# Differential Diagnosis of Abortion in Dairy Cattle: Infectious and Non-Infectious Causes ## Key Takeaways - The diagnostic approach to bovine abortion hinges on differentiating sporadic events from abortion storms, with storms (often >10% of the at-risk herd in a defined period) demanding immediate investigation due to potential contagious or zoonotic agents. - Fetal age at loss is a critical discriminator: mid-gestation losses (90-150 days) are characteristic of *Neospora caninum* and BVDV, while late-gestation losses (>180 days) may suggest agents like *Leptospira* spp. or *Listeria monocytogenes*. - Fetal tissues (lung, abomasal contents, liver, placenta) are the highest-yield diagnostic specimens, with PCR and histopathology being key modalities; however, organism detection does not automatically prove causation, and co-infections are common. - Maternal serology is most informative when paired acute and convalescent samples are utilized, demonstrating seroconversion, rather than relying on single high titers, which can be confounded by vaccination or endemic infection. - A negative diagnostic workup is frequent (40-60% of cases), necessitating consideration of non-infectious causes (heat stress, nutrition, genetics) as diagnoses of exclusion after a thorough infectious disease investigation. - Reportable diseases such as *Brucella abortus* require adherence to national surveillance programs and consultation with veterinary authorities, with WOAH standards guiding international reporting obligations. --- Abortion in dairy cattle is a clinical presentation with a wide differential list, and the diagnostic approach differs substantially depending on whether the practitioner faces a single sporadic event or an abortion storm. This article provides a systematic framework for investigating both scenarios in dairy herds, with emphasis on the infectious agents most frequently implicated in mid to late gestation pregnancy loss. The content is written for practicing veterinarians who require a structured diagnostic reasoning process instead of a list of possible causes. The clinical question this reference addresses is direct: when a dairy client reports a cow that has aborted, or several cows that have aborted within a short window, what is the rational sequence of history taking, sample collection, laboratory testing, and interpretation? The answer depends on understanding the epidemiology of each abortifacient, the timing of fetal loss, the value of fetal versus maternal sampling, and the distinction between causation and mere association. A positive PCR result from fetal tissue does not always prove that the detected organizm caused the abortion, and a negative result does not exclude an infectious cause when sampling was delayed or the fetus was autolysed. The economic stakes are considerable. Bovine viral diarrhea virus (BVDV) infection alone produces direct monetary losses that have been quantified across multiple production systems, with average losses per naive dairy cow exceeding those per beef cow in a systematic review of 44 studies covering 15 countries [Richter et al., systematic review of direct monetary losses due to BVDV infection](https://pubmed.ncbi.nlm.nih.gov/28190502/). Neosporosis similarly imposes measurable costs through abortion, premature culling, and reduced milk yield, although the true economic impact has historically been difficult to estimate because vertical transmission inflates seroprevalence figures without a corresponding increase in abortion risk [Trees et al., economic impact of bovine neosporosis](https://pubmed.ncbi.nlm.nih.gov/10576571/). These economic realities justify a disciplined diagnostic workup instead of empirical treatment. ## At a Glance | Parameter | Clinical Decision Point | |---|---| | Abortion definition | Fetal loss between 42 days of gestation and term, varies by reporting jurisdiction | | Sporadic versus storm | Storm generally defined as abortion in more than 10% of the at-risk herd within a defined period, but local definitions vary | | Fetal age estimation | Crown-rump length and fetal hair coat development help narrow the differential list | | Highest priority infectious causes | Neospora caninum, BVDV, Brucella abortus, Leptospira spp., Listeria monocytogenes, Salmonella spp., infectious bovine rhinotracheitis virus | | Maternal serology | Paired acute and convalescent samples are more informative than a single sample | | Fetal sampling | Lung, abomasal contents, liver, and placenta are the highest yield tissues | | Key interpretive trap | Detection of an organizm in fetal