Abortion in Cattle

Bluetongue is caused by an orbivirus and is transmitted mainly by biting midges of the genus Culicoides. Transplacental transmission is one of the major causes of reproductive losses, including abortion, stillbirths, and fetal mummification, in cattle and sheep.

Multiple bluetongue virus serotypes have been identified; currently, BTV-3 is the most commonly isolated serotype in Europe. Regardless of the serotype, bluetongue virus causes abortions, stillbirths, and congenital CNS malformations (eg, hydranencephaly) in calves.

Diagnosis: Diagnosis of bluetongue is based on identification of precolostral antibodies against bluetongue virus or identification of the virus by PCR assay. Brain, spleen, and whole blood are the preferred samples from fetuses and neonates for PCR assay.

Prevention: Bluetongue in cattle is controlled by vaccination and management procedures to decrease exposure to biting midges. Modified live and inactivated vaccines are available; however, their availability and use vary by country.

Bovine viral diarrhea virus (BVDV) is consistently among the most commonly diagnosed viral agents in bovine abortion cases and has been identified in several surveys as an important cause of bovine fetal loss (1). BVDV is a pestivirus closely related to border disease virus. Despite the overall low prevalence of BVDV, herds occasionally harbor persistently infected animals.

The pathogenesis of BVDV infection in the developing fetus is complex and highly dependent on the stage of gestation at the time of infection. Infection before insemination or during the first 40 days of pregnancy typically results in embryonic death and subsequent infertility. Infection between 40 and 125 days of gestation can lead to the birth of a persistently infected calf.

Fetal infection with BVDV during organogenesis (at approximately 100–150 days of gestation) can result in congenital abnormalities of the CNS, including cerebellar hypoplasia, hydranencephaly, hydrocephalus, microencephaly, and spinal cord hypoplasia, as well as ocular defects such as cataracts, optic neuritis, retinal degeneration, and microphthalmia. In some cases, infection during this period can also result in abortion, or the fetal immune system might clear the virus.

Diagnosis: Diagnosis of bovine viral diarrhea is based on identification of the virus by means of isolation, immunological staining, PCR assay, or detection of precolostral antibodies against BVDV in aborted calves. The virus is present in a wide variety of tissues, but the spleen is the tissue of choice for testing. Increasing BVDV antibody titers in aborting animals or herdmates is diagnostic for recent infection.

BVDV is immunosuppressive and is found in many fetuses with infections caused by other agents (eg, bacteria, the protozoon Neospora caninum). Outbreaks of abortions due to organisms that typically cause sporadic abortion should raise suspicion for possible concurrent BVDV infection.

Prevention: Measures to prevent bovine viral diarrhea in cows should focus on removal of persistently infected cattle and herd vaccination.

Brucellosis in cattle is caused by Brucella abortus, a gram-positive, facultative intracellular bacterium with tropism for the reproductive tract, where it causes placentitis, late-term abortion, and infertility. B abortus infects males as well, causing orchitis, epididymitis, and potential sterility.

In the US, active control programs, including test-and-cull and heifer vaccination, led to the eradication of brucellosis in domestic cattle. However, the disease persists in bison and elk populations.

Diagnosis: Maternal serological testing, combined with fluorescent antibody staining of the placenta and fetus or isolation of B abortus from the placenta, fetus (abomasal contents and lung), or uterine discharge, is the method suggested for diagnosis of brucellosis.

Grossly, the placenta of a fetus infected with B abortus shows necrotic cotyledons that can be red or yellow. The intercotyledonary area is focally thickened and has a wet, leathery appearance. The fetus can be normal or autolytic, with bronchopneumonia.

Prevention: In 2023, 69 years after initiation of the US brucellosis eradication program, the USDA declared the disease eradicated from domestic cattle. It is now considered a wildlife disease. Some states (such as Oregon) have removed mandatory vaccination; Washington, Idaho, Wyoming, Montana, and Utah still require it.

The standard vaccine is B abortus strain RB51, typically administered to female heifers 4–12 months old. Vaccinated animals receive an orange ear tag and an ear tattoo on the right side. B abortus is zoonotic, and it is still a reportable disease, so the appropriate authorities should be contacted.

In cattle, campylobacteriosis (also known as vibriosis) is caused by Campylobacter bacteria. Campylobacter fetus venerealis (see C fetus venerealis image) causes venereal disease that usually results in infertility or early embryonic death but occasionally causes abortion between 4 and 8 months of gestation.

