,000 genes and probably millions ofother functional elements. Studying genes one ata time is unlikely to be effective to significantly
improve performance. Genomic tools, however,make it possible to identify associations between
the genome and traits that contribute to successor which may cause problems.
One of the areas in which genomics excels isin determining levels of inbreeding. An animal’s
inbreeding coefficient is the likelihood that bothparents transmitted the same piece of DNA to theiroffspring that they each inherited from a common
ancestor. Traditionally, we measured inbreedingby identifying all common ancestors – those thatappear in the paternal and maternal sides of anindividual’s pedigree. After common ancestors are
identified, the relationship between the parents of
the individual in question can be calculated. Using
this method, on average, pedigree-based inbreeding
coefficients for Thoroughbred horses are reported
to be between 12.5%-13.5%, however individual
horses may have values that range from less than
5% to over 20%. When genomic measures havebeen made in other species, geneticists discoveredthat inbreeding levels calculated from pedigrees
are poorly correlated (50%-80%) with genomic
measures of inbreeding. This is not surprisingsince pedigrees inaccurately assume a random
and equal transmission of genes each generation.
Which variant of each gene is inherited, however,is not predictable. For example, full-siblings share,on average, 50% of their genes; however, at any
particular part of the genome they may share 0,50, or 100%. Further, genes are not randomly
distributed in a breed since selection practices areapplied in mating horses. If we are good breeders,the genetic constitution of our current generation
is not a random representation of the ancestors,
but rather, a selection of the genes contributing totheir success.
There are other ways to apply genomics to horse
breeding. As noted above, both the genome and thetraits we value are complex. Our genomic tools are

N AT I O N A L

Besnoitiosis in Donkeys

Besnoitiosis is a protozoan infection caused by
Besnoitia spp., which are cyst-forming coccidian parasites that affect multiple host species
worldwide. Besnoitia bennetti is the species known
to infect equids and has been reported in horses
and donkeys in Africa, Asia, and more recently, theUnited States and Europe. Equine besnoitiosis was
first reported in 1927 in four horses from Sudan.
The only reported cases of equine besnoitiosis in
North America have been in donkeys.
The life cycle of Besnoitia species involves botha definitive (predator) and intermediate (prey)host. Although a feline definitive host has been
identified for Besnoitia species known to infectseveral types of wildlife, attempts to demonstratea cat as the definitive host of B. bennetti have been
unsuccessful, thus precluding researchers from
elucidating the parasite’s life cycle and mode ofdisease transmission in donkeys. Clinical disease is characterized by a miliary dermatitis causedby pinpoint parasitic cysts in the skin, mucous

Figure 1. Scleral pearls (arrow) in an infected
donkey.
Matt Barton, Agricultural Communications

membranes, and conjunctiva. The skin over the
muzzle, nostrils, ears, perineum, and medial thighappears to be preferentially affected. One of themost unique features of besnoitiosis is the development of “scleral pearls,” which are cysts on thesclera of the eye (Figure 1). Cysts have also been infrequently identified in the testicles, nasopharynx,
larynx, trachea, and esophagus of infected donkeys.
Infected donkeys may also have generalized crusting dermatitis, poor hair coat, and/or focal areasof alopecia. Often affected donkeys have a historyof chronic dermatitis non-responsive to treatment
with antibiotics, ointments, medicated baths, etc.
In an epidemiologic investigation of besnoitiosis
in donkey herds across the United States, young
animals (average age 2 years) were at increased riskof infection when compared to older individuals.
Sex and breed were not associated with developing
besnoitiosis. The most common lesions in infected
donkeys were cysts in the nostrils (94%), perineum(69%) and sclera (81%). Some infected animals
remain seemingly otherwise healthy, while others
become cachexic and debilitated as a result of thedisease. The reason for this difference in host response to infection is unknown, but similar clinicalsubtypes are observed with bovine besnoitiosis in
European cattle herds.
The current gold standard for diagnosing besnoitiosis in donkeys is histologic identificationof Besnoitia cysts within the skin of individuals
displaying clinical lesions, generally achieved via
skin biopsy. B. bennetti can be detected in blood
via western blot and indirect fluorescent antibody
testing (IFAT), and antibody titers in donkeys
have been shown to be effective for identifying
infected donkeys. While these assays are not yetEquine Disease Quarterly Newsletter