tissue does not prove causation, co-infections occur in a measurable proportion of cases | | Reportable diseases | Brucellosis and other agents may be notifiable, consult national veterinary authorities | ## The Diagnostic Logic of Abortion Investigation Abortion investigation differs from most other diagnostic exercises in production medicine because the affected animal is often unavailable for clinical examination. The fetus and placenta are the primary diagnostic specimens, and their condition at the time of collection determines which tests can be performed. Autolysis progresses rapidly after fetal death, and a fetus that has been retained in utero for several days may yield tissue that is unsuitable for histopathology or bacterial culture even when molecular testing remains possible. The first decision point is whether the case is sporadic or epidemic. A single abortion in a herd of several hundred cows is common and often remains undiagnosed despite a thorough workup. An abortion storm, by contrast, demands immediate investigation because the cause may be contagious, zoonotic, or both. The threshold for defining a storm varies by region and by the reporting body, but a practical working definition is abortion in more than 10% of the at-risk pregnant population within a two to four week period. The practitioner should also consider whether the pattern of abortions is clustered in time, by parity, by pen, or by feeding group, because each pattern suggests a different category of cause. ## Gestational Timing and the Differential List Fetal age at the time of loss is one of the most useful pieces of information available to the practitioner. Early embryonic loss, before day 42, is often unrecognized clinically and presents as repeat breeding or extended inter-estrous intervals. Mid gestation losses, between approximately 90 and 150 days, are characteriztic of certain infectious agents. Late gestation losses, after 180 days, raise the possibility of stillbirth instead of true abortion, and the differential list shifts accordingly. Neospora caninum is the most commonly diagnosed infectious cause of bovine abortion in many dairying regions worldwide [Reichel and Ellis, review of Neospora vaccine development and abortion prevention](https://pubmed.ncbi.nlm.nih.gov/19497326/). Infection is transmitted predominantly vertically from dam to calf, and seropositive cows are at substantially higher risk of abortion than seronegative herdmates. In one Australian dairy herd investigation, seropositive cows were 13 times more likely to abort than uninfected cows, and 75% of seropositive animals were related, indicating a high degree of congenital transmission [Hall et al., Neospora abortion diagnosis and transmission in dairy cattle](https://pubmed.ncbi.nlm.nih.gov/15740860/). Neospora-associated abortion typically occurs between 4 and 6 months of gestation, and the fetus is usually autolysed by the time it is expelled. BVDV causes abortion at any stage of gestation, but the pattern depends on whether the dam is acutely infected or persistently infected. Acute infection in a naive dam during the first trimester can lead to embryonic death, while infection between approximately 100 and 150 days may produce fetal malformations, particularly cerebellar hypoplasia and ocular defects. Infection after 180 days often results in seroconversion of the fetus without abortion. The economic impact of BVDV is well documented, and the direct losses per naive dairy cow are measurably higher than those per beef cow, reflecting the greater reproductive and production costs in dairy systems [Richter et al., systematic review of direct monetary losses due to BVDV infection](https://pubmed.ncbi.nlm.nih.gov/28190502/). ## Bacterial Abortifacients and the Role of Co-Infection Bacterial causes of bovine abortion include Brucella abortus, Leptospira interrogans serovars, Listeria monocytogenes, Salmonella enterica, Campylobacter fetus, and Coxiella burnetii. The relative importance of each agent varies geographically, and the practitioner should be guided by regional disease prevalence and by the herd's vaccination history. A survey of mid to late gestation abortions in Tunisian dairy herds detected an infectious agent by PCR in 48.7% of 150 cases, with Brucella spp. the most frequently identified pathogen at 31.3% of cases [Barkallah et al., survey of infectious etiologies of bovine abortion in dairy herds](https://pubmed.ncbi.nlm.nih.gov/24662769/). Notably, 8.7% of cases represented co-infections with two agents, a finding that complicates interpretation of