Campylobacter fetus venerealis, bovine abortion, photomicrog...

Image

Photomicrograph showing Campylobacter fetus venerealis, cultured after bovine abortion. Dark-field microscopy.

Courtesy of Dr. J. Glenn Songer.

Campylobacter fetus fetus and Campylobacter jejuni are transmitted to bovine fetuses by ingestion and subsequent hematogenous spread to the placenta. Both of these bacteria cause sporadic abortions, usually in the second half of gestation. The fetus can be fresh with partially expanded lungs, or it can be severely autolyzed. Mild fibrinous pleuritis and peritonitis, as well as bronchopneumonia, might be present. Placentitis is mild, with hemorrhagic cotyledons and an edematous intercotyledonary area.

Diagnosis:Campylobacter spp can be identified by dark-field examination of abomasal contents or by culture of the placenta or abomasal contents. Isolation and identification of the species involved are important if vaccination is to be instituted.

Venereal campylobacteriosis can be controlled by artificial insemination and vaccination. Campylobacter spp are zoonotic, and C jejuni is an important cause of enteritis in humans. (Also see Bovine Genital Campylobacteriosis.)

Prevention: Vaccination against the venereal disease caused by Campylobacter fetus is recommended for breeding cows and heifers. An annual dose before breeding is suggested to decrease transmission. Two doses 4 weeks apart are administered as initial vaccination.

Vaccination of bulls has been recommended in herds with substantial exposure to C fetus venerealis. Experimental studies have also reported clearance of infection after vaccination of infected bulls; however, subsequent studies have demonstrated inconsistent therapeutic efficacy (5, 6, 7).

Chlamydia abortus, the cause of enzootic abortion of ewes, also causes sporadic abortion in cattle. Most bovine abortions occur near the end of the last trimester, but they can occur earlier. Placental lesions consist of thickening and yellow-brown exudate adhered to the cotyledons and intercotyledonary areas. Histologically, placentitis is consistently present, and pneumonia and hepatitis occur in some fetuses.

Diagnosis:C abortus can be identified by examination of stained smears of the placenta or by ELISA, fluorescent antibody staining, PCR assay, or isolation in embryonated chicken eggs or cell culture. Organisms can often be identified in the lungs and liver, but not as consistently as in the placenta.

Prevention: There are no vaccines against C abortus for cattle; however, C abortus vaccines are produced for sheep. The bacterium is zoonotic, occasionally producing life-threatening disease and abortion in pregnant women.

Epizootic bovine abortion (EBA) is a tickborne bacterial infection of cattle in the foothill region surrounding the Sacramento/San Joaquin Valley and the eastern Sierra Nevada range of California, Oregon, and Nevada.

EBA usually manifests as a protracted abortion storm that affects primarily heifers or cows recently introduced to a particular geographical region; however, abortion can occur in infected cattle 3–5 months after they have been removed from the endemic area. Abortion occurs usually in the last trimester, and rates can be as high as 60% (8). The animals abort without illness, and the fetus is seldom autolyzed.

EBA is caused by Pajaroellobacter abortibovis, a bacterium transmitted via the bite of the soft-bodied pajaroello tick (Ornithodoros coriaceus) found in the Sierra Nevada foothills. The aborted fetus can have hepatomegaly, splenomegaly, and generalized lymphomegaly. Microscopically, there is marked lymphoid hyperplasia in the spleen and lymph nodes, and granulomatous inflammation in most organs. Fetal IgG is increased.

Cows that abort as a result of P abortibovis infection seldom abort in subsequent pregnancies, and heifers are often intentionally exposed to endemic areas before breeding age in an effort to prevent abortions.

Diagnosis: The geographical location and the presence of O coriaceus ticks in the area, together with typical EBA lesions of the fetus (thymic atrophy and lymphoid hyperplasia), help confirm the diagnosis of P abortibovis infection.

Prevention: Exposing heifers to EBA-endemic areas before breeding helps to build their immunity to P abortibovis infection.

Infectious bovine rhinotracheitis (IBR), caused by bovine alphaherpesvirus 1 (BoHV-1), is a major cause of viral abortion in cattle worldwide. Although IBR has been eradicated or is under eradication programs in several European countries, it remains endemic in North America and is an important cause of abortion, with reported abortion rates of 5–60% in unvaccinated herds. BoHV-1 also causes infectious pustular vulvovaginitis (IPV) (9).

IBR virus is a herpesvirus, and like all other herpesviruses, it causes latent infections. Infected animals remain carriers for life. IBR virus reaches the placenta in white blood cells and, over a period of 2 weeks to 4 months, causes placentitis and fetal death.

