# Differential Diagnosis of Diarrhea in Growing Pigs: Nutritional vs. Infectious Etiologies ## Key Takeaways - Differentiating nutritional diarrhea from infectious etiologies in growing pigs hinges on distinct clinical patterns: nutritional diarrhea often presents with abrupt onset post-feed change, high morbidity, low mortality, absence of fever, and rapid improvement with feed withdrawal. Infectious diarrhea may exhibit more gradual or explosive spread, variable morbidity, potentially high mortality, presence of fever, and less response to feed withdrawal. - Key diagnostic steps involve a systematic approach starting with herd-level epidemiology, including temporal patterns relative to feed delivery and pig movement, followed by physical examination for fever and depression. Feed analysis for protein, calcium, and salt levels, along with feeder function and water intake assessment, are critical for nutritional differentials. - Infectious diarrhea is strongly suggested by the presence of fever (>40.0°C), depression, reduced feed intake, and fecal characteristics such as mucus, blood, or necrotic debris, necessitating fresh fecal sampling for bacterial culture (e.g., *Salmonella*, *Brachyspira*) and PCR for viral agents. - Feed withdrawal for 24-48 hours serves as a valuable low-cost diagnostic test; rapid improvement indicates a nutritional or management cause, while minimal improvement suggests an underlying inflammatory or secretory infectious process. - Laboratory diagnostics should be targeted based on clinical suspicion: feed analysis for nutritional causes, bacterial culture and PCR for infectious agents, and histopathology from necropsy of acutely affected, untreated pigs for definitive diagnosis of mucosal damage. - Common diagnostic errors include misclassifying infectious outbreaks as nutritional problems due to partial response to feed correction, overinterpreting single diagnostic tests without clinical correlation, and neglecting water delivery systems as potential vectors for disease transmission. --- Diarrhea in grow-finish pigs presents a diagnostic challenge distinct from neonatal or nursery scours. The differential list is broad, the economic impact of misdiagnosis is substantial, and the distinction between nutritional, infectious, and management-related causes often determines whether intervention targets feed formulation, housing, or pathogen control. This article provides a structured diagnostic framework for the practicing veterinarian evaluating diarrhea in pigs from approximately 10 weeks of age through market weight. The clinical question is rarely whether diarrhea exists, but rather why it exists in this group, at this stage, and with this pattern of morbidity and mortality. Grower pigs face simultaneous transitions in diet composition, gut microbiota maturation, pen social structure, and environmental pathogen pressure. Each of these variables can produce clinically indistinguishable fecal changes. The diagnostic approach therefore depends on systematic data collection, careful epidemiologic pattern recognition, and targeted laboratory confirmation instead of reflexive antimicrobial therapy. This reference covers the physiologic basis of diarrhea in growing pigs, the specific nutritional and management triggers, the major infectious differentials, and a practical diagnostic workup algorithm. Treatment and control strategies are addressed elsewhere. The focus here is diagnostic reasoning: how to separate causes that require feed changes from those that require biosecurity interventions, vaccination, or antimicrobial stewardship decisions. ## At a Glance | Parameter | Nutritional/Management | Infectious | |---|---|---| | Onset pattern | Often abrupt after feed change or intake error | May be gradual or explosive, often spreads pen to pen | | Morbidity | High, often 30% to 80% of group | Variable, 10% to 50% typical | | Mortality | Low unless severe acidosis or dehydration | Can be high with swine dysentery or salmonellosis | | Fever | Absent | Common with systemic infections | | Fecal character | Watery, undigested feed particles, normal color | Mucus, blood, fibrin casts suggest infectious colitis | | Response to feed withdrawal | Rapid improvement within 24 to 48 hours | Partial or no improvement | | Laboratory findings | No significant pathogen on culture or PCR | Pathogen identified, often with consistent histopathology | | Key diagnostic step | Feed analysis, intake records, feeder function check | Fresh fecal sampling, necropsy with intestinal histopathology | ## Physiology of Diarrhea in the Growing Pig Diarrhea represents a failure of intestinal fluid and electrolyte homeostasis. In growing pigs, the dominant mechanisms are osmotic diarrhea, secretory diarrhea, and inflammatory or exudative diarrhea. These mechanisms are not mutually exclusive, and many