Diarrhea, scours or fecal looseness in pigs from birth to market are a common occurrence in hog operations. The causes of the diarrhea are sometimes difficult to pinpoint and, in the following report, we address some reasons why.

Pig’s Gut is a Complex Ecosystem

The intestine of a pig is sterile at birth but will eventually be home to roughly 100 trillion bacteria representing more than 800 different bacterial species. The types of bacteria which ultimately thrive are influenced by dietary nutrient qualities, processes of digestion, the pig’s immune responses and antimicrobial therapies. Pigs benefit from the gut flora/gut bacteria (microbiome) because they help break down portions of the feedstuffs (metabolic benefits), provide vitamins and help to modulate immune functions. This diverse bacterial population is also important in preventing or restricting the growth of harmful, pathogenic infections. A healthy microbiome is important for healthy pigs. Our scientific understanding of how this is achieved has only begun. We mention this here to emphasize that the primary causes of diarrhea are not always infectious.

Diagnosising Diarrhea in Suckling Pigs

Diagnosis of infectious causes of diarrhea is fairly straight-forward if proper samples are submitted to a diagnostic laboratory from acutely affected, non-medicated pigs (Table 1). The diagnostic laboratory performs a variety of tests to confirm a role for infectious agent(s). Most of the infectious agents are opportunists, taking advantage of opportunities that arise due to risk factors. Those factors for suckling piglets include: inadequate colostrum, inadequate milk intake, poor hygiene, cool temperatures/drafts, excess cross-fostering, and porcine reproductive and respiratory syndrome (PRRS) virus. Formalin-fixed samples for histopathology are very important in differentiating common infectious causes of diarrhea.

Diagnosis of suckling pig diarrhea requires multiple 1-in. sections of both small and large intestine in formalin, along with 6-in. segments of ileum, jejunum and colon.

Postweaning and Grow-Finish Diarrhea

The causes of diarrhea in nursery and grow-finish stages are often multifactorial (Figure 1). These may involve noninfectious risk factors (diet, environmental stress, high doses/poor hygiene, compromised vigor from other diseases), as well as infectious insults. Diet and changes in gut physiology after weaning – switching from milk to cereal – also alters the gut flora (microbiome). This activity leads to inflammation and altered gut permeability, which lasts at least a week. The adjustment period allows for pathogenic bacteria to sometimes colonize and cause disease.

The diagnosis of infectious causes of postweaning diarrhea in pigs uses a similar sampling strategy as that used in suckling pigs: multiple 1-in. sections of the small and large intestine in formalin, along with 6-in. segments of ileum, jejunum and colon.

Non-Infectious Diarrhea

Non-specific colitis (dysbacteriosis) is the term used when there is colon dysfunction (diarrhea), but no pathogen is detected. In some cases, the issue is that there is chronic diarrhea and the offending agent is no longer present. In other cases, medication interferes with detection.

There are also noninfectious contributors, such as increased non-starch polysaccharides (NSPs) in the diet, known to cause non-specific diarrhea. This results in elevating total fiber content within the colon and ultimately changing the microbiome. Interestingly, feeding meal diets control non-specific diarrhea better then pelleted feed.

Water quality is thought to contribute to osmotic diarrhea. Total dissolved solids (TDS), including sulfates, are the main areas of interest. Sulfate salts have a laxative effect. There are different maximum recommended levels, depending on the source, for swine. Greater than 3,000 mg/L sulfate can cause transient diarrhea and greater than 7,000 mg/L is not recommended. Higher levels result in diarrhea, mainly in weaned pigs not adapted to poor-quality water. Growth performance is generally not affected by water quality as measured by TDS and sulfates. Higher levels of some minerals and mycotoxins (ochratoxin and vomitoxin or DON) can cause diarrhea.

Ruling out infectious pathogens is usually the first step in investigating causes of diarrhea, along with gathering and recording a complete history, including any changes that may have occurred. Careful interpretation of all available information should occur before assigning a cause. Communication should include everyone involved, including the diagnostician in the laboratory, when trying to diagnose refractory cases of diarrhea in swine herds.