5

available in the United States, they represent aneffective and non-invasive method for screening
individual donkeys and herd populations andwould undoubtedly further our understanding of
the epidemiology and transmission of besnoitiosis
in the United States.
There are no known effective treatments forequine besnoitiosis. Treatment with anti-protozoal
medications ponazuril, trimethoprim-sulfamethozazole, and nitazoxanide have not been effective.
The potential for natural recovery from besnoitiosis
and the long-term prognosis for infected animals

remains unknown. The author has followed several infected donkeys for the past 5 years, noneof which have spontaneously resolved. Althoughbesnoitiosis has not yet been reported in horses inNorth America, cases have been described in Africa, and the potential for similar infections in the
United States cannot be excluded as a possibility.

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

CONTACT:
Sally DeNotta, DVM, PhD, DACVIM
s.denotta@ufl.edu(352) 392-2229
College of Veterinary Medicine
University of Florida
Gainesville, Florida

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

JANUARY 2020
Volume 29, Number 1

C O M M E N TA RYT

KENTUCKY

Peripartum Death in MaresComplications associated with foaling are asignificant cause of morbidity and mortality
in both foals and mares. Even apparently normal
births can result in significant internal and external
injury to the mare. In extreme cases, these injuries
can be severe and result in death or require humane
euthanasia of the dam.
A review of diagnostic case submissions to the
University of Kentucky Veterinary Diagnostic
Laboratory was conducted to assess equine peripartum deaths during the 2017 and 2018 foaling
seasons. Mares that died secondary to foaling
complications or were humanely euthanized due
to significant parturition associated injury were
included.
During the two-year period, 121 cases of peripartum death were identified out of approximately
3,000 equine necropsy submissions. Cases werecategorized into five groups (gastrointestinal,
musculoskeletal, reproductive, vascular, and miscellaneous) based on the primary organ systemassociated with the cause of death. Submissions
began in December and extended into June ofboth years. Deaths occurred in multiple breeds,
but Thoroughbreds predominated.
Fatal lesions associated with the gastrointestinal tract were most common and occurred in 52(43%) cases. Diseases with the highest incidence
included cecal rupture (12%), colonic torsion(7%), colonic rupture (4%), rectal prolapse (3%),
cecal impaction (3%), gastric rupture (3%), rectal
tear (3%), and non-infectious inflammatory processes (3%). One to two cases of small intestinal

perforation, mesenteric rents and tears, and colonicdisplacement were also identified.
Fatal vascular lesions accounted for 24% of
peripartum deaths and included the No. 1 causeof death during the review period, rupture of theuterine artery. Ruptures of the uterine artery wereby far the most common vascular lesion (17%),frequently resulted in secondary hematoma formation in the broad ligament, a connective tissue
structure that supports the uterus, and hemoperitoneum. Infrequent ruptures were also associatedwith the internal iliac artery (3%), circumiliac
artery (1%), ovarian artery (1%), and aorta (1%).
Two cases of broad ligament hematoma were recorded, in which the exact location of the vascularrupture could not be determined.Direct injury to
the mare’s reproductive tract occurred in 22% of
the cases and frequently resulted in humane euthanasia. Uterine tear/rupture was most frequentin this category and occurred in 12% of the cases.
Less common reproductive injuries included uterine prolapse and vaginal lacerations, each of which
occurred in 3% of mares. Single cases of hydrops
pregnancy, uterine adhesions, uterine torsion, andsignificant vaginal hemorrhage were also noted.
Surprisingly, injuries to the musculoskeletal
system resulted in euthanasia of 10 (8%) mares.
Fractures (5%) were most common followed by individual cases of hip joint luxation, diaphragmatic
hernia, significant muscle trauma, and peripheral
nerve damage. Fractures were specifically associated with the pelvis, tibia, and femur and werenoted to occur in mares during dystocia events,

suffering post-foaling pain, and being transported
to a veterinary clinic.
The miscellaneous group included four sporadic
and individual cases that occurred in the peripartum time period. These cases included death or
euthanasia due to uncontrollable post-dystocia
pain, a presumed cardiovascular event following
dystocia, an anaphylactic drug reaction, and liverdisease of unknown cause.
Dystocia was specifically mentioned in theclinical history of 19% of the 121 cases. Although
the accuracy of this self-reported number is notdefinitive, it does emphasize that many injuries
during the foaling period are not associated withdifficult births.