clinical cases involve more than one. Osmotic diarrhea occurs when undigested or unabsorbed solutes remain in the intestinal lumen, drawing water into the gut by osmotic force. In growing pigs, the most common triggers are dietary: excess protein, sudden increases in feed intake, inadequate fiber adaptation, or ingredients with poor digestibility. The small intestine has substantial reserve capacity for absorption, but when luminal solute load exceeds that capacity, fluid spills into the large intestine. The large intestine can absorb some of this fluid, but when the volume or osmotic load overwhelms colonic capacity, diarrhea results. Secretory diarrhea results from active ion secretion, typically chloride, into the intestinal lumen. This mechanism is classically associated with enterotoxigenic *Escherichia coli* (ETEC), which produces heat-labile and heat-stable enterotoxins that activate cyclic nucleotide pathways in enterocytes. The pathogenic schemes of diarrheagenic *E. coli* are well characterized and underlie distinct clinical syndromes, as described in the review of diarrheagenic *E. coli* by Nataro and Kaper. While ETEC is most commonly associated with neonatal and post-weaning diarrhea, enterotoxigenic strains can contribute to diarrhea in older pigs under conditions of stress or concurrent disease. Inflammatory diarrhea results from mucosal damage, often with necrosis, ulceration, and protein loss. This mechanism characterizes the invasive bacterial enteritides such as *Salmonella* and *Brachyspira hyodysenteriae*, as well as porcine proliferative enteropathy caused by *Lawsonia intracellularis*. Inflammatory diarrhea is frequently accompanied by systemic signs including fever, lethargy, and reduced feed intake. ## Nutritional Causes of Diarrhea ### Feed Formulation Errors The most common nutritional cause of diarrhea in grower pigs is an abrupt change in diet composition. Grower diets typically contain higher protein and energy density than nursery diets, and the transition requires a period of enzymatic and microbial adaptation. When the transition is compressed or skipped, undigested protein reaches the large intestine, where microbial fermentation produces osmotically active metabolites and irritant compounds. Protein source matters as well. Soybean meal is highly digestible but contains oligosaccharides such as raffinose and stachyose that are not digested by porcine enzymes. These carbohydrates are fermented in the large intestine, producing gas and osmotic load. Diets with excessive soybean meal inclusion, particularly in the first grower phase, can cause transient diarrhea that resolves as the microbiota adapts. ### Feed Intake and Feeding System Failures Feed intake patterns influence diarrhea risk independently of diet composition. Pigs that are feed-restricted and then given ad libitum access, or pigs that experience feeder malfunction with intermittent starvation and gorging, develop diarrhea from sudden luminal solute load. This pattern is common after feeder adjustment errors, feed delivery interruptions, or mixing of pigs from different feeding regimens. Water intake interacts with feed intake in ways that affect fecal consistency. Pigs that consume excessive water, often due to nipple drinker malfunction or high environmental temperature, produce dilute feces that may be mistaken for diarrhea. Conversely, inadequate water intake can concentrate feed in the stomach and small intestine, leading to impaction and subsequent osmotic diarrhea when water becomes available. ### Mycotoxins and Feed Contaminants Mycotoxin contamination of feed ingredients can cause diarrhea in growing pigs, though the clinical presentation varies by toxin. Deoxynivalenol (vomitoxin) causes feed refusal and reduced intake at low concentrations, but at higher concentrations it induces vomiting and diarrhea through direct irritation of the gastrointestinal mucosa. Fumonisins and aflatoxins produce more systemic effects, with diarrhea as a secondary finding. Feed contamination with non-mycotoxin agents, including excessive mineral salts, rancid fats, or improperly processed ingredients, can also produce diarrhea. The diagnostic approach to suspected feed-related diarrhea includes feed sampling, ingredient review, and comparison of clinical signs across groups receiving different feed batches. ## Management-Related Causes ### Environmental Stress Heat stress is a well-recognized cause of loose feces in growing pigs. Pigs have limited sweat gland function and rely on evaporative cooling through the respiratory tract. Under heat stress, water intake increases substantially, and fecal water content rises. The distinction between heat-induced loose feces and true diarrhea requires assessment of hydration status, feed intake, and the presence of other clinical signs. Stocking density and pen hygiene