Swine Dysentery in Pigs: Bloody Diarrhea, Causes, and Treatment
- See your vet immediately if your pig has bloody diarrhea, mucus in the stool, weakness, or dehydration.
- Swine dysentery is a contagious large-intestinal disease most often linked to strongly beta-hemolytic Brachyspira species, especially Brachyspira hyodysenteriae.
- It is most common in growing and finishing pigs, but any exposed pig can become ill.
- Early treatment can improve comfort and reduce spread, but your vet usually needs fecal testing, PCR, culture, and herd-level planning.
- Typical US cost range for exam, fecal testing, and initial treatment planning is about $150-$600 for a pet pig case, while herd outbreaks and advanced diagnostics can run $800-$3,500+.
What Is Swine Dysentery in Pigs?
Swine dysentery is a contagious disease of the large intestine that causes mucohemorrhagic diarrhea, meaning stool may contain both mucus and blood. It is classically associated with Brachyspira hyodysenteriae, but other strongly beta-hemolytic Brachyspira species, including B. hampsonii and B. suanatina, can cause a similar syndrome. The disease is most often seen in growing-finishing pigs and can lead to poor weight gain, dehydration, and sometimes death.
In many pigs, the first change is loose stool that quickly becomes more dramatic. Pet parents may notice dark red or tar-like diarrhea, gray mucus, straining, reduced appetite, and a pig that seems dull or tucked up. Because the disease affects the colon, pigs may pass frequent small amounts of stool rather than one large bowel movement.
This is not a condition to monitor at home without veterinary guidance. Bloody diarrhea in pigs has several possible causes, including salmonellosis, proliferative enteropathy, intestinal spirochetosis, and heavy whipworm infection. Your vet can help sort out which problem is most likely and what level of care fits your pig and your household.
Symptoms of Swine Dysentery in Pigs
- Loose stool that progresses to mucus-covered diarrhea
- Bloody diarrhea or dark, tarry stool
- Straining to pass stool
- Reduced appetite or not finishing meals
- Lethargy, weakness, or isolating from other pigs
- Dehydration, sunken eyes, or tacky gums
- Weight loss or poor growth over days to weeks
- Sudden decline in multiple pigs housed together
See your vet immediately if you notice blood in the stool, repeated diarrhea, weakness, or signs of dehydration. Swine dysentery can spread through groups of pigs, and early cases may look mild before worsening quickly. If more than one pig is affected, or if your pig is young, thin, or already ill, the need for prompt veterinary care is even higher.
What Causes Swine Dysentery in Pigs?
Swine dysentery is caused by infection with certain strongly beta-hemolytic Brachyspira bacteria. The best-known cause is Brachyspira hyodysenteriae, but B. hampsonii and B. suanatina are also recognized causes. These bacteria colonize the large intestine and trigger inflammation that leads to mucus, bleeding, and diarrhea.
Pigs usually become infected by swallowing contaminated feces or material from the environment. Shared pens, contaminated boots or tools, transport, and introduction of carrier pigs can all spread infection. Rodents are also important because they can help maintain and move the organism around a property.
Not every exposed pig becomes equally sick. Stress, crowding, mixing pigs from different sources, sanitation problems, and concurrent intestinal disease can make outbreaks worse. Polymicrobial disease is common, so your vet may also consider other infections or parasites that can mimic or worsen dysentery.
How Is Swine Dysentery in Pigs Diagnosed?
Your vet will start with the history, age group affected, housing setup, and the appearance of the stool. Bloody, mucus-rich diarrhea in a growing pig raises concern, but the diagnosis should not be based on stool appearance alone. Several pig diseases can look similar, and treatment choices may change depending on the cause.
Diagnosis often involves fecal PCR, anaerobic culture, and sometimes necropsy or tissue histopathology if a pig has died or must be euthanized. Merck Veterinary Manual notes that confirmation is based on typical large-intestinal lesions together with isolation of strongly beta-hemolytic Brachyspira. PCR is widely used, but culture is still valuable because it helps confirm the hemolytic phenotype and may support antimicrobial decision-making.
Your vet may also recommend testing for other causes of bloody diarrhea, such as Salmonella, Lawsonia intracellularis infection, intestinal spirochetosis, or whipworms. In practical terms, that means the diagnostic plan may range from a focused fecal workup for one pet pig to a broader herd investigation when multiple pigs are affected.
Treatment Options for Swine Dysentery in Pigs
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Prompt exam with your vet
- Isolation from other pigs
- Fecal PCR or targeted stool testing when available
- Oral fluids and electrolyte support if your pig is still drinking
- Early antimicrobial plan chosen by your vet based on likely causes and local resistance patterns
- Basic sanitation review and manure control
Recommended Standard Treatment
- Full veterinary exam and hydration assessment
- Fecal PCR plus culture or additional testing for differentials
- Prescription antimicrobial treatment directed by your vet
- Fluid and electrolyte support, sometimes by injection or short outpatient care
- Pain, fever, and appetite support when appropriate
- Cleaning and disinfection plan, rodent control, and review of pig-to-pig transmission risks
- Recheck testing or follow-up if diarrhea persists
Advanced / Critical Care
- Hospitalization or intensive on-farm veterinary management
- IV or repeated injectable fluid therapy for dehydration or shock
- Expanded diagnostics including culture, susceptibility or MIC-guided planning, CBC/chemistry, and necropsy of affected herd mates when indicated
- Management of severe weakness, anorexia, or multiple-pig outbreaks
- Structured eradication or control program with treatment of carriers, movement control, deep cleaning, and disinfection of vacated areas
- Detailed herd biosecurity review including rodent control and source tracing
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Swine Dysentery in Pigs
Bring these questions to your vet appointment to get the most out of your visit.
- Does my pig's stool pattern fit swine dysentery, or are other causes of bloody diarrhea more likely?
- Which tests do you recommend first: fecal PCR, culture, parasite testing, or bloodwork?
- Does my pig need fluids or hospitalization today, or can care be done safely at home?
- Which antimicrobial options make sense in our area, and do you recommend culture or susceptibility testing?
- How should I isolate my pig and clean the environment to reduce spread?
- Should my other pigs be monitored, tested, or treated based on their exposure?
- What signs mean the plan is not working and my pig needs recheck care right away?
- What is the expected cost range for conservative, standard, and advanced care in this case?
How to Prevent Swine Dysentery in Pigs
Prevention centers on biosecurity, sanitation, and careful pig movement. Avoid introducing pigs from unknown health backgrounds, and quarantine new arrivals before they mix with resident pigs. Clean manure-contaminated areas promptly, keep feed and water sources clean, and reduce crowding when possible. These steps matter because infected pigs and carrier pigs can shed organisms into the environment.
Rodent control is a key part of prevention. Mice and rats can help maintain and spread Brachyspira on a property, so your vet may recommend a structured pest-control plan along with cleaning and disinfection. Boots, tools, trailers, and shared equipment should also be treated as possible sources of spread.
If swine dysentery has already been identified on the property, prevention becomes a herd-management project rather than a one-time cleaning job. Merck Veterinary Manual notes that eradication may be possible without total depopulation, but it requires a persistent plan that can include treatment of carrier pigs, movement control, and thorough cleaning and disinfection of vacated facilities. Your vet can help tailor that plan to one pet pig, a backyard group, or a larger herd.