In summary, equine death associated with thefoaling period is unfortunately common. The
underlying causes likely include a mixture of diseases associated with birthing trauma, pain, fetal
movement and positioning, and vascular changes
associated with gestation. Evaluation of mares during and following parturition is essential to rapidly
identify and treat this unique group of diseases.
CONTACT:
Dr. Alan Loynachanalan.loynachan@uky.edu(859)257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, Kentucky

he art of horse production is pattern recognition. The most obvious pattern is thatIN THIS ISSUE
offspring resemble their parents. These resemblances can be found in phenotypes such as size,
Commentary
conformation, durability, and performance. Using
phenotypes and pedigrees, breeders have applied
International
selection, resulting in profound changes in horses
Third Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2 since their domestication 5,500 years ago. Today,
hundreds of breed registries exist, reflecting diverse
Inbreeding and
Genomics .  .  .  .  .  .  .  .  .  .  . 3 goals among horse breeders. These interests spandivergent phenotypes related to racing, pulling,
National
jumping, dressage, performing special gaits, andBesnoitiosis incharacteristics associated with coat color or size.
Donkeys .  .  .  .  .  .  .  .  .  .  .  .  . 4 The commonality among these traits is they havea large genetic component. Foundation Stock were
Kentucky
identified exemplifying traits of interest. The path
Peripartum Deathin Mares .  .  .  .  .  .  .  .  .  .  .  .  . 5 to improvement has been to identify quality breeding stock, cross them to Foundation horses andselect the best for future breeding stock. As a result,Foundation Stock are represented many times inhorse pedigrees and contribute to the distinctive
phenotypic characteristics within those breeds.
Recently, a reference whole genome sequenceof the horse was determined. Scientists identified genes for discrete traits such as coat colors
and some hereditary diseases. However, despite
a great deal of research, no single gene has beenfound responsible for complex traits such as racing, jumping, and gait. This is not surprising sinceathletic performance involves a combination ofmuscle strength, cardiovascular capability, comCollege of Agriculture, petitiveness, and coordination. Yes, a few genes
Food and Environment
have been identified that influence performance
Department of(e.g., DMRT3 for gait and MSTN for sprintVeterinary Scienceing); however the development of champions
involves many other genes as well as the art of the
trainer and skill of the rider. This relationship isremarkably complex since variation exists despite
Lloyd’s—An international
generations of selection. The resilience of genetic
insurance market forvariation may reflect the diverse ways in which a
bloodstock and otherhorse can become a champion. Northern Dancer
specialist insurance.

and Secretariat were champion Thoroughbred
racehorses; however, while Northern Dancer was
relatively small in stature, Secretariat was renownedfor his large size and stride length. While the oldbreeding adage is “breed the best to the best andhope for the best,” the skill of the successful breeder
is to identify hereditary patterns among the best
and make judicious choices. There is no single
genetic test that will replace the skill of the breeder.
Genomic tools have the potential to improve therecognition of useful patterns. Horse genes are distributed among 32 pairs of chromosomes (see theimage in the online version of this issue at http://
gluck.ca.uky.edu/equine-disease-quarterly). Thesechromosomes contain the genetic material underselection. Genetic recombination occurs during
production of eggs and sperm in each generationthat divides these genetic blocks into subsets ofchromosomes. It is possible to identify the specificblock inherited from each parent and relate thoseblocks to blocks found in the grandparents. Likewise, one might even discern the blocks back to theFoundation Stock. Unfortunately, such a tool does
not yet exist for horses, but a similar commercial
application is used by people to identify the originof their ancestors. We anticipate horse breeders may
seek to use such a tool one day.
Today we can apply genomics to assess one of
the concerns of horse breeders, namely inbreeding.
As noted above, the establishment of breeds relieson the identification and use of Foundation Stock.
An unintended consequence of this is inbreeding
and the attendant risk of inbreeding depression andthe appearance of deleterious hereditary diseases.
The article in this issue, “Genomics and Inbreeding,” describes the concern and identifies ways inwhich genomics can be used to monitor inbreeding
and assist breed registries to anticipate problems.
CONTACT:
Ernest Bailey
ebailey@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