single-agent PCR results. Listeria monocytogenes deserves particular attention in dairy herds because of its association with silage feeding. Poorly fermented or aerobically spoiled silage can support the growth of Listeria, and consumption of contaminated feed can lead to abortion, encephalitis, or septicemia [Queiroz et al., review of foodborne pathogens in silage and mitigation by additives](https://pubmed.ncbi.nlm.nih.gov/29685282/). The diagnosis of Listeria abortion requires culture of the organizm from fetal stomach contents or placenta, and the herd history should include a careful review of feed management, particularly the condition of silage at the feed face and the frequency of aerobic exposure. ## The Distinction Between Association and Causation The central interpretive challenge in abortion diagnosis is distinguishing between an organizm that caused the abortion and an organizm that was present incidentally. This distinction is particularly difficult for Neospora caninum because of its high prevalence in many herds and its efficient vertical transmission. Demonstration of infection in an aborted fetus does not prove that Neospora caused the abortion, and the same caution applies to other agents detected by PCR [Trees et al., economic impact of bovine neosporosis](https://pubmed.ncbi.nlm.nih.gov/10576571/). The practitioner should therefore interpret laboratory results in the context of the herd's seroprevalence, the gestational timing of the abortion, the fetal lesion pattern, and the presence or absence of other potential causes. A diagnosis of infectious abortion is most secure when the agent is detected in fetal tissue in the presence of compatible lesions, or when maternal seroconversion is demonstrated with paired samples. A single high maternal titer is suggestive but not diagnostic, particularly in herds where vaccination is practiced. The practitioner should also be aware that some agents, such as Brucella abortus, are reportable in many jurisdictions, and the diagnostic workup may be governed by national surveillance programs instead of by clinical judgment alone. The World Organization for Animal Health publishes terrestrial animal health standards that define the reporting obligations for listed diseases, and the practitioner should consult these standards and the relevant national veterinary authority when a reportable disease is suspected [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). ## The Abortion Workup: From Herd Visit to Laboratory The investigation begins with a herd visit, not a laboratory submission. A complete reproductive history, including the number of at-risk pregnant cows, the gestational ages of aborted fetuses, and the temporal pattern of abortions, determines which samples matter and which tests will be informative. A single abortion in a 500-cow herd warrants a different intensity of investigation than three abortions in a week. The first decision point is whether the herd is experiencing an abortion storm or sporadic losses. Sporadic abortion, defined as fewer than 2% of pregnancies lost over a 30 day period, usually reflects individual cow factors such as twinning, placental insufficiency, or endemic infection. An abortion storm, typically 5% or more of the at-risk population aborting within a defined period, shifts the differential toward contagious agents including bovine viral diarrhea virus (BVDV), infectious bovine rhinotracheitis virus, leptospirosis, and neosporosis. The economic weight of these losses is substantial. A systematic review of BVDV direct monetary losses across 44 studies in 15 countries found average direct losses per naive dairy cow were USD 24.85 higher than per beef cow, with abortion among the significant drivers of that cost. ### The Herd-Level Assessment Sequence Work through the following sequence in order, because each step modifies the interpretation of the next. 1. **Establish the abortion rate.** Count confirmed abortions, also observed abortions. Many early fetal losses are resorbed or passed unnoticed. Use palpation or ultrasound pregnancy checks to identify cows that were pregnant and are no longer. Compare the current 30 day abortion rate to the herd baseline. 2. **Plot the epidemic curve.** Abortions clustered in a 2 to 4 week window suggest an infectious point source or a common exposure such as contaminated feed. A smouldering pattern over months points to endemic infection, often Neospora caninum or BVDV. In one Australian dairy herd investigation, seropositive cows were 13 times more likely to abort than uninfected herdmates, and 75% of seropositive animals were related, indicating predominantly vertical transmission. 