influence diarrhea risk through fecal-oral pathogen transmission. Pigs housed at high density with poor manure management have increased exposure to enteric pathogens, and the distinction between primary nutritional diarrhea and secondary infectious diarrhea becomes blurred. A pig with mild nutritional diarrhea in a contaminated environment is at high risk of developing infectious diarrhea as a complication. ### Feed Withdrawal as a Diagnostic Test The response to feed withdrawal is a useful diagnostic discriminator. Pigs with pure nutritional or osmotic diarrhea typically show marked improvement within 24 to 48 hours of feed removal, because the osmotic load is removed. Pigs with infectious diarrhea, particularly inflammatory enteritis, show less improvement because mucosal damage and active secretion persist independent of feed intake. This test is not definitive, but it provides rapid, low-cost information that can guide further investigation. ## Diagnostic Sequence for Grower Pig Diarrhea The investigation begins with a structured herd-level assessment before any individual pig is examined. Define the population at risk by barn, room, pen, and age cohort. Determine whether the problem is endemic or explosive, whether morbidity is rising or stable, and whether mortality exceeds 1% per week. These parameters separate nutritional and management failures, which typically produce gradual onset and low mortality, from infectious outbreaks, which often present with rapid spread and higher case fatality. Establish the temporal pattern relative to feed delivery. Diarrhea that appears 12 to 36 hours after a feed change, a new ingredient load, or a mill error points toward a nutritional trigger. Diarrhea that tracks with the introduction of new pigs, or that spreads pen to pen over several days, favors an infectious agent. Water intake should be measured directly if possible, because reduced water consumption concentrates feed in the gastrointestinal tract and can produce loose feces that mimics true diarrhea. Physical examination of affected pigs provides the next layer of discrimination. Nutritional diarrhea typically leaves pigs bright, alert, and eating, with soft formed or pasty feces and no fever. Infectious diarrhea more often produces depressed pigs, reduced feed intake, fever, and feces that are watery, hemorrhagic, or contain mucus and necrotic debris. Rectal temperature above 40.0°C in a grower pig strongly supports an infectious component, although some viral enteritides cause diarrhea without significant pyrexia. ## Feed and Management Assessment A complete feed history is the single most cost-effective diagnostic step. Document the current ration formulation, ingredient sources, mixing records, and delivery dates. Compare the actual delivered ration against the formulation sheet, and retain feed samples from every suspect batch for proximate analysis, mycotoxin screening, and electrolyte quantification. Salt, calcium, and fiber levels are the most frequently implicated formulation errors in grower diarrhea. Excess salt produces osmotic diarrhea with polydipsia, while excessive calcium can precipitate phosphate and create a relative phosphorus deficiency that manifests as loose feces and poor bone mineralization. Feed intake patterns deserve equal scrutiny. Check feeder adjustment, stocking density, and water-to-feed ratios. Pigs that sort feed or that have restricted access to water will consume an imbalanced diet even when the formulation is correct. Verify that water flow rates meet the manufacturer's recommendations for the pig size and that drinker height matches the average shoulder height of the group. A water flow rate below the recommended threshold for grower pigs reduces intake and alters the osmotic environment of the large intestine. Environmental parameters should be recorded at pen level, not barn level. Floor temperature, draft exposure, and humidity vary substantially within a single room. Cold stress increases feed intake to maintain body temperature, and the excess passes through the gut more rapidly, producing loose feces. Heat stress reduces water intake relative to feed and concentrates ingesta. Both conditions can produce diarrhea that resolves when the thermal environment is corrected. ## Laboratory Testing Strategy Select laboratory tests based on the herd-level pattern, not on individual pig presentation. For acute outbreaks with fever, depression, or blood in feces, submit fresh fecal samples from at least five affected pigs in the early stages of disease. Bacterial culture for Salmonella species and Brachyspira species requires selective media and should be requested specifically. Viral diagnostics, including PCR for porcine epidemic diarrhea virus and transmissible gastroenteritis virus, are appropriate when the clinical picture includes watery diarrhea with