Abortion caused by IBR typically occurs after the initial respiratory disease, 4–7 months into gestation. Direct infection by the virus leads to autolysis of the fetus. Occasionally, small foci of necrosis can be found in the fetal liver; in most cases, however, there are no gross lesions on the placenta or fetus. Microscopically, necrosis with minimal inflammation is consistently present in the liver. Necrotizing vasculitis is common on the placenta.

Diagnosis: Diagnosis of IBR can be confirmed by immunohistochemical or immunofluorescent detection of IBR virus antigen in fetal tissues, particularly the kidney, lung, liver, adrenal glands, and placenta (10).

IBR virus isolation is most successful from the placenta; however, it can be unsuccessful in autolyzed fetuses. Historically, isolation has been reported in approximately one-third to one-half of infected fetuses (11).

PCR assay provides a sensitive and rapid alternative for detecting BHV-1 in fetal and placental tissues (12). In most cases, maternal titers have peaked by the time of abortion. In abortion storms, rising titers can often be demonstrated in herdmates.

Prevention: Several vaccines against IBR are available. Vaccination of whole herds every 6 months is recommended in endemic areas. The use of modified live vaccines against IBR should be avoided in pregnant or lactating cows because they can cause abortion. The use of glycoprotein E–deleted marker vaccines is considered the best option because it enables the differentiation of infected versus vaccinated animals.

Leptospirosis is a zoonotic disease caused by Leptospira bacteria. It is spread via the urine of infected animals. Leptospira serovars of major importance in cows are Hardjo and Pomona in North America, South America, Australia, and New Zealand; and Hardjo in Europe.

Two serologically indistinguishable but genetically distinct types of serovar Hardjo have been identified:

• Leptospira interrogans serovar Hardjo (type hardjo-prajitno) is isolated primarily from cattle in the UK.

• Leptospira borgpetersenii serovar Hardjo (type hardjo-bovis) (see L borgpetersenii image) is common in cattle populations throughout the world.

Leptospira borgpetersenii serovar Hardjo, bovine abortion, p...

Image

Photomicrograph showing Leptospira borgpetersenii serovar Hardjo, cultured after bovine abortion. Fluorescent antibody stain.

Courtesy of Dr. J. Glenn Songer.

Clinical signs of leptospirosis vary by bacterial serovar and host. In cattle, which commonly serve as maintenance hosts for certain Leptospira serovars, infection is often subclinical but can result in prolonged renal colonization and urinary shedding, enabling chronically infected animals to act as important sources of environmental contamination and transmission. Maintenance hosts show mild disease and prolonged renal carriage (13); incidental hosts often develop severe illness with high antibody titers and minimal carrier states. Young animals are generally more affected than older animals.

Many leptospiral infections are subclinical in cows; however, acute disease can cause fever, anemia, jaundice, decreased milk production, and agalactia, whereas chronic infection, especially with serovar Hardjo, is associated mainly with reproductive losses such as abortion, stillbirth, and infertility. In dairy cattle, the Hardjo serovar commonly causes transient decreases in milk production and chronic reproductive problems, whereas severe acute disease is more typical of incidental L interrogans serovars such as Pomona.

Although dams might show clinical signs of leptospirosis, most Leptospira-induced abortions occur in otherwise healthy cattle. Abortion rates vary from 5% to ≥ 40% (14).

Diagnosis: In cattle, leptospires cause diffuse placentitis with avascular, light tan cotyledons and edematous, yellowish intercotyledonary areas. The fetus usually dies 1–2 days before expulsion and therefore is autolyzed. Occasionally, calves are born alive but weak.

Bovine fetuses infected with Leptospira serovar Pomona might show icterus. There are no specific lesions; however, the placenta and fetus should be submitted to a laboratory for fluorescent antibody staining or PCR testing for Leptospira.

Although maternal Leptospira antibody titers are probably waning by the time of abortion, an initial titer of > 1:800 could be suspicious. Approximately one-third of cows that abort because of serovar Hardjo have titers of < 1:100 at the time of abortion (15).

Cows infected with serovar Hardjo can shed the organism in urine throughout life. For other serovars, the dam’s urine can be cultured or examined for leptospires within 2 weeks after abortion.

Prevention: To control Leptospira infections in cattle, infection sources (such as feed or water contaminated by dogs, rats, or wildlife) should be identified and eliminated. There is very little or no cross-protection among serovars.