3. **Stage the abortions.** Fetal age at abortion narrows the differential. Mid gestation losses (4 to 7 months) are typical of Neospora, BVDV, and fungal placentitis. Late losses (7 to 9 months) are more consistent with leptospirosis, listeriosis, and Salmonella. The gestational timing section in part 1 of this article provides the full staging framework. 4. **Inspect the fetus and placenta.** Submit the fetus and placenta for necropsy whenever feasible. Fetal autolysis does not preclude diagnosis. The placenta is often more diagnostically valuable than the fetus itself, particularly for fungal and Neospora infections. Examine the cotyledons for necrosis, exudate, or thickening, and note the fetal lesions including subcutaneous edema, hepatomegaly, and serosanguinous effusions. 5. **Review the feed and environment.** Poorly fermented silage is a recognized source of Listeria monocytogenes, which can cause abortion in dairy cows. Ask about silage quality, feed-out practices, access to standing water, wildlife ingress, and recent introductions of replacement stock. ### Sample Collection and Submission The quality of the laboratory diagnosis depends on the completeness of the submission. Collect the following from each abortion case: | Sample | Container | Target Pathogens | Notes | |---|---|---|---| | Fetal abomasal contents | Sterile plain tube | Leptospira, Salmonella, Listeria, Brucella | Collect before fetal manipulation | | Fetal lung | Sterile plain tube and formalin | BVDV, bacterial pathogens | Frozen tissue for PCR, formalin for histology | | Fetal liver | Sterile plain tube and formalin | BVDV, Leptospira, Neospora | PCR panel | | Fetal kidney | Sterile plain tube | Leptospira | | | Placenta (cotyledon and intercotyledonary tissue) | Sterile plain tube and formalin | Neospora, fungi, Brucella | Include both affected and unaffected areas | | Maternal serum | Clot tube | BVDV, Neospora, Leptospira, IBR | Acute sample within 48 hours of abortion | | Maternal paired serum | Clot tube | Leptospira, IBR | Convalescent sample 2 to 4 weeks later | A pan-Chlamydiales PCR approach has demonstrated the value of broad molecular screening. In a survey of 150 mid to late gestation abortion cases from 20 dairy herds, infectious agents were detected in 48.66% of cases, with 8.66% representing co-infections. Brucella spp. was the most common at 31.3%, followed by Waddlia chondrophila at 8% and Parachlamydia acanthamoebae at 5.33%. This finding underscores two practical points. First, a single pathogen PCR panel will miss a meaningful proportion of diagnoses. Second, co-infections are common enough that a positive result for one agent should not terminate the diagnostic workup. ### Interpretation of Laboratory Results Interpretation depends on the test modality and the population context. Serology on a single aborted cow is rarely diagnostic. A positive Neospora titre in an aborted cow confirms exposure, not causation, because vertical transmission is so efficient that many infected cows never abort. The diagnosis of Neospora abortion requires either fetal histopathology showing non-suppurative encephalitis and myositis, or PCR detection of the organizm in fetal brain tissue. Serology is more useful at the herd level, where the prevalence of seropositive cows can be compared against the abortion rate. For BVDV, detection of viral RNA or antigen in fetal tissue is diagnostic of transplacental infection. Maternal serology is complicated by vaccination and by the fact that persistently infected animals may be seronegative. The economic case for identifying BVDV as the cause of abortion is strong, given the documented direct monetary losses associated with the infection. Leptospirosis requires paired serology for a definitive diagnosis. A single high titre in an aborted cow is suggestive but not confirmatory, particularly in vaccinated herds. A fourfold rise in titre between acute and convalescent samples, or detection of leptospires in fetal tissues by PCR or silver staining, confirms the diagnosis. ### When the Workup Is Negative A negative diagnostic workup is the rule instead of the exception. Most surveys of bovine abortion fail to identify a cause in 40% to 60% of cases, even with comprehensive testing. The causes of this diagnostic gap include autolysis of submitted fetuses, sampling error, pathogens not covered by the testing panel, and non-infectious causes that leave no fetal lesion. Non-infectious causes including heat stress, nutritional deficiencies, and