rapid spread, though these agents are more common in nursery pigs than in grow-finish animals. For chronic or low-grade diarrhea, fecal flotation and direct smear provide information on parasite burden, particularly for coccidia and whipworms. A quantitative fecal egg count distinguishes clinically relevant burdens from incidental findings. Histopathology from a freshly euthanized, untreated pig is the most definitive test when infectious causes are suspected but routine diagnostics are negative. Collect sections from multiple gut sites, including duodenum, jejunum, ileum, cecum, and colon, because lesions may be segmental. Feed analysis is indicated when nutritional causes are suspected. Submit samples for proximate analysis, mineral profile, and mycotoxin panel. Compare results to the formulation specifications and to published nutrient requirements for the relevant weight range. A discrepancy in crude protein, fiber, or calcium of more than 10% from specification warrants investigation of the mill or ingredient supplier. ## Differential Prioritization Framework The following framework prioritizes differentials based on clinical presentation and herd parameters. It is intended to guide test selection and to prevent reflexive antimicrobial use before nutritional and management causes are excluded. | Clinical Pattern | Onset | Fever | Fecal Character | Priority Differentials | First-Line Diagnostics | |---|---|---|---|---|---| | Post-feed-change diarrhea | 12 to 36 h after ration change | Absent | Soft, pasty, voluminous | Formulation error, ingredient change, salt excess | Feed analysis, ration review | | Cold-stress diarrhea | Seasonal, drafty pens | Absent | Soft, loose | Environmental cold stress, increased intake | Pen-level temperature, airflow mapping | | Acute watery outbreak | 24 to 72 h, rapid spread | Variable | Watery, projectile | Viral enteritis, Salmonella, water contamination | PCR panel, bacterial culture, water testing | | Hemorrhagic diarrhea | Acute, individual pigs | Present | Blood, mucus | Swine dysentery, Salmonella, proliferative enteropathy | Fecal culture, PCR for Brachyspira and Lawsonia | | Chronic low-grade diarrhea | Weeks, stable morbidity | Absent | Soft, variable | Parasitism, mild nutritional imbalance, subclinical ileitis | Fecal egg count, feed analysis, serology | The framework changes with production system. In continuous-flow facilities, infectious causes are more likely to persist and to present as endemic disease with lower morbidity but constant shedding. In all-in/all-out systems, nutritional and management causes become relatively more important because the pathogen load is reduced between groups. Outdoor production introduces soil-borne parasites and environmental contaminants that are uncommon in slatted indoor systems. ## Documentation and Monitoring Record every case with a standardized form that captures the date, pen location, weight range, feed batch number, water source, and clinical findings. Photograph fecal consistency using a standardized scoring chart so that different observers and different visits can be compared reliably. Track the response to any intervention, including feed withdrawal, ration correction, or environmental adjustment, at 24, 48, and 72 hours. A rapid response to feed withdrawal supports a nutritional or management cause, while persistence of diarrhea despite feed removal favors an infectious etiology. Monitor production parameters beyond the affected pens. Average daily gain, feed conversion, and culling rates in the affected cohort provide the economic context for the outbreak and help determine whether intervention is justified. Compare these values to the previous group in the same facility and to breed averages. A 5% reduction in average daily gain over a two-week period may justify diagnostic expenditure even when mortality is negligible. Water quality testing is an underused diagnostic step. Collect samples from the drinker, not the header tank, and submit for total bacterial count, coliform count, and mineral analysis. High iron or sulfate content in well water produces osmotic diarrhea that is easily mistaken for an infectious cause. Nitrate contamination above the recommended threshold for swine can cause diarrhea and poor performance without other clinical signs. Document the diagnostic plan and its rationale in the herd health record. Note which differentials were excluded, which tests were run, and which remain unresolved. This record becomes the baseline for the next outbreak and prevents repetition of the same diagnostic sequence. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific guidance on sample collection and interpretation that can be referenced when building the herd protocol. National surveillance programs and reporting requirements, where applicable, are described by the [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease) and by [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/), and these should be consulted when an infectious cause is confirmed or suspected. ## Recognized Complications and Failure Modes The most consequential failure in grower pig diarrhea workups is misclassifying an infectious outbreak as a nutritional problem. This error typically follows a partial response to feed correction. A diet change may reduce osmotic diarrhea while an underlying enteric infection continues to transmit, producing a misleading impression that the problem has been solved. Detect this pattern by tracking group-level response over 48 to 72 hours instead of individual pig response. Nutritional diarrhea usually improves within two to three feeding cycles after the offending ingredient or intake pattern is corrected. Infectious diarrhea may transiently improve but recurs as new cases appear in previously unaffected pens. A second failure mode is overinterpreting a single diagnostic test. Fecal PCR panels detect nucleic acid from organizms that may be commensals or pass-through pathogens. Detection of *Brachyspira* or *Lawsonia* DNA does not confirm causation unless histopathology or quantitative load data support clinical relevance. Conversely, negative PCR results do not exclude infection if samples were collected late in the disease course or after antimicrobial exposure. Pair molecular testing with gross necropsy and histopathology on acutely affected, untreated pigs. A third failure mode is ignoring water delivery as a vector. Water medication lines, drinker biofilm, and contaminated water sources can perpetuate enteric disease while feed-based interventions proceed. Check water flow rates, drinker function, and water quality early in the investigation. A pen-level reduction in water intake can also be the first indicator of systemic illness instead of a primary cause of diarrhea. | Observation | Likely cause | Discriminating check | |---|---|---| | Diarrhea improves after feed change, then recurs in new pens | Concurrent infectious agent masked by nutritional correction | Repeat fecal sampling from new cases, histopathology from untreated pigs | | PCR positive for enteric pathogen but no lesions at necropsy | Pass-through organizm or sample artifact | Quantitative PCR, histopathology, and clinical correlation | | Diarrhea persists despite clean feed and stable environment | Water-borne contamination or undiagnosed systemic disease | Water culture, drinker inspection, serum biochemistry | | Single pen affected, adjacent pens normal | Localized management failure, drinker malfunction, or early index case | Pen-level feed and water audit, movement records | ## Common Diagnostic Errors and Corrections Less experienced clinicians often attribute diarrhea to a single cause and stop investigating once one abnormality is found. Grower pig diarrhea is frequently multifactorial. A diet marginally high in soluble fiber and a concurrent mild *Lawsonia* infection can produce clinical disease where neither factor alone would. Correct this by maintaining a problem list and testing each hypothesis independently. A second common error is relying on visual assessment of fecal consistency without objective scoring. Fecal consistency scores vary between observers and across barns. Standardize scoring with a written scale and have the same observer assess pens over time. This reduces noise and improves detection of true change. A third error is sampling the wrong pigs. Chronically affected, stunted pigs may carry secondary infections or have irreversible intestinal damage that obscures the primary etiology. Sample acutely affected pigs that have been sick for less than 24 to 48 hours and have not been treated. Collect multiple samples from different pens and different age cohorts to capture the range of clinical presentation. A fourth error is neglecting to rule out systemic disease presenting as diarrhea. Septicemia, salt poisoning, and hepatic or renal failure can cause loose feces in growing pigs. A complete physical examination, including hydration status, body temperature, and neurologic assessment, should precede any feed-focused investigation. ## Evidence Limitations and Areas of Expert Disagreement The evidence base for grower pig diarrhea is uneven. Much of the published literature on diarrheagenic *Escherichia coli* derives from human medicine, where pathotypes such as enterotoxigenic and enteropathogenic strains are well characterized [Nataro and Kaper, diarrheagenic *Escherichia coli* review](https://pubmed.ncbi.nlm.nih.gov/9457432/). The relevance of these pathotypes to porcine disease is established for some strains, such as enterotoxigenic *E. coli* causing post-weaning colibacillosis, but extrapolation from human data requires caution. Porcine-specific challenge models