(additional reading if desired: Goodwin, Current Vet Therapy 3 - Food
Animal Pract; Howard, ed.; p 787.)
- A certain number of abortions are expected to occur within a year.
A single isolated case may not warrant a full investigation.
However, in the face of continued losses or an abortion storm
investigation is indicated.
- A thorough, objective history should be taken along with a good
clinical exam. Laboratory investigation requires good material and a
good history to have a reasonable chance at arriving at a diagnosis.
The average success rate of arriving at a diagnosis for an abortion
is approx. 25%. To increase the chances of arriving at a diagnosis,
submit several fetuses and placentas. Paired serum samples, from
multiple animals, may be indicated if certain diseases are
- Numerous obstacles to diagnosis exist (see Kirkbride, Comp. Cont.
Ed, 1982 4:S341 for further reading). Abortion is often the result
of events occurring weeks to months previously and the cause, if it
was ever present in the fetus, is often undetectable by the time of
the abortion. The fetus is often retained in utero for hours to days
after death, resulting in autolysis which hides lesions. Fetal
membranes are often unavailable. Toxic and genetic factors are not
always discernible in available specimens. Many causes are unknown
and no diagnostic procedures are available.
- When an abortion occurs, in many cases the farmer finds the dead
fetus but may not know which cow it came from. To narrow down the
possibilities, it is helpful to know approximately how old the fetus
is. To estimate the age of a dead fetus refer to gestation estimates
based on size of the fetus.
- In other cases, it would be helpful to be able to estimate how
long a fetus has been dead (for example when correcting a dystocia
and delivering a dead calf).
- Estimation of the length of time a fetus has been dead in utero:
12 h - cloudy cornea; 24 h - kidneys soft and pulpy, abomasal
contents cloudy, mucoid, and flocculent; 36-96 h - subcutis
gelatinous and reddish or blood tinged; liver soft and friable;
abomasal contents reddish.
- Abortion - expulsion of dead conceptus or a living one incapable
of independent life;
- Premature delivery - preterm birth of immature viable fetus;
- Stillbirth - dead fetus expelled at term.
- Genetic : most genetic causes of abortion are "Beyond
routine diagnostic capabilities". The majority occur before
pregnancy is diagnosed, therefore go undetected (See "Repeat
Breeder" section). Numerous congenital defects have been
reported, some of which result in abortion.
- Nutrition : Nutrition is seldom a cause of abortion but
does result in dystocia and the birth of weak calves. Vitamin A
deficiency of long duration will result in abortion in a small
number of animals, weak calves, and increased incidence of retained
- Iodine deficiency and selenium deficiency have been
proposed to cause abortion.
- Environmental : High maternal body temperature results in
profound fetal hypotension, hypoxia and acidosis, but is usually due
to maternal illness rather than environmental temperatures. Stress
is often blamed for abortion but difficult to prove and has not been
documented as a cause. Keep in mind however, that abortion or
parturition can be induced with exogenous corticosteroids.
Inflammatory conditions can result in abortion if they are
associated with sufficient PGF release.
- Physical : Trauma is an unlikely cause of abortin,
especially in mid to late gestation. Trauma due to palpation of the
amniotic vesicle or fetal membranes in early gestation can result in
pregnancy loss if overly rough. Rupture of the amniotic vesicle or
trauma to the large vessels leading to the fetal heart can result in
death of the conceptus. Remember that the fetal heart sac is outside
of the body until the 6th week in the bovine.
- Nitrate : Reports of abortion due to nitrates exist in the
literature from the late 1950's. In general, a causative effect is
questionable, with proof lacking. Feeding a high level of NO3 failed
to cause abortion in one study, however, theoretically nitrates
could affect the fetus by reducing oxygen availability. It has been
suggested that nitrates in conjunction with certain plants may play
a role in some abortions.
- Sodium iodide (i.v.): Its use during pregnancy has been
avoided because of the threat of abortion. However, this has not
been proven experimentally.
- Corticosteroids can cause unwanted pregnancy loss, usually
through inadvertent administration to pregnant cows.