genetic abnormalities are diagnoses of exclusion that require a complete infectious workup before they can be invoked. The distinction between association and causation, discussed in part 1, is central here. Detection of an organizm in fetal tissue does not prove it caused the abortion. The organizm must be present in a lesion consistent with its known pathogenicity, or the epidemiological pattern must support a causal role. This standard is particularly important for organizms such as Waddlia chondrophila and Parachlamydia acanthamoebae, whose role in bovine abortion is still being defined. ### Documentation and Reporting Record every step of the investigation in the herd health record. Include the abortion rate calculation, the epidemic curve, the gestational ages of affected fetuses, the samples submitted, the laboratory results, and the interpretation. This documentation serves three purposes. It provides the baseline for monitoring the effectiveness of any interventions. It supports the herd-level diagnosis when the pattern of losses is more informative than any single case. It also creates the record needed for regulatory reporting where abortion is a notifiable disease. The World Organization for Animal Health maintains international standards for surveillance and reporting of transboundary diseases, and national veterinary authorities define which abortifacients are reportable in their jurisdiction. The USDA Animal and Plant Health Inspection Service provides the corresponding national program information for the United States. The workup is complete when the herd-level pattern, the fetal and placental findings, and the laboratory results converge on a coherent diagnosis, or when the infectious differential has been reasonably excluded and management factors become the focus. ## Recognized Complications and Failure Modes Abortion investigations fail most often at the interface between herd-level data and laboratory interpretation. The first recognized failure mode is confirmation bias, where a positive PCR result for a known abortifacient ends the investigation despite epidemiological evidence that the detected agent does not explain the outbreak pattern. A positive result for *Neospora caninum* in a herd with an abortion storm, for example, requires scrutiny. Neospora typically causes sporadic abortion and endemic infection, and the association between seropositivity and abortion risk is well established, but a clustered storm pattern should prompt a search for a second agent. The discriminating check is gestational timing and spatial clustering. Neospora abortions cluster in time but not by pen or feed group, whereas nutritional or toxic causes cluster by management group. The second failure mode is over-reliance on maternal serology. A single maternal titre confirms exposure, not causation. Paired acute and convalescent samples, or demonstration of a rising titre in a cow that aborts, carry more weight. For *Brucella abortus*, serology is the primary diagnostic tool, but for most other agents the fetus and placenta are the diagnostic specimens of choice. Submission of only maternal blood is the most common sample error and the most preventable. The third failure mode is misinterpretation of co-infections. In one survey of mid to late gestation abortions, co-infection with two agents was detected in 8.66% of cases. Detection of two organizms does not establish that either caused the abortion. The clinician must rank organizms by pathogenicity, fetal lesion association, and gestational timing. A non-pathogenic commensal detected alongside *Listeria monocytogenes* should not dilute the diagnosis. The fourth failure mode is failure to recognize the herd-level pattern. A single abortion may be investigated as an isolated event, but the threshold for herd investigation should be low. Two or more abortions within a defined period, typically two to four weeks, or an abortion rate exceeding 5% in a calving season, warrants a structured herd investigation. Waiting for a third or fourth abortion before acting loses diagnostic opportunity because fetal autolysis progresses rapidly. ## Common Errors and Corrective Actions Less experienced clinicians commonly submit only the fetus without placenta or maternal blood. The placenta is frequently the highest-yield specimen for bacterial culture, particularly for *Brucella*, *Listeria*, and *Campylobacter*. Submission of the entire fetus chilled, not frozen, with placenta and paired maternal serum, maximizes diagnostic yield. A second common error is freezing the fetus before