and field studies remain the more reliable reference for clinical decision-making. Expert opinion diverges on the threshold for antimicrobial intervention in suspected infectious diarrhea. Some clinicians advocate immediate metaphylaxis when *Lawsonia* or *Brachyspira* is suspected, while others prefer confirmatory diagnosis before treatment. This disagreement reflects the absence of rapid, sensitive point-of-care tests for these pathogens and the economic pressure to act quickly in a group setting. The prudent approach is to establish a working diagnosis, initiate supportive care, and treat only when clinical deterioration or confirmed pathogen identification justifies antimicrobial use. There is also limited consensus on the role of specific dietary components in non-infectious diarrhea. Fiber type and fermentability, protein source and concentration, and feed processing methods all influence fecal consistency, but controlled studies are sparse and results vary across production systems. Regional differences in ingredient availability and feed mill practices further complicate generalization. The [FAO animal production guidance](https://www.fao.org/animal-production/en/) and [MSD Veterinary Manual](https://www.msdvetmanual.com/) provide practical frameworks, but neither resolves the underlying evidence gaps. ## Escalation and Referral Criteria Referral or specialist consultation is warranted when the diarrhea outbreak is severe, rapidly progressive, or unresponsive to standard diagnostic and management interventions. Specific triggers include high morbidity with rising mortality, neurologic signs in affected pigs, or diarrhea that persists beyond 7 to 10 days despite feed and environmental correction. A veterinary diagnostic laboratory should be involved when histopathology, bacterial culture, or specialized molecular testing is required to distinguish between pathogens with similar clinical presentations. Regulatory reporting obligations vary by jurisdiction and by the pathogens involved. Some enteric pathogens of swine are reportable to national or international authorities. The [WOAH terrestrial animal health code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) defines notification requirements for listed diseases, and the [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease) portal provides national program details for producers and veterinarians in the United States. Clinicians should confirm local reporting requirements before initiating a workup, particularly when clinical signs suggest a foreign animal disease or a pathogen with trade implications. Consultation with a swine nutritionist is appropriate when feed formulation errors are suspected but cannot be identified from feed records alone. A nutritionist can perform a complete ration analysis, evaluate ingredient quality, and model the impact of formulation changes on intestinal health. Similarly, an agricultural engineer may be needed to assess ventilation, water delivery, or manure handling systems when environmental factors are implicated. ## Frequently Asked Questions ### How do I distinguish nutritional diarrhea from an early infectious outbreak when only a few pigs are affected? Examine the distribution pattern. Nutritional diarrhea typically affects a pen or room uniformly within 12 to 48 hours of a feed change, with severity tracking feed intake. Infectious disease usually spreads progressively from one pen to adjacent pens over several days. Assess whether affected pigs are febrile, lethargic, or showing signs beyond the gastrointestinal tract. Nutritional cases rarely cause fever or marked depression. Collect fecal samples from untreated, acutely affected pigs for pathogen testing while you review feed records. If clinical signs resolve within 24 to 48 hours of correcting the feed issue, nutritional causation is supported. Persistence or spread despite feed correction warrants laboratory investigation for infectious agents. ### What is the minimum diagnostic workup when the farm budget is severely limited? Prioritize postmortem examination of one or two untreated, acutely affected pigs over laboratory testing. Gross lesions help separate enteritis from maldigestion. Collect fixed and fresh intestinal samples, plus fecal swabs, and hold them pending gross findings. Submit samples for bacterial culture and histopathology only when gross lesions suggest an infectious process. Review feed tags, mycotoxin screens, and water quality records before spending on molecular diagnostics. A thorough feed assessment costs nothing and frequently identifies the cause. When laboratory funds allow only one test, bacterial culture of ileum and colon from a fresh carcass provides the broadest return for grower pigs. Consult [MSD Veterinary Manual diagnostic guidance](https://www.msdvetmanual.com/) for sample handling