- Pine needle abortion: Pine needles from the Ponderosa Pine
( Pinus ponderosa) contains an anti-estrogenic compound.
Ingestion of the needles results in abortion during the last
trimester. Cows develop an addiction in favor of the pine needles
over good feed. A high protein diet increases the risk of abortion.
Abortion is characterized by a hemorrhagic condition of the placenta
and fetus. Incomplete dilation of the cervix, retained placenta and
metritis are common. Prevention requires physically isolating the
cows from the pine needles to decrease losses. Pine needles are
dangerous whether fresh, dry, fallen, on the tree, etc. The pine
needles do not cause abortion in sheep but may increase the rate of
dead lambs at parturition.
- Oxytropis and Astragalis sp. cause
abortion. The toxic principle is an indolizidine alkaloid, causing
abortion if cows ingest large amounts or fetal abnormalities with
- Verratrum californicum - It is associated with the
cyclops condition in sheep.
- Moldy sweet clover causes abortion, the causative agent is
- Other plants for example, perennial broomweed and Locoweed are
known to cause abortion.
- Infectious Bovine Rhinotracheitis ( IBR ) The causative
agent is bovine herpesvirus 1. The virus can remain viable for years
when frozen. It causes a variety of clinical syndromes, such as
necrotic rhinitis or "red nose" (covered in other
courses), conjunctivitis, CNS infection, neonatal infection and
coital vesicular exanthema. Coital vesicular exanthema is commonly
called infectious pustular vulvovaginitis (IPV) in the cow and
infectious pustular balanoposthitis (IPB) in the bull. The disease
may be mild and unnoticed or may be very painful as evidenced by
tail swishing, raised tail, frequent urination and an edematous
hyperemic vulva. The mucosa will be covered with small pustules
which coalesce to form white necrotic plaques that leave ulcers (on
vulva or on penis/prepuce). Mucopurulent exudate may be seen.
Lesions heal in 10-14 d. Genital forms of IBR are spread in
secretions of reproductive organs. Latent infections are common. The
virus may persist for years (trigeminal ganglia) in the animal. It
can be reactivated by a corticosteroid injection resulting in active
shedding. It ahs been suggested that stress can stimulate endogenous
corticosteroid release and similarly result in active shedding.
Abortion can occur after inapparent infection or after respiratory
disease, conjunctivitis, IPV. Abortion usually occurs during the
last trimester. The time from infection to abortion is variable.
Occasionally the fetus is carried to term and dies shortly after
delivery. Usually, however, the fetus is autolyzed (unlike in the
mare). Diagnostic lesions are focal necrosis and intranuclear
inclusions in the liver and adrenals. There are no characteristic
gross lesions. Paired maternal sera are of little value because of
the ubiquitous nature of the virus, widespread vaccination and most
importantly because of the time lapse between maternal infection and
abortion. Prevention is best accomplished with a good vaccination
program. Caution must be exercised with Modified Live Vaccines
because they can result in abortion and temporary necrotic
oophoritis (especially of the CL). In general, killed vaccines are
safe to use in pregnant cows. It is best to follow the
manufacturer's directions. Heifers should be vaccinated after 5
months of age. Vaccinate heifers at least 1 month before breeding.
Double sheathing the AI pipette has been suggested to reduce the
risk of transferring virus from the vagina/vulva into the uterus.
- M. bovis; generally associated with infertility (see
- M. bovigenitalium occasionally causes abortion.
- Ureaplasma sp. also ocasionally causes abortion, usually in
the last trimester. Placentitis and fetal pneumonitis are common.
- Salmonella (usually S. dublin, ocasionally other
serovars) may cause abortion.
- Haemophilus somnus: occasionally causes abortion with
retained placenta at 7-9 months of gestation. Listeriosis (Circling
Disease, Silage Sickness) is caused by L. monocytogenes.