Equine Disease Quarterly Newsletter

5

available in the United States, they represent aneffective and non-invasive method for screening
individual donkeys and herd populations andwould undoubtedly further our understanding of
the epidemiology and transmission of besnoitiosis
in the United States.
There are no known effective treatments forequine besnoitiosis. Treatment with anti-protozoal
medications ponazuril, trimethoprim-sulfamethozazole, and nitazoxanide have not been effective.
The potential for natural recovery from besnoitiosis
and the long-term prognosis for infected animals

remains unknown. The author has followed several infected donkeys for the past 5 years, noneof which have spontaneously resolved. Althoughbesnoitiosis has not yet been reported in horses inNorth America, cases have been described in Africa, and the potential for similar infections in the
United States cannot be excluded as a possibility.

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

CONTACT:
Sally DeNotta, DVM, PhD, DACVIM
s.denotta@ufl.edu(352) 392-2229
College of Veterinary Medicine
University of Florida
Gainesville, Florida

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

JANUARY 2020
Volume 29, Number 1

C O M M E N TA RYT

KENTUCKY

Peripartum Death in MaresComplications associated with foaling are asignificant cause of morbidity and mortality
in both foals and mares. Even apparently normal
births can result in significant internal and external
injury to the mare. In extreme cases, these injuries
can be severe and result in death or require humane
euthanasia of the dam.
A review of diagnostic case submissions to the
University of Kentucky Veterinary Diagnostic
Laboratory was conducted to assess equine peripartum deaths during the 2017 and 2018 foaling
seasons. Mares that died secondary to foaling
complications or were humanely euthanized due
to significant parturition associated injury were
included.
During the two-year period, 121 cases of peripartum death were identified out of approximately
3,000 equine necropsy submissions. Cases werecategorized into five groups (gastrointestinal,
musculoskeletal, reproductive, vascular, and miscellaneous) based on the primary organ systemassociated with the cause of death. Submissions
began in December and extended into June ofboth years. Deaths occurred in multiple breeds,
but Thoroughbreds predominated.
Fatal lesions associated with the gastrointestinal tract were most common and occurred in 52(43%) cases. Diseases with the highest incidence
included cecal rupture (12%), colonic torsion(7%), colonic rupture (4%), rectal prolapse (3%),
cecal impaction (3%), gastric rupture (3%), rectal
tear (3%), and non-infectious inflammatory processes (3%). One to two cases of small intestinal

perforation, mesenteric rents and tears, and colonicdisplacement were also identified.
Fatal vascular lesions accounted for 24% of
peripartum deaths and included the No. 1 causeof death during the review period, rupture of theuterine artery. Ruptures of the uterine artery wereby far the most common vascular lesion (17%),frequently resulted in secondary hematoma formation in the broad ligament, a connective tissue
structure that supports the uterus, and hemoperitoneum. Infrequent ruptures were also associatedwith the internal iliac artery (3%), circumiliac
artery (1%), ovarian artery (1%), and aorta (1%).
Two cases of broad ligament hematoma were recorded, in which the exact location of the vascularrupture could not be determined.Direct injury to
the mare’s reproductive tract occurred in 22% of
the cases and frequently resulted in humane euthanasia. Uterine tear/rupture was most frequentin this category and occurred in 12% of the cases.
Less common reproductive injuries included uterine prolapse and vaginal lacerations, each of which
occurred in 3% of mares. Single cases of hydrops
pregnancy, uterine adhesions, uterine torsion, andsignificant vaginal hemorrhage were also noted.
Surprisingly, injuries to the musculoskeletal
system resulted in euthanasia of 10 (8%) mares.
Fractures (5%) were most common followed by individual cases of hip joint luxation, diaphragmatic
hernia, significant muscle trauma, and peripheral
nerve damage. Fractures were specifically associated with the pelvis, tibia, and femur and werenoted to occur in mares during dystocia events,

suffering post-foaling pain, and being transported
to a veterinary clinic.
The miscellaneous group included four sporadic
and individual cases that occurred in the peripartum time period. These cases included death or
euthanasia due to uncontrollable post-dystocia
pain, a presumed cardiovascular event following
dystocia, an anaphylactic drug reaction, and liverdisease of unknown cause.
Dystocia was specifically mentioned in theclinical history of 19% of the 121 cases. Although
the accuracy of this self-reported number is notdefinitive, it does emphasize that many injuries
during the foaling period are not associated withdifficult births.