laboratory submission. Freezing destroys histologic architecture and renders immunohistochemistry and fluorescence techniques unreliable. Chilled transport within 24 to 48 hours is preferred. If delivery is delayed, formalin-fixed tissues for histology should be collected at the farm and chilled tissues sent separately. A third error is interpreting a negative laboratory result as proof of non-infectious cause. Diagnostic sensitivity for bovine abortion is imperfect, and a negative workup does not exclude infectious aetiology. The proportion of abortions with no definitive diagnosis in published surveys remains substantial, and this should be communicated to the producer as a limitation, not a conclusion. A fourth error is neglecting feed-related causes. Poorly fermented silage or silage with aerobic spoilage can harbour *Listeria monocytogenes*, which causes abortion and encephalitis. Feed history, silage quality assessment, and culture of feed samples should be part of the workup when bacterial abortion is suspected and no fetal pathogen is identified. ## Limitations of the Evidence and Areas of Expert Disagreement The evidence base for bovine abortion diagnosis is constrained by several factors. Most published surveys are regional and may not reflect pathogen prevalence in other production systems. The Tunisian survey that identified *Waddlia chondrophila* and *Parachlamydia acanthamoebae* in aborted fetuses illustrates both the value of broad molecular screening and the difficulty of assigning causation to emerging organizms. Detection of DNA does not prove pathogenicity, and expert opinion differs on whether these organizms are primary abortifacients or opportunists. Economic assessments of abortion losses vary widely. Direct monetary losses from BVDV infection ranged from 0.50 to 687.80 USD per animal across 44 studies, a heterogeneity that reflects differences in production systems, study design, and calculation methods. Clinicians should be cautious when citing economic impact figures to producers, as local conditions may differ substantially from published estimates. Expert opinion also differs on the value of vaccination for *Neospora caninum*. Despite decades of research, an efficacious vaccine that reliably prevents abortion has not been developed, and available vaccines are not universally licensed. Control therefore rests on identifying and culling seropositive animals, avoiding breeding from infected dams, and reducing postnatal exposure. Some practitioners advocate blanket serologic testing and culling, while others prefer targeted testing of aborting cows only. Both approaches have merit depending on herd prevalence and replacement costs. ## Escalation, Referral, and Regulatory Reporting Referral to a veterinary diagnostic laboratory should occur early, not after a failed farm-level workup. Most diagnostic laboratories offer abortion panels that include bacterial culture, PCR for common abortifacients, histology, and serology. Consultation with a veterinary microbiologist or pathologist before sample submission can improve specimen selection and test ordering. Specialist consultation is warranted when the abortion pattern suggests a notifiable disease, when human health is at risk, or when the herd has failed to respond to standard diagnostic and control measures. Zoonotic agents, including *Brucella*, *Coxiella burnetii*, and *Listeria monocytogenes*, require coordination with public health authorities and clear communication with farm workers about personal protective measures. Regulatory reporting obligations vary by jurisdiction. In the United States, state animal health officials and the USDA APHIS should be contacted when a notifiable disease is suspected. International standards for reporting and trade-related disease control are set by the World Organization for Animal Health, and veterinarians working in export-oriented herds should be familiar with these requirements. The FAO provides additional technical guidance on livestock disease surveillance and animal health services in different production systems. When in doubt about reporting obligations, contact the relevant authority before the investigation proceeds further. | Observation | Likely Cause | Discriminating Check | | --- | --- | --- | | Abortion storm, all feed groups affected | Infectious agent with airborne or vector spread | Compare attack rate by pen and feed group | | Abortions cluster in one pen or feed group | Nutritional, toxic, or silage-related cause | Feed analysis, silage culture, water testing | | Positive PCR for *Neospora* but storm