The normal habitat of this bacteria is soil and the intestinal
tract. Infection is usually by the fecal - oral route. Poor quality
or poorly cured silage (pH>5.6) provides a favorable
substrate for the organism. The majority of infections are
asymptomatic. The organism has a predilection to localize in the
intestinal tract, placenta and medulla oblongata. Uterine contents
quickly become infected. Sporadic abortion is observed at any stage
of gestation but usually in the last trimester. When abortion occurs
near term, the calf may be stillborn, born alive and die shortly
after birth or survive. There are typically no premonitory signs of
abortion. In cases of abortion, no clinical signs are observed in
the dam. Usually the dam recovers spontaneously. Fetuses are
slightly to markedly autolyzed. The fetus has excess clear to blood
tinged fluid in its serous cavities. Small necrotic foci are found
in the liver, lungs and spleen. A Gram stain of abomasal contents
may reveal the organisms. Diagnosis is made by isolation and
identification of the organism, fluorescent antibody techniques or
direct stained smears. Control is accomplished by improving hygiene
and avoiding feeding spoiled silage.
- Mycotic : Fungi are estimated to be the cause of 2 to 30%
of all infectious abortions. Two-thirds of mycotic abortions are due
to Aspergillus fumigatus. Other species of fungus
implicated in bovine abortion include Mucor, Rhizopus,
Absidia and Mortierella. The source of infection is
usually external via the respiratory or GI route. Alternatively, it
may be from genital / vaginal flora or contaminated semen. Abortions
may occur anytime after the 3rd month of gestation but are most
common in late pregnancy. Mycotic abortions tend to peak during the
winter. Pathogenesis is usually the result of a generalized
infection with blood borne dissemination and subsequent localization
in the placenta resulting in placentitis, necrosis, and hemorrhage
with separation of the chorion from the caruncle by exudate. There
are usually on clinical signs in the dam and the fetus may be
grossly normal as well. Some fetuses (2-25%) may have ringworm -
like skin lesions in which fungal elements can be demonstrated
(especially in the head and neck region). Fetal lesions include
generalized lymphadenitis, dehydration and emaciation. Necrotizing
hemorrhagic placentitis with retained placenta is common.
Microscopic lesions include vasculitis, bronchopneumonia, and
necrotizing epidermitis. Diagnosis is made by demonstration of fungi
in association with significant lesions. Tissues to submit include
placenta, especially cotyledons; kin lesions, lymph nodes, lung and
stomach (with contents).
- Chlamydia : Chlamydia are obligate intracellular bacteria.
They are susceptible to tetracylines. Abortions occur without
clinical signs as early as 5 months of gestation but usually occur
in the last trimester. Retained placentas are common. Abortions are
usually sporadic. The route of infection is hypothesized to be via
ingestion of tissues but may involve birds as carriers. Rebreeding
problems are common after abortion. Placentitis is a consistent
lesion, while fetal lesions vary considerably. Diagnosis requires
laboratory confirmation. Intracytoplasmic inclusions are
characteristic. Paired sera are helpful in suspected cases. No
vaccine is available, therefore prevention centers on hygiene while
prevention of further cases is usually based on tetracyclines in the
- Parvovirus : Typically, no clinical signs are observed in
the dam. Abortions are most common in the 1st half of gestation. The
fetus and placentas are edematous and the cotyledons necrotic.
Diagnosis is by hemagglutination inhibition test.
- Epizootic Bovine Abortion commonly known as Foothill
Abortion is a vector transmitted disease. The etiologic agent is
unknown. The vector is the argasid tick, Ornithodoros coriaceus.
Last trimester abortions are seen. The disease occurs annually in
certain areas of California. Abortions are characterized by a sudden
onset with high fetal mortality. The disease is confined to 1st calf
heifers (females in their first pregnancy). There are no clinical
signs in the dam. The fetus is delivered in a fresh state.
Hemorrhages are observed on the ventral surface of the tongue. Straw
colored peritoneal and pleural effusions are common. The
subcutaneous tissues are often edematous. The liver is swollen and
nodular, the spleen enlarged, and the lymph nodes enlarged and
edematous. Prevention is accomplished by exposing yearlings and open
2 year-olds to summertime brush areas where the tick lives, and
breeding in the fall.
- BVD: The etiologic agent is a Pestivirus in the family
Togaviridae. It is related to hog cholera in swine, border disease
in sheep and equine arteritis virus (EAV). It is found worldwide.
The virus can infect many species. The virus is shed in feces and
nasopharyngeal secretions. It is transmitted by aerosol droplets and
by the oral route from fecal contamination (which is the most
probable route). Vector and mechanical transmission are also
possible and vertical transmission is common. The majority of
infections are unapparent, subclinical and lack clinical signs. When
present, a variety of clinical signs may be observed and may be
acute, chronic (cattle are considered "poor doers") or
mild clinical. Clinical signs include immunosuppression (see Food
Animal notes). Reproductive effects are variable. Associated with
significant reproductive losses (fertilization failure, early
embryonic death and abortion). Congenital malformations, especially
of the CNS, may be seen as well. Determining factor of the outcome
is the age of the fetus at the time of infection. Abortion is more
likely if infection occurs in the early months of gestation. Fetal
expulsion can occur close to the time of maternal infection or many
months later. Congenital abnormalities may be observed. Affected
fetuses may be aborted or carried to term. Most common congenital
defects include cerebellar hypoplasia, ocular dysgenesis (microphthalmia,
congenital cataracts), brachygnathia and musculoskeletal defects.
Fetal mummification may be observed. Diagnosis is by virus
isolation, identification of viral antigens by immunofluorescence or
enzyme immunoassay. Demonstration of rising antibody titers are less
useful in abortion cases. There is a relatively high incidence of
BVD infection in fetuses so isolation of virus or demonstration of
BVD antibodies in the serum from the fetus may not necessarily be
diagnostic. BVD should not be considered the cause of abortion
unless BVD lesions are present or cases of BVD have occurred in the
herd. Prevention is accomplished by vaccination. Caution should be
used with modified live vaccines as they can cause abortion. Killed
vaccines are available. Annual booster vaccination is required with
killed vaccines. Calves should be vaccinated after 6-8 months of age
when maternal antibodies have passed. Persistent carriers may occur
after fetal infection in utero before the immune system has matured.
The virus is not recognized as foreign and is shed by that
individual after birth. Because of the problem posed by persistent
carriers, one form of control advocated by some is to vaccinate and
then check titers. Any cattle not developing a titer should be
culled, because they failed to recognize the vaccine as foreign and
develop antibodies. These individuals are most likely persistent
- Leptospirosis: The etiologic agent is a spirochete, Leptospira
interrogans, which has over 180 serovars in 19 serogroups. Each
serovar is adapted to a particular reservoir host but can cause
disease in any mammalian species (Table 28). The reservoir host has
a high susceptibility to infection and endemic transmission.
Pathogenicity in the reservoir host is relatively low, with a
tendency to cause chronic rather than acute disease. However,
insidious economic loss occurs through reproductive losses.
Persistence in the kidneys and/or the genital tract may occur. In
the reservoir host, the antibody response, as determined by the
micro-agglutination titer (MAT) is low. In contrast, in an
incidental host there is relatively low susceptibility with sporadic
transmission. However, pathogenicity is high, characterized by
acute, severe disease. There is a short kidney phase and a marked Ab
response. Transmission can be direct, such as through urine
splashing, placental and uterine discharges after an abortion,
through the milk, transplacentally or venereally. Transmission can
also be indirect, by environmental contamination of feed by urine of
carrier animals. Survival of the leptospire is favored by moisture,
moderately warm temperature and neutral to mild alkaline pH. The
organisms may survive weeks to months under good conditions, yet
only minutes if conditions are dry or <10oC or >34oC.