In summary, equine death associated with thefoaling period is unfortunately common. The
underlying causes likely include a mixture of diseases associated with birthing trauma, pain, fetal
movement and positioning, and vascular changes
associated with gestation. Evaluation of mares during and following parturition is essential to rapidly
identify and treat this unique group of diseases.
CONTACT:
Dr. Alan Loynachanalan.loynachan@uky.edu(859)257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, Kentucky

he art of horse production is pattern recognition. The most obvious pattern is thatIN THIS ISSUE
offspring resemble their parents. These resemblances can be found in phenotypes such as size,
Commentary
conformation, durability, and performance. Using
phenotypes and pedigrees, breeders have applied
International
selection, resulting in profound changes in horses
Third Quarter2019  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2 since their domestication 5,500 years ago. Today,
hundreds of breed registries exist, reflecting diverse
Inbreeding and
Genomics .  .  .  .  .  .  .  .  .  .  . 3 goals among horse breeders. These interests spandivergent phenotypes related to racing, pulling,
National
jumping, dressage, performing special gaits, andBesnoitiosis incharacteristics associated with coat color or size.
Donkeys  .  .  .  .  .  .  .  .  .  .  .  . 4 The commonality among these traits is they havea large genetic component. Foundation Stock were
Kentucky
identified exemplifying traits of interest. The path
Peripartum Deathin Mares  .  .  .  .  .  .  .  .  .  .  .  . 5 to improvement has been to identify quality breeding stock, cross them to Foundation horses andselect the best for future breeding stock. As a result,Foundation Stock are represented many times inhorse pedigrees and contribute to the distinctive
phenotypic characteristics within those breeds.
Recently, a reference whole genome sequenceof the horse was determined. Scientists identified genes for discrete traits such as coat colors
and some hereditary diseases. However, despite
a great deal of research, no single gene has beenfound responsible for complex traits such as racing, jumping, and gait. This is not surprising sinceathletic performance involves a combination ofmuscle strength, cardiovascular capability, comCollege of Agriculture, petitiveness, and coordination. Yes, a few genes
Food and Environment
have been identified that influence performance
Department of(e.g., DMRT3 for gait and MSTN for sprintVeterinary Scienceing); however the development of champions
involves many other genes as well as the art of the
trainer and skill of the rider. This relationship isremarkably complex since variation exists despite
Lloyd’s—An international
generations of selection. The resilience of genetic
insurance market forvariation may reflect the diverse ways in which a
bloodstock and otherhorse can become a champion. Northern Dancer
specialist insurance.

and Secretariat were champion Thoroughbred
racehorses; however, while Northern Dancer was
relatively small in stature, Secretariat was renownedfor his large size and stride length. While the oldbreeding adage is “breed the best to the best andhope for the best,” the skill of the successful breeder
is to identify hereditary patterns among the best
and make judicious choices. There is no single
genetic test that will replace the skill of the breeder.
Genomic tools have the potential to improve therecognition of useful patterns. Horse genes are distributed among 32 pairs of chromosomes (see theimage in the online version of this issue at http://
gluck.ca.uky.edu/equine-disease-quarterly). Thesechromosomes contain the genetic material underselection. Genetic recombination occurs during
production of eggs and sperm in each generationthat divides these genetic blocks into subsets ofchromosomes. It is possible to identify the specificblock inherited from each parent and relate thoseblocks to blocks found in the grandparents. Likewise, one might even discern the blocks back to theFoundation Stock. Unfortunately, such a tool does
not yet exist for horses, but a similar commercial
application is used by people to identify the originof their ancestors. We anticipate horse breeders may
seek to use such a tool one day.
Today we can apply genomics to assess one of
the concerns of horse breeders, namely inbreeding.
As noted above, the establishment of breeds relieson the identification and use of Foundation Stock.
An unintended consequence of this is inbreeding
and the attendant risk of inbreeding depression andthe appearance of deleterious hereditary diseases.
The article in this issue, “Genomics and Inbreeding,” describes the concern and identifies ways inwhich genomics can be used to monitor inbreeding
and assist breed registries to anticipate problems.
CONTACT:
Ernest Bailey
ebailey@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky