# [Dairy Cow Culling Decisions](/knowledge/veterinary-medicine/food-animal-medicine/dairy-herd-culling-decisions-data-driven-approaches) and Records ## Key Takeaways - Dairy cow culling decisions are multifaceted, integrating health status (e.g., chronic mastitis, lameness, Johne's disease), production metrics (milk yield relative to herd average, somatic cell count), fertility performance (days open, calving interval), and welfare indicators (body condition score, mobility score). - A structured, record-based culling framework is essential, utilizing data from Dairy Herd Improvement (DHI) records, veterinary diagnoses, and herd health assessments to ensure consistent and justifiable decisions aligned with herd goals. - Economic considerations involve a dynamic comparison of a cow's projected future net revenue against the cost and potential of a replacement heifer, accounting for feed costs, milk prices, and cull cow values. - Animal welfare serves as a critical constraint, mandating the culling of cows with chronic, painful conditions that cannot be effectively managed, and ensuring fitness for transport as per WOAH standards. - Comprehensive documentation of culling decisions, including cow ID, date, reasons, supporting evidence, and disposition method, is vital for auditing herd performance, regulatory compliance, and identifying management gaps. - Facility design, nutrition, and production stage significantly influence culling, with poor housing contributing to lameness, inadequate nutrition leading to metabolic diseases, and stage-specific thresholds for milk yield and somatic cell count guiding decisions. --- Dairy cow culling is a routine but consequential herd management decision that directly affects farm profitability, herd genetics, and animal welfare. Culling should not be treated as an isolated event but as the endpoint of a documented evaluation process that weighs health status, production records, fertility performance, welfare indicators, replacement heifer availability, and prevailing market conditions for cull cows. A structured, record-based culling framework allows producers and veterinarians to make consistent, justifiable decisions that align with herd goals and reduce the risk of sending compromised animals through the marketing chain. ## At a Glance | Decision Domain | Key Factors in Culling Evaluation | Information Source | |----------------|----------------------------------|-------------------| | Health | Chronic mastitis, lameness, injury, metabolic disease, Johne's disease | Treatment records, veterinary diagnoses, [Merck Veterinary Manual](https://www.merckvetmanual.com/) protocols | | Production | Milk yield relative to herd average, lactation persistency, [somatic cell](/blog/guides/somatic-cell) count | Dairy Herd Improvement (DHI) records, monthly test data | | Fertility | Days open, number of services, calving interval, pregnancy status | Breeding records, palpation or ultrasound reports | | Welfare | Body condition score, mobility score, udder conformation, lesions | Herd health assessments, [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) welfare standards | | Replacement | Number and quality of available heifers, genetic merit, heifer health status | Replacement inventory records, genomic evaluations | | Market Context | Cull cow price, beef market trends, transport distance to market or abattoir | USDA market reports, livestock auction data | ## System Context for Culling Decisions ### Herd Dynamics and Economic Pressure Culling decisions occur within a complex system where replacement heifers enter the milking herd at a predictable rate and cull cows exit through sale or on-farm euthanasia. The economic calculus involves comparing the future net revenue expected from a current cow against the expected net revenue from a replacement heifer. This comparison must account for the cow's current milk production, projected lactation performance, reproductive potential, and the probability of future health events. The replacement heifer carries her own acquisition cost, rearing expense, and probability of successful transition into the milking herd. Published models of culling economics treat this as a dynamic programming problem where the optimal decision changes with the cow's age, lactation stage, and current market prices. The economics of dairy cow culling are not static, they shift with feed costs, milk prices, and cull cow values in ways that require regular recalculation. ### Welfare as a Bounded Constraint Animal welfare considerations place a hard boundary on culling decisions. A cow with a chronic, painful condition that cannot be effectively treated or managed may be culled even if her production or reproductive records would otherwise justify retention. This principle is embedded in the [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) standards for transport and slaughter, which require that animals be fit for the intended journey. The [USDA APHIS Livestock and Poultry Disease](https://www.aphis.usda.gov/livestock-poultry-disease) program monitors compliance with fitness-for-transport regulations, meaning that a culling decision must include an assessment of whether the cow can be safely transported to market or an abattoir without undue suffering. Evidence from field studies indicates that a proportion of cows placed on the culling list are already in compromised condition at the time the decision is made, but it is not always clear whether deterioration occurs before or after the cow leaves the farm. This uncertainty underscores the need for objective, timed assessments at the point of culling. ## Planning Decisions and Core Management Framework ### Establishing Culling Criteria A documented culling policy should specify the thresholds that trigger a culling evaluation for each decision domain. These thresholds are farm-specific and should be set by the herd veterinarian in consultation with the producer. For health-based culling, common criteria include a diagnosed chronic condition (e.g., Johne's disease, recurrent mastitis in the same quarter) or a condition expected to produce pain or suffering that cannot be resolved within a defined treatment window. [PubMed record 42431443](https://pubmed.ncbi.nlm.nih.gov/42431443/) and [PubMed record 42357793](https://pubmed.ncbi.nlm.nih.gov/42357793/) address specific health conditions that influence culling timing, though the exact thresholds remain a matter of veterinary judgment applied to individual cases. For production-based culling, the threshold is typically expressed as a percentage of the herd average milk yield. For example, a cow producing below 70 percent of the herd average in early lactation may be flagged for evaluation. Fertility-based culling often uses days open, with common thresholds ranging from 200 to 250 days open depending on the herd's breeding program and acceptable calving interval. ### Documentation and Record Keeping Every culling decision should be recorded in a standardized format that includes the cow identification number, date of decision, primary and secondary reasons for culling, supporting evidence (e.g., [somatic cell](/blog/guides/somatic-cell) count trends, treatment records, reproductive history), and the method of disposition (sale at auction, direct slaughter, on-farm euthanasia). This documentation serves multiple purposes. It allows the farm to audit culling patterns over time and identify trends that may indicate underlying herd health problems or management gaps. It supports compliance with animal welfare and [food safety](/knowledge/bacteria/livestock-bacteria/cooking-chicken-bacteria-prevention) regulations. And it provides a defensible record in the event of an inspection or a complaint. The [USDA National Animal Health Monitoring System](https://www.aphis.usda.gov/livestock-poultry-disease/nahms) includes culling data collection as part of its national dairy studies, demonstrating the value of standardized records at the industry level