Pathogenesis: Leptospires penetrate mucous membranes and
water-softened skin. After a 4 to 10d incubation period, they
disseminate to many organs in a leptospiremic phase lasting up to
7d. During this period, acute clinical disease may be seen. Antibody
production, which is detectable about 6d after the leptospiremia
begins, stops the bacteremia and allows the leptospires to persist
only in tissues of poor antibody penetration, resulting in chronic
infection. Leptospires can persist in the kidneys and be shed in the
urine for several weeks in an incidental host, or 6 months or more
in a maintenance host. Leptospires can also persist in the genital
tract of a maintenance host. For example, hardjo in cattle - oviduct
(3wks), uterus (3-5 mos.), testes, seminal vesicles, prostate. In
cattle, the major serovars are hardjo and pomona (type kennewicki).
Acute disease is most commonly manifested as mastitis in dairy cows.
Chronic infection is manifested as abortion, stillbirth, and the
birth of premature and weak infected calves. Retained fetal
membranes are common after hardjo abortion. Abortion may be the only
manifestation of infection or may be related to an episode of
illness 6 (pomona) or 12 (hardjo) weeks earlier. Hardjo infection is
associated with infertility (early embryonic death (EED)) and
abortion (4 months to term), while pomona infection is associated
with abortion during the last trimester. Signs in the aborted fetus
are negligible. Focal tubular necrosis and interstitial nephritis
may be seen. Autolysis of the fetus is common. Diagnosis: Darkfield
microscopy and silver staining of tissues are insensitive methods.
Immunofluorescence of urine or homogenates of fetal lung and kidney
or of the placenta is a good technique. When obtaining specimens for
submission, it is important to remember that leptospires die rapidly
in tissues unless kept at 4oC. The presence of leptospires in urine
from cows that have recently aborted does not distinguish these cows
from renal carriers. Serologic diagnosis is by Microscopic Agglutination
Titer (MAT). This technique is useful in the diagnosis of the
incidental host, but is less useful for diagnosis of the maintenance
host. Herd serologic response is more helpful. Testing of fetal
fluids in abortions is useful. A titer >100 is significant
(>10 in fetal fluids). Paired sera are of no use in
chronic infection, but are useful in acute infection. To test the
herd, sample 10 animals from each management or age group. Titers >300
for hardjo indicate active infection. For treatment of acute
infection administer tetracycline. Control is achieved through
hygiene and vaccination.
- Limit transmission by carriers. Reduce
contact with wildlife, control rodents, especially contamination of
feed. Fence swampy ground. Vaccination is recommended. Immunity is
short lived, therefore vaccinate twice a year in open herds.
Vaccines vary in efficacy and vaccine failures may occur. The
vaccine is inexpensive and safe to use iin pregnant cattle.
- Neosporosis : This was first identified as a cause of
abortion in 1989. The etiologic agent is a protozoa of the genus Neospora.
The species is unclear. The life cycle is unknown but is probably
similar to Toxoplasma gondii (i.e. oral route of infection
with transplacental infection of the fetus; carnivore sheds oocysts
in feces; oocysts are ingested by cattle, sheep and goats; carnivore
eats cattle, etc). Abortion occurs at 3 to 8 (usually 5 to 6) months
of gestation. Gross lesions are non-specific and the fetus is
usually autolyzed. There is usually no metritis or retained fetal
membranes after abortion. Occasionally the calf is born alive with
hindlimb weakness or paralysis, but this carries a poor prognosis.
However, congenital infection is not necessarily detrimental to the
calf's health. Congenital transmission consitutes a major mode of
transmission. There is no known treatment for the disease.
Prevention is accomplished by protecting the feed and water from
fecal contamination and fecal contact. On necropsy, an\borted
fetuses have multifocal, necrotic, non-suppurative encephalitis
along with mononuclear myositis and myocarditis. An
immunohistochemical stain is used to identify the organism in tissue
sections. Ttissues not fixed in neutral buffered formalin may result
in false negatives. An Indirect Fluorescent Antibody test (for N.
caninum) is also used. This disease may be a leading cause of bovine
abortion. The significance of iImmunity after abortion is unknown.
Some cows abort repeatedly but it is unknown if it is due to a
chronic latent infection or recovery and reinfection. Some cows give
birth to affected calves in subsequent pregnancies.