pattern | Co-infection or misattribution | Histology of fetal brain, paired serology, check for second agent | | Negative fetal workup | Autolysis, sampling error, or undetected agent | Review sample handling, submit placenta and paired serum | | Rising maternal titres but no fetal lesion | Exposure without causation | Fetal histology, culture, and PCR for the suspect agent | | Recurrent abortions in same cow | Non-infectious cause, e.g. chromosomal or metabolic | Review individual cow history, uterine examination, metabolic profile | ## Frequently Asked Questions ### How Should I Prioritize Testing When the Herd Has a Limited Diagnostic Budget? Begin with the fetus and placenta, as these provide the highest diagnostic yield. If only maternal samples are possible, collect paired sera for BVDV and Neospora caninum serology, plus a whole blood sample for PCR. When funds are constrained, test the fetus first for BVDV, Neospora, and Brucella abortus, as these are the most common identifiable causes in many regions. A pooled approach, testing several fetuses together for the same agents, can reduce costs while retaining sensitivity for herd-level diagnosis. Discuss cost thresholds with your diagnostic laboratory before submission. The economic impact of BVDV infection, including abortion losses, has been quantified in systematic reviews and can justify a more complete workup when the herd has recurrent losses ([systematic review of direct monetary losses due to BVDV](https://pubmed.ncbi.nlm.nih.gov/28190502/)). ### What Can I Do When the Fetus Is Not Submitted or Is Too Autolysed for Testing? Autolysed fetal tissue still has diagnostic value. PCR-based assays for BVDV, Neospora caninum, and Leptospira spp. are often more tolerant of tissue degradation than virus isolation or histopathology. Collect ear notch, spleen, kidney, and brain even when the fetus is macerated. Maternal serology becomes the primary tool in this situation. Paired samples taken three weeks apart can detect seroconversion to BVDV, Leptospira, and Neospora. A single high titre to Neospora in a cow that has aborted is suggestive but not confirmatory, because vertical transmission produces persistently seropositive animals that may abort for other reasons ([Neospora abortion diagnosis and transmission](https://pubmed.ncbi.nlm.nih.gov/15740860/)). Placenta, if available, should be examined grossly and submitted for histology and PCR, as it often retains diagnostic material longer than the fetus. ### How Do I Distinguish a True Abortion Storm From a Cluster of Sporadic Abortions? A true abortion storm is defined by a sharp increase in abortions above the herd baseline within a short period, typically two to four weeks. Investigate immediately when the monthly abortion rate exceeds 5 percent of the pregnant herd or when multiple abortions occur within a single week. Sporadic clusters often reflect endemic Neospora infection, where seropositive cows abort at higher rates than seronegative herdmates. In one herd investigation, seropositive cows were 13 times more likely to abort than uninfected cows, with most infections vertically transmitted ([Neospora abortion risk in dairy cattle](https://pubmed.ncbi.nlm.nih.gov/15740860/)). A true storm more often implicates an infectious agent with a common source, such as BVDV, leptospirosis, or a feedborne pathogen like Listeria monocytogenes. The distinction matters because it changes the urgency of biosecurity measures and the focus of the laboratory investigation. ### What Is the Most Practical Way to Investigate Abortions When the Herd Is Not Enrolled in a Health Program? Start with a structured herd visit even without an existing program. Review abortion records, calving dates, and breeding records to establish the gestational timing and pattern of losses. Examine the current diet, with particular attention to silage quality, as poorly fermented silage can harbour Listeria and other abortifacient pathogens ([foodborne pathogens in silage](https://pubmed.ncbi.nlm.nih.gov/29685282/)). Collect blood from aborting cows and a sample of unaffected pregnant herdmates for comparison. Submit the fetus and placenta if available. Many diagnostic laboratories offer abortion investigation panels that bundle testing for the most common agents at a reduced price. National and international animal health agencies publish guidance on surveillance and diagnostic approaches that can be adapted to herds without formal health programs ([WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/)). ### How Should I Document Abortion Cases to Support Future