Colitis in Pigs: Causes of Large Bowel Inflammation and Mucus in Stool

Colitis is inflammation of the large intestine. In pigs, that usually means the cecum, colon, or rectum are irritated and inflamed. When the large bowel is affected, stool often becomes more frequent, smaller in volume, and coated with mucus. Some pigs also strain to pass stool or pass fresh red blood.

This is a symptom pattern, not one single disease. In pet pigs and small backyard groups, colitis can happen because of infection, parasites, sudden feed changes, stress, or unsanitary housing. In production-age pigs, one of the best-known large-bowel diseases is swine dysentery, a mucohemorrhagic diarrhea syndrome linked to Brachyspira bacteria that primarily affects the large intestine.

Large-bowel inflammation matters because pigs can dehydrate faster than many pet parents expect. Ongoing diarrhea also affects appetite, weight gain, comfort, and in contagious cases, other pigs in the household or group. That is why early veterinary evaluation is important, especially when mucus, blood, or multiple sick pigs are involved.

In pigs, colitis is often caused by infectious disease. A major cause of large-bowel inflammation is swine dysentery, which is classically associated with Brachyspira hyodysenteriae and can also involve B. hampsonii or B. suanatina. These bacteria spread by the fecal-oral route and damage the large intestine, leading to excess mucus, bleeding, and diarrhea. Salmonella can also inflame the lower intestine, cecum, and spiral colon, and stool may contain mucus, fibrin, or blood.

Parasites are another possibility. Trichuris suis whipworms live in the cecum and large intestine, and heavy infections can cause inflammatory lesions, diarrhea, and poor growth. In younger piglets, coccidial infections are more often a small-intestinal problem, but some coccidia can extend into the cecum and colon and contribute to diarrhea and poor thrift.

Not every case is infectious. Sudden feed changes, spoiled feed, overcrowding, transport stress, poor hygiene, and contaminated water can upset the intestinal environment and make colitis more likely. In real-world cases, there may be more than one factor at once. A pig under stress with a diet change and parasite burden may develop worse signs than a pig with only one issue.

Because several causes can look similar from the outside, it is safest not to assume mucus in stool is a minor problem. Your vet may need to sort out whether this is a self-limited irritation, a parasite issue, or a contagious disease that needs faster action.

Your vet will start with history and exam findings. Helpful details include your pig's age, whether the problem started after a feed change, whether there is blood or mucus, whether other pigs are affected, and whether there have been recent additions, travel, or exposure to shared equipment. On exam, your vet will assess hydration, body condition, temperature, abdominal comfort, and the character of the stool.

Fecal testing is often the next step. Depending on the case, your vet may recommend fecal flotation for parasites, direct fecal evaluation, or laboratory PCR testing and culture for infectious causes. For suspected swine dysentery, diagnostic labs commonly use PCR on feces or fecal swabs to detect Brachyspira organisms. In some cases, necropsy and histopathology are needed to confirm the exact cause, especially during herd outbreaks or when pigs die suddenly.

Diagnosis is also about ruling out look-alike problems. Small-intestinal diarrhea, coccidiosis in piglets, salmonellosis, dietary upset, and other enteric infections can overlap. That is why treatment should be based on your vet's exam and testing plan rather than stool appearance alone.

Prevention starts with clean housing, clean water, and steady routines. Remove manure regularly, keep feeders and waterers clean, and avoid sudden feed changes when possible. Good sanitation lowers exposure to fecal pathogens, and consistent nutrition helps support a healthier gut environment.

Quarantine new pigs before introducing them to resident pigs, and avoid sharing equipment, boots, or transport surfaces without cleaning and disinfection. This matters because important causes of colitis, including swine dysentery, spread through fecal contamination and contaminated environments. If one pig develops diarrhea, separate it promptly and talk with your vet about biosecurity.

Parasite control also matters. Your vet can help you build a deworming and fecal monitoring plan based on your pig's age, environment, and exposure risk. Routine observation is part of prevention too. Catching soft stool, mucus, reduced appetite, or slower growth early gives you more treatment options and may prevent a larger outbreak.