Immunization against leptospirosis is based on the use of multivalent vaccines. Heifers should be vaccinated before breeding, with two doses administered 4–6 weeks apart, followed by an annual booster.

Treatment: Oxytetracycline, tilmicosin, ceftiofur, or amoxicillin may be used to decrease the clinical signs of Leptospira infection and stop the shedding of bacteria in the urine. The dosages for some of these medications are extralabel.

The bacterium Listeria monocytogenes can cause placentitis and fetal septicemia in cattle. Abortions are usually sporadic; however, outbreaks can occur, and abortion rates within affected groups can reach approximately 15% (16, 17). Abortion occurs at any stage of gestation, and the dam might show fever and anorexia before the abortion; retained placenta is common.

Fetuses that abort because of L monocytogenes infection are retained for 2–3 days after death, so autolysis can be extensive. Fibrinous polyserositis and white necrotic foci in the liver and/or cotyledons are common.

Diagnosis: Diagnosis of listeriosis in cases of bovine abortion is based on culture of Listeria from the fetus or placenta.

Prevention: There is no available bacterin against L monocytogenes.

Listeriosis is a reportable disease in many areas and is a serious zoonosis, with transmission to humans possible through improperly pasteurized milk.

Fungal placentitis that is due to Aspergillus spp (septated fungi, 60–80% of cases) or to Mucor spp, Absidia spp, Rhizopus spp, or any of a few other nonseptated fungi is an important cause of sporadic bovine abortion. Abortions occur from 4 months of gestation to term and are most common in winter.

The abortion-causing fungi that infect cattle are believed to gain entry through the oral or respiratory tract and to travel hematogenously to the placenta. Placentitis is severe and necrotizing. Cotyledons are enlarged and necrotic, with turned-in margins. The intercotyledonary area is thickened and leathery. Adventitious placentation is common.

Bovine fetuses aborted because of fungal agents are seldom autolyzed, but they might be dehydrated. Approximately 25% of these fetuses have gray, ringwormlike skin lesions that involve principally the head and shoulders (18).

Diagnosis: Diagnosis of mycotic abortion in cattle is based on the presence of fungal hyphae associated with necrotizing placentitis, dermatitis, or pneumonia. Fungi can also be isolated from the fetal gastric contents, placenta, and skin lesions. Isolation of the fungus must be correlated with microscopic and gross lesions to rule out contamination after abortion.

Prevention: To prevent mycotic abortion in cattle, moldy feed should be avoided.

Also see Mycotoxicoses.

Neospora caninum is a major protozoal cause of abortion in dairy and beef cattle worldwide.

Dogs and coyotes are definitive hosts for N caninum and can be the source of infection. Abortion can occur anytime after 3 months of gestation; however, it is most common between 4 and 6 months of gestation. Neospora can be associated with sporadic abortions or abortion storms, and repeated abortions in cows have been reported.

Most in utero N caninum infections are subclinical, but some infected calves are born with paralysis or proprioceptive deficits. Infected cows are not clinically ill, and placental retention is rare. The fetus is autolyzed (usually) or mummified (occasionally); rarely does it have gross lesions.

Diagnosis: Microscopically, nonsuppurative inflammation is common in the brain, heart, and skeletal muscles of cows infected with N caninum (see Neosporosis in Cattle). Organisms can be identified in these tissues and the kidneys by means of immunohistochemical staining and PCR assay.

Many late-gestation calf fetuses have detectable precolostral antibodies against N caninum. These calves remain infected for years and possibly for life. Vertical transmission is common.

Prevention: Strict hygiene to prevent the transmission of N caninum through fecal contamination of feed by dogs or coyotes is the best method for prevention of neosporosis in cattle.

There is no effective, widely available vaccine against N caninum. The main hurdle in developing a protective vaccine is the intracellular nature of the parasite and the need to prevent vertical transmission.

Infection by the protozoon Tritrichomonas foetus causes a venereal disease, trichomoniasis, that usually results in infertility but occasionally causes abortion in the first half of gestation. Placentitis is relatively mild, with hemorrhagic cotyledons and thickened intercotyledonary areas covered with flocculent exudate. The placenta is often retained after abortion. A substantial proportion of cows develop pyometra.

Diagnosis: Bovine fetuses with trichomoniasis have no specific lesions; however, T foetus can occur in abomasal contents, placental fluids, and uterine discharges. Infected cows typically clear the organism within 20 weeks, but bulls, especially those infected after the age of 3 years, can become lifelong carriers.