- Brucellosis : The species affecting food animals are: Brucella
abortus Y cattle, elk, bison; B.
melitensis Y goats and sheep; B.
suis Y swine and reindeer.
Transmission is by the oral route (B. Abortus and B. melitensis);
oral and genital route (B. suis in swine); and oral route (B.
suis in reindeer). Infection begins when the organism breaches
the mucosal epithelium and makes its way to the local lymph node.
This is followed by a bacteremia of variable duration. The
incubation period can be as short as two weeks to as long as one or
two years. The organism resides in the distal lymph nodes, spleen,
bone marrow, joints, CNS, mammary gland, testicle, epididymis,
seminal vesicles, prostate, and pregnant uterus. Clinical symptoms
include abortion or birth of near-term weak offspring in cattle,
acute to subacute mastitis in goats and sheep, chronic mastitis in
cattle, orchitis and epididymitis in males. The social
characteristics of cattle, herd females helping with the clean up
following a birth, is an important epidemiological factor to
remember when considering that primary exposure follows abortions,
because the placenta and reproductive tract discharges are rich
sources of the organism.
- Susceptibility varies with 18-20% of the
population being very resistant. There is an age and sex related
susceptibility with males less susceptible than females and sexually
immature females less susceptible than mature females. Pregnant
females are the most susceptible. Most infected cows abort only
once. Brucellosis is generally considered a first calf heifer
disease in a chronically infected herd. Vertical transmission is
rare and results in latently infected heifers. The organisms may be
frequently shed in milk resulting human infection (undulant fever).
Various diagnostic methods may be employed. The most common are
serological tests, either on farm, at the market, or at slaughter.
In a dairy herd, a milk ring test is performed every 3 months on a
milk sample from the bulk tank. If results are positive, the milk is
retested by heat inactivation. If results are still positive the
area regulatory veterinarian is contacted. They can get a second
milk sample and retest. If results are positive, then the entire
herd is tested by serological means. As an option, they may decide
to just test the entire herd without rechecking the milk. Individual
animals are tested using a Buffered Acidified Plate Antigen (BAPA)
or card test. Sometimes a rivanol test is used. The final test is a
Complement Fixation Test. At market, a card test is performed,
followed by a CITE if positive. If both testa are positive the
animal is considered a reactor. If the card test is positive and the
CITE negative, the owner can either take the animal home and retest
it later (which is the preferred option) or brand the animal with an
"S" (suspect). The disease may also be diagnosed on the
basis of a diagnostic laboratory abortion screen, culture or
pathology. Brucellosis has zoonotic potential causing Malta fever,
undulant fever, or spring fever. It is shed in the milk (therefore
raw, or unpasteurized, milk is prohibited in most states), but meat
from infected animals is safe. Symptoms are highly variable. Because
of its zoonotic potential, regulatory aspects have been instituted.
Limited movement of animals from infected herds and from states with
infected herds is allowed. Vaccination programs are regulated,
stating which vaccines are allowed and the time frame during which
they may be used. Brucellosis vaccination alone will not eliminate
the disease. Only live vaccines are used. To be effective,
vaccination must mimic a natural infection and the bacteria must
remain alive in the host's tissues for at least 7 days. Immunity is
due to cell mediated immunity. Remember that antibodies are not
protective in ruminants and swine. Living vaccines that are or have
been recently available include Rev 1 for B. melitensis, and
Strain 2 for B. suis. Strain 19 was used in the past for B.
abortus but has been replaced with Strain RB51. One problem with
the live vaccines (especially Strain 19) is that they may cause post
vaccine titers which interfere with diagnostic tests. This problem
is greatly reduced with Strain RB51. RB51 may be effective in all
animals including wildlife. The live vaccines may infect animals
resulting in abortions and arthritis. They cannot be used in males
because they can cause reproductive tract infections and sterility.
The vaccines are infectious to man.
contributed by Bruce
E Eilts, and
modified 14 September 2004
assisted by Eric Huey and Emma Jones