Bacterial Causes of Bovine Infertility and Abortion

CHAPTER 49 Bacterial Causes of Bovine Infertility and Abortion

Bacteria generally are cited as the most common agents of infection causing abortion in cattle. In large retrospective studies, bacterial infections of the fetoplacental unit were identified in 15% to 16.2% of aborted bovines and accounted for 48% to 58% of abortions caused by infectious agents. Abortion in cattle has been associated with more than 25 different species of bacteria, which vary considerably in their pathogenicity for livestock (Table 49-1). It appears that if a bacterium can survive transit in the maternal bloodstream to reach the fetoplacental unit, it has the potential to cause abortion. The fetus may be particularly susceptible to infection by a wide variety of organisms as a result of its immature immune system and suppression of the immune response at the junction of the maternal and fetal placenta.

Table 49-1 Bacterial Agents Associated with Abortion or Stillbirth in Cows*

Agent Frequency (% of total bacteria isolated)
Arcanobacterium pyogenes 29.2
Bacillus spp. 24.8
Listeria 9.4
Escherichia coli 7.6
Leptospira 6.1
Mannheimia hemolytica 2.9
Streptococcus spp. 2.1
Pasteurella multocida 2.0
Salmonella spp. 2.0
Brucella abortus 1.9
Haemophilus somnus 1.6
Staphylococcus spp. 1.6
Campylobacter fetus spp. veneralis 1.5
Campylobacter fetus spp. fetus 1.3
Pseudomonas spp. 1.2

* Bacterial species encountered in 8962 bovine abortions or stillbirths.

Data from Kirkbride CA: Bacterial agents detected in a 10-year study of bovine abortions and stillbirths. J Vet Diagn Invest 1993;5:64.

Diagnostic laboratory data have provided valuable insight into the relative prevalence of bacterial species that contribute to the development of bovine abortion. Unfortunately, similar information is not available for bacterial causes of infertility. Campylobacter fetus spp. veneralis, Leptospira, Mycoplasma, Ureaplasma, Chlamydia, and Haemophilus somnus all have been associated with bovine infertility, but at present the relative prevalence and importance of these agents are unknown.

A number of the bacterial causes of bovine abortion and infertility are potential zoonoses. The agents of these diseases include Leptospira, Brucella, Listeria, Chlamydia, Salmonella, and Campylobacter spp. Care should be taken in handling and transporting the uterine discharge or products of abortion, to minimize or eliminate opportunities for human exposure.


By far the larger portion of this chapter discusses the specific agents recognized as potential causes of bovine abortion. The vast majority of bacterial abortions in cattle (82%), however, are caused by organisms generally considered to be opportunists. These opportunistic organisms fall broadly into two overlapping categories: (1) bacteria that are part of the normal microflora of the mucosal surfaces (Arcanobacterium pyogenes, Pasteurella multocida, Mannheimia hemolytica, Haemophilus somnus, Escherichia coli, Campylobacter spp., Staphylococcus spp. Streptococcus spp.), and (2) common environmental bacteria (Bacillus spp., Pseudomonas sp, E. coli). These ubiquitous bacteria occasionally are able to enter the maternal bloodstream, survive transit to the fetoplacental unit, and cause abortion. Such agents are not considered to be contagious or transmissible causes of abortion.

The significance of isolating one of these agents from an aborted bovine conceptus depends on the incidence of abortion and the clinical signs in the herd. Recovery of any of the aforementioned organisms in isolated abortions generally is of minimal significance from a herd health standpoint. Isolation of one or more species of opportunistic bacteria from fetuses during an outbreak or ongoing abortion problem suggests that (1) access of these ubiquitous organisms to the maternal bloodstream has been enhanced or (2) abortions are a consequence of another disease process.

Although difficult to determine with certainty in retrospect, the occurrence of abortions may be a function of factors that enhance access of ubiquitous bacteria to the maternal bloodstream. Such factors could include subclinical or clinical acidosis (rumenitis), external lesions, or poor feed quality leading to microtrauma in the upper digestive tract. Anecdotal information from diagnostic laboratory submissions would support a link between subclinical or clinical acidosis and bacterial abortion in both dairy and beef cattle.