Treatment and prevention: There is no effective treatment for trichomoniasis in individual cows. Herd control of the disease is based on identification and segregation of pregnant females from at-risk females for ≥ 5 months and on test-and-cull of infected bulls.

Trichomoniasis is prevented via artificial insemination or natural insemination using noninfected bulls. Bulls should be tested when changing ownership, crossing state lines, and 30–60 days before the breeding season each year. Preputial smegma is used to identify the single-celled protozoal parasite.

A killed, whole cell vaccine against T foetus is available for use in cows to help decrease shedding.

The bacterium Trueperella pyogenes causes sporadic abortion in cows at any stage of pregnancy. Rarely, the incidence in a herd can reach epizootic levels (1).

T pyogenes is present in the nasopharynx of many healthy cows and in abscesses. It is not normally present, even as a contaminant, in fetuses or fetal membranes, and isolation is almost always notable.

Diagnosis:T pyogenes gains entry to the bloodstream and causes endometritis and placentitis, which is diffuse and reddish brown to brown in color. The fetus is usually autolyzed and might show fibrinous pericarditis, pleuritis, or peritonitis. Bronchopneumonia might be evident on histological examination of aborted fetuses; however, T pyogenes is best cultured from the placenta or from abomasal contents. Abortion is usually sporadic, and no effective bacterin is available.

Treatment, prevention, and control: There is no specific treatment for T pyogenes–associated abortion. Treatment should be directed toward the primary suppurative infection in the dam, when identified; antimicrobial selection is ideally based on bacterial culture and antimicrobial susceptibility testing (19).

Because T pyogenes is an opportunistic rather than contagious pathogen, prevention focuses on minimizing predisposing conditions, including postpartum uterine disease, retained fetal membranes, dystocia, mastitis, and other sources of tissue infection or bacteremia. Good maternal hygiene and management of chronic suppurative lesions are recommended.

No effective commercial bacterin is currently available for the prevention of T pyogenes–associated abortion. Abortion can also result from hematogenous spread from a remote suppurative focus, not just from primary uterine infection.

The bacterium Ureaplasma diversum is a common inhabitant of the vagina and prepuce of cattle that also causes abortions. Abortions due to U diversum are usually sporadic, but severe outbreaks occasionally occur.

Infection with U diversum can also result in stillbirths and the birth of weak calves. Most fetuses are aborted in the third trimester and are well preserved. The cows are not sick, but retained placentas are common. Placentitis and a necrotic amniotic membrane are common features. The intercotyledonary areas are usually thickened and sometimes contain areas of fibrin deposition and hemorrhage.

There are no gross lesions of U diversum infection in bovine fetuses. Microscopically, there is nonsuppurative placentitis and pneumonia characterized by accumulations of lymphocytes around bronchi and by diffuse alveolitis.

Diagnosis: Diagnosis of U diversum infection is based on isolation of the bacterium from the placenta, fetal lungs, and/or fetal gastric contents (20, 21).

Treatment, prevention, and control: Treatment of U diversum infection is challenging because the organism lacks a cell wall and can persist in the reproductive tract; therefore, beta-lactam antimicrobials are ineffective, and no standardized treatment protocol has been established.

Control of U diversum infection should focus on reproductive hygiene and decreasing venereal or iatrogenic transmission, including appropriate management of bulls, semen, and artificial insemination procedures. Herds with recurrent reproductive disease should be evaluated for concurrent genital tract infections and other predisposing factors.

Because U diversum is a common commensal of the bovine reproductive tract, isolation or PCR assay detection alone does not establish causation and should be interpreted in conjunction with compatible placental and fetal lesions and exclusion of other abortifacient agents.

No effective commercial vaccine against U diversum is currently available.

Akabane virus causes abortion and fetal anomalies.

Occasionally, Salmonella spp cause abortion storms. Affected cows are usually sick, and the fetuses and placentas are autolyzed and emphysematous. Salmonellae can be isolated from the fetus's tissues and gastric contents and from the dam's uterine fluids and feces.

Mycoplasma spp, Histophilus somni, Coxiella burnetii, and a wide variety of other bacteria can also cause sporadic abortions in cattle.

Schmallenberg virus, discovered in Ireland in 2012, has been associated with infertility, abortion, and fetal malformation in several ruminant species (22, 23). Currently, this virus is not known to be present in the US.

• de la Concha-Bermejillo A, Romano J. Pregnancy loss in cattle. Clin Theriogenol. 2021;13(3):167-180.

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