Brucellosis in Cows: Abortion, Testing, and Zoonotic Risk
- See your vet immediately if a pregnant cow aborts, retains the placenta, or several animals have fertility problems. Brucellosis is a reportable disease in the U.S.
- Brucellosis in cattle is usually caused by Brucella abortus. It commonly affects reproduction, especially late-term abortion, weak calves, retained placenta, and reduced conception.
- People can be exposed through aborted fetuses, placentas, uterine fluids, blood, and raw milk. Gloves, eye protection, and careful cleanup matter.
- Diagnosis usually starts with official blood testing through your vet and may be followed by confirmatory testing through state or federal animal health programs.
- There is no routine on-farm curative treatment program for infected cattle in the U.S. Management often centers on testing, isolation, herd control, and culling under regulatory guidance.
What Is Brucellosis in Cows?
Brucellosis is a contagious bacterial disease that mainly affects the reproductive tract of cattle. In cows, the most important species is Brucella abortus. The disease is best known for causing late-term abortion, stillbirth, weak calves, retained placenta, and reduced fertility. Some infected cattle show few outward signs until a pregnancy loss happens.
This condition also matters because it is zoonotic, meaning people can get sick from it. Human exposure can happen during calving, abortion cleanup, necropsy, sample handling, or by consuming raw milk or unpasteurized dairy products from infected animals. Farm workers, veterinarians, slaughterhouse staff, and anyone handling reproductive tissues are at higher risk.
In the United States, bovine brucellosis is tightly regulated through state and federal animal health programs. That means a suspected case is not only a herd health issue. It is also a public health and regulatory issue. If brucellosis is on the list of possibilities, your vet may involve state animal health officials right away.
Symptoms of Brucellosis in Cows
- Late-term abortion, often after the fifth month of pregnancy
- Retained placenta after abortion or calving
- Stillbirth or birth of weak calves
- Infertility, repeat breeding, or lower conception rates in the herd
- Reduced milk production after reproductive loss
- Orchitis, epididymitis, or swollen testicles in bulls
- Occasional joint swelling or hygromas
- No obvious signs until an abortion event occurs
A single abortion does not always mean brucellosis, but any late-term abortion should be taken seriously. See your vet immediately if a cow aborts, if placentas are retained, or if more than one animal has fertility problems. Prompt testing helps protect the rest of the herd and the people working around it.
Use caution around aborted fetuses, placentas, bedding, and uterine discharge. Wear gloves, eye protection, and protective clothing, and keep children, pregnant people, and other animals away from contaminated areas until your vet advises next steps.
What Causes Brucellosis in Cows?
Brucellosis in cattle is most often caused by Brucella abortus, a bacteria that prefers reproductive tissues. Large numbers of organisms can be shed in the placenta, aborted fetus, fetal fluids, vaginal discharge, and milk. That is why calving and abortion events are the highest-risk times for spread.
Cattle usually become infected by licking, sniffing, or ingesting contaminated materials in the environment. Infection can also spread through contact with contaminated equipment, pens, feed areas, or hands and clothing that were exposed to reproductive fluids. Calves may be infected before birth or through nursing.
Herd risk goes up when replacement animals are introduced without adequate testing, when abortion materials are not removed quickly, or when cattle have contact with infected wildlife reservoirs in certain regions. Raw milk use also matters from a human health standpoint, because Brucella can infect people through unpasteurized dairy products.
How Is Brucellosis in Cows Diagnosed?
Diagnosis usually starts with a history and reproductive pattern review. Your vet will ask about recent abortions, retained placentas, weak calves, breeding performance, new herd additions, wildlife exposure, and any people who handled reproductive tissues. Because many diseases can cause abortion in cattle, brucellosis is only one part of the differential list.
Testing often begins with serology, meaning blood tests that look for antibodies to Brucella. In the U.S., official testing and confirmatory testing may be coordinated with state or federal animal health authorities. Positive screening results do not always stand alone, so follow-up testing is often needed before herd-level decisions are made.
If an abortion has occurred, your vet may also recommend submitting the fetus, placenta, and maternal samples for a full abortion workup. This helps rule in or rule out other important causes of pregnancy loss. Because brucellosis is zoonotic and reportable, sample handling should be done with strict biosecurity and according to your vet's instructions.
Treatment Options for Brucellosis in Cows
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Immediate isolation of the aborting cow or suspect animals
- Biosecure cleanup and disposal of placenta, fetus, and contaminated bedding
- Targeted veterinary exam and sample collection
- Focused testing of affected animals first
- Short-term movement restriction while awaiting guidance
- Practical worker protection steps for anyone handling tissues or milk
Recommended Standard Treatment
- Official serologic testing coordinated through your vet and state or federal programs
- Isolation and movement control for suspect or positive cattle
- Whole-herd or risk-based follow-up testing
- Removal of confirmed positive animals from the herd, often by slaughter under regulatory guidance
- Cleaning and disinfection of contaminated areas
- Record review, trace-back, and testing of exposed additions or contacts
Advanced / Critical Care
- Large-scale outbreak investigation and repeated herd surveillance
- Intensive segregation plans for exposed groups
- Expanded abortion diagnostics to rule out coexisting causes of reproductive loss
- Consultation with state veterinarians, APHIS, and herd health specialists
- Enhanced staff PPE protocols and occupational exposure planning
- Facility workflow changes for calving, maternity pens, and carcass or waste handling
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Brucellosis in Cows
Bring these questions to your vet appointment to get the most out of your visit.
- Does this abortion pattern fit brucellosis, or are other causes more likely in my herd?
- Which animals should be tested first, and do we need whole-herd testing now or later?
- What samples should we submit from the cow, fetus, and placenta to get the most useful answers?
- Do we need to report this suspicion to state animal health officials right away?
- How should we isolate affected cows and handle milk, bedding, manure, and aborted tissues safely?
- What personal protective equipment should workers use during calving, abortion cleanup, and sample collection?
- Should we pause animal movement, breeding, or sales until results are back?
- What vaccination, testing, and replacement-animal protocols make sense for this herd going forward?
How to Prevent Brucellosis in Cows
Prevention starts with biosecurity and herd entry control. Work with your vet to review where replacement animals come from, whether testing is needed before purchase or movement, and how new arrivals should be separated before joining the herd. In some risk settings, official calfhood vaccination with RB51 is part of the control strategy under USDA and state guidance.
Abortion management is another major prevention step. Any aborted fetus, placenta, or contaminated bedding should be removed promptly and handled as potentially infectious. Clean and disinfect the area, limit traffic through maternity spaces, and keep dogs, wildlife, and scavengers away from reproductive waste.
Because brucellosis can infect people, prevention also means protecting workers and families. Wear gloves and eye protection when assisting births or handling reproductive tissues, wash thoroughly after contact, and avoid splashes or aerosols. Do not consume raw milk from suspect animals. Pasteurization helps reduce human risk, while raw milk and unpasteurized dairy products can transmit Brucella.
If your farm is in or near an area with wildlife exposure concerns, ask your vet about region-specific risk reduction. A prevention plan that fits your herd, labor setup, and local regulations is usually the most practical long-term approach.