Pathogens of adult animals, such as Salmonella, Mannheimia hemolytica, H. somnus, and P. multocida, can cause abortion in one of two ways. With the exception of Salmonella, these organisms are ubiquitous members of the normal microflora and can behave as opportunists. They also may cause abortion as a result of disease processes in the adult, in which case abortion is a secondary consequence of the organism’s ability to cause enteric or respiratory disease, with bacteremia leading to fetal infection. Although these agents can be considered contagious pathogens, they typically are not classified as contagious causes of abortion.



Brucellosis once was considered to be the most important reproductive disease of cattle. Today, however, the State-Federal Brucellosis Cooperative Eradication Program, launched in 1934, as well as subsequent programs, has resulted in the elimination of this disease from commercial herds in the Unites States. As of December 2000, no known commercial cattle or bison herds were infected with Brucella in the United States. Currently the only remaining focus of brucellosis in the United States is in the Greater Yellowstone Area, which includes Yellowstone National Park, Grand Teton National Park, the National Elk Refuge, and portions of Idaho, Montana, and Wyoming, where free-ranging bison and elk are infected. These animals pose a disease threat to cattle in surrounding brucellosis-free areas and serve as a potential source for disease reintroduction into domestic cattle and bison herds. Transmission from bison to cattle has been demonstrated when Brucella-infected bison were penned with unvaccinated, seronegative cattle. Documented cases of natural transmission of Brucella from bison or elk to cattle have not been reported, however.

Currently, 46 states, Puerto Rico, and the U.S. Virgin Islands are classified as brucellosis-free, meaning that they have had no infected cattle or domestic bison herds for at least 1 year. Four states—Florida, Missouri, Oklahoma, and Texas–are close to complete eradication of the disease and, with no known infection at this time, are now in the final 1-year countdown phase.

Continued surveillance is necessary to prevent this insidious disease from once again gaining a foothold in U.S. domestic populations. It has been estimated that if brucellosis were allowed to spread, beef and dairy production costs would increase by $80 million within 10 years.

Campylobacter fetus spp. veneralis Infection

Bovine genital campylobacteriosis is a sexually transmitted disease caused by the gram-negative, microaerophilic rod Campylobacter fetus subsp. veneralis. This organism is an obligate parasite of the bovine reproductive tract. Bulls are asymptomatic carriers. The clinical effects of infection are manifested in the cow. Historically, campylobacteriosis has been one of the most important sexually transmitted diseases of cattle. Economic losses are the result of poor conception rates, increased culling due to infertility, decreased average weaning weights, and increased management costs related to prolongation of the calving season.

Agent, Source, and Epidemiology

Campylobacter fetus spp. veneralis is an extracellular, motile, gram-negative, microaerophilic rod. Cattle constitute the primary host and main reservoir for this organism. Reproductive tract infection in cows and young bulls typically is transient. Bulls younger than 3 years of age tend to be resistant to infection and clear the organism within a few weeks. Mature bulls (4 years of age and older) become chronic carriers.

The disease is transmitted by coitus. The transmission rate from infected bulls to susceptible cows may approach 100%. Infected bulls may carry the organism in the preputial cavity indefinitely. Bulls do not become permanent carriers until they are at least 4 years of age, however, and most not until 5 to 6 years of age. The development of epithelial crypts in the penile mucosa with advancing age provides a favorable habitat for the bacteria. Because infection in young bulls is transient, transmission by these animals relies on sexual contact with an infected cow. Bull-to-bull transmission can occur from contaminated semen collection equipment or through mounting activity when bulls are held in common areas.

Cows become infected after natural service by an infected bull or after insemination with contaminated semen. Infection may be spread from cow to cow through the use of poorly sanitized instruments used for reproductive procedures. Infected cows develop immunity and generally clear the organism within 3 to 6 months of infection, and in a majority of cows, Campylobacter will not survive a normal gestation. Some persistently infected cows may harbor the organism for over a year, however, and it has been recovered from cows as long as 196 days beyond the end of pregnancy initiated by infected semen. Failure to eliminate the infection may be due in part to the organism’s ability to undergo substantial antigenic change during the course of natural infection. After clearance of infection, cows are resistant to reinfection for a short period of time.


Diagnosis is based on (1) isolation of the organism, (2) demonstration of the agent in fetal tissues, preputial scrapings, or vaginal mucus with direct fluorescent antibody (FA) tests, or (3) detection of antibodies in vaginal mucus by an enzyme-linked immunosorbent assay (ELISA) or agglutination tests.

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Sep 3, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Bacterial Causes of Bovine Infertility and Abortion

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