protocols. ### How should I interpret a positive pathogen result when clinical signs point equally to a nutritional cause? A positive test does not prove causation. Many enteric pathogens circulate subclinically in grower herds, and concurrent nutritional stress can trigger clinical disease. Interpret laboratory results alongside lesion severity, pathogen load, and population-level patterns. Quantitative PCR results should be assessed against the laboratory's reference ranges for clinically significant shedding. If lesions are mild and feed errors are confirmed, treat the feed problem first and monitor response. Re-test only if diarrhea persists. When lesions are severe and the pathogen is present in high numbers, infectious causation is more likely even with a concurrent feed issue. The [diarrheagenic Escherichia coli categories described by Nataro and Kaper](https://pubmed.ncbi.nlm.nih.gov/9457432/) illustrate how different pathogenic mechanisms produce distinct clinical and pathological presentations. ### What records should I maintain to make future diarrhea outbreaks easier to diagnose? Maintain a feed event log that records each diet change, ingredient lot number, feed mill delivery date, and any feed intake anomalies. Track water flow rates and quality test results per barn. Record daily diarrhea prevalence by pen, including onset date, affected age group, and response to interventions. Keep postmortem findings and laboratory results in a searchable format that links to the relevant feed batch. Photograph gross lesions and feed tags for later reference. Standardized records allow you to identify recurring patterns, such as diarrhea consistently appearing three days after a specific ingredient substitution. [USDA APHIS animal health information](https://www.aphis.usda.gov/livestock-poultry-disease) provides guidance on disease monitoring and reporting frameworks that support outbreak investigation. ### How do I explain a nutritional diarrhea diagnosis to a producer who expects an infectious cause and wants antibiotics? Frame the diagnosis in terms of economics and pig welfare. Explain that correcting the feed problem resolves the diarrhea without withdrawal periods or treatment costs. Show the producer the feed records and the temporal association with the diet change. Describe how antibiotics would not address the underlying cause and could select for resistance in the herd's commensal flora. If the producer remains concerned about infectious disease, propose a limited diagnostic confirmation, such as culture of one or two affected pigs, to document the absence of a primary pathogen. The [AVMA practice resources](https://www.avma.org/resources-tools) offer communication frameworks for discussing diagnostic reasoning and antimicrobial stewardship with clients. ### When should I suspect a water-associated cause instead of a feed or infectious cause? Suspect water when diarrhea is uniform across all pigs drinking from one water source but absent in pigs on a different source, or when onset coincides with a water system change. Check water flow rates, since low pressure reduces intake and concentrates electrolytes. Test for sulfate, nitrate, iron, and bacterial contamination. High sulfate causes osmotic diarrhea that mimics nutritional disease. Water medication or mineral supplements delivered through the system can also cause diarrhea if the dosing pump malfunctions. Review whether diarrhea resolves when pigs are offered an alternative water source. Water quality problems often coexist with feed issues, so assess both systems before concluding that one is responsible. ## 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 - [Diarrheagenic Escherichia coli.](https://pubmed.ncbi.nlm.nih.gov/9457432/). 1998. - [Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic.](https://pubmed.ncbi.nlm.nih.gov/20610826/). 2010. - [Escherichia coli ST131, an intriguing clonal group.](https://pubmed.ncbi.nlm.nih.gov/24982321/). 2014. - [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. - [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association. - [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/). WOAH. ## Related Articles - [Differential Diagnosis of Anemia in Swine: Iron Deficiency vs. Infectious Causes](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-anemia-swine-iron-deficiency-infectious) - [Differential Diagnosis of Sudden Death in Growing Pigs](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-sudden-death-growing-pigs) - [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 Abortion in Dairy Cattle: Infectious and Non-Infectious Causes](/knowledge/veterinary-medicine/food-animal-medicine/differential-diagnosis-abortion-dairy-cattle-infectious-noninfectious) - [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) > 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.