Herd-Level Analysis? Record each abortion with the cow identification, abortion date, gestational age, dam parity, and any observed clinical signs. Note whether the fetus and placenta were examined and what samples were collected. Maintain a spreadsheet or herd management software entry that allows you to calculate monthly abortion rates and identify temporal or spatial clustering. Photograph gross lesions and laboratory submissions. Record all laboratory results, including negative findings, as these are essential for interpreting future cases. Documentation also supports regulatory reporting where required. The MSD Veterinary Manual provides guidance on record keeping and diagnostic interpretation that can be applied to abortion investigations ([MSD Veterinary Manual professional edition](https://www.msdvetmanual.com/)). ### How Do I Explain a Negative Diagnostic Workup to the Herd Owner Without Undermining Confidence? Frame the negative result as useful information, not failure. Explain that a complete workup identifies a cause in roughly half of cases, and that negative results rule out the most common infectious agents. Emphasize that some causes, particularly early embryonic loss and toxic insults, are difficult to confirm after the event. Discuss the possibility of endemic Neospora infection, where seroprevalence in the herd may be high but only a fraction of infected cows abort in any given pregnancy ([economic impact of bovine neosporosis](https://pubmed.ncbi.nlm.nih.gov/10576571/)). Recommend monitoring the next 30 to 60 days of pregnancies and repeating the workup if the abortion rate does not return to baseline. Offer practical next steps, such as reviewing biosecurity, vaccination status, and feed quality, while acknowledging that some abortion problems resolve without a definitive diagnosis. ## Related Clinical & Scientific Guides * [Rumen Health Assessment in Dairy Cows: Clinical and Subclinical Indicators](/knowledge/veterinary-medicine/food-animal-medicine/rumen-health-assessment-dairy-cows-clinical-subclinical-indicators) * [Mastitis Control Programs in Dairy Herds: Monitoring and Prevention](/knowledge/veterinary-medicine/food-animal-medicine/mastitis-control-programs-dairy-herds-monitoring-prevention) * [Swine Nutrition and Health: Feed-Related Disease Diagnosis](/knowledge/veterinary-medicine/food-animal-medicine/swine-nutrition-health-feed-related-disease-diagnosis) ## References and Further Reading - [A systematic worldwide review of the direct monetary losses in cattle due to bovine viral diarrhea virus infection.](https://pubmed.ncbi.nlm.nih.gov/28190502/). 2017. - [Survey of infectious etiologies of bovine abortion during mid- to late gestation in dairy herds.](https://pubmed.ncbi.nlm.nih.gov/24662769/). 2014. - [Neospora caninum--how close are we to development of an efficacious vaccine that prevents abortion in cattle?](https://pubmed.ncbi.nlm.nih.gov/19497326/). 2009. - [Silage review: Foodborne pathogens in silage and their mitigation by silage additives.](https://pubmed.ncbi.nlm.nih.gov/29685282/). 2018. - [Towards evaluating the economic impact of bovine neosporosis.](https://pubmed.ncbi.nlm.nih.gov/10576571/). 1999. - [Neospora abortions in dairy cattle: diagnosis, mode of transmission and control.](https://pubmed.ncbi.nlm.nih.gov/15740860/). 2005. - [USDA APHIS Animal Health Information](https://www.aphis.usda.gov/livestock-poultry-disease). USDA APHIS. - [FAO Animal Production and Health](https://www.fao.org/animal-production/en/). FAO. - [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual. ## Related Articles - [Differential Diagnosis of Sudden Death in Dairy Cattle: Metabolic, Toxic, and Infectious Causes](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-sudden-death-dairy-cattle) - [Differential Diagnosis of Nervous Signs in Cattle: From Metabolic to Infectious](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-nervous-signs-cattle-metabolic-infectious) - [Differential Diagnosis of Egg Drop in Laying Hens: Infectious and Management Causes](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-egg-drop-laying-hens-infectious-management) - [Differential Diagnosis of Ocular Lesions in Cattle: Infectious, Traumatic, and Neoplastic](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-ocular-lesions-cattle-infectious-traumatic-neoplastic) - [Differential Diagnosis of Skin Lesions in Poultry: Infectious and Management Causes](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-skin-lesions-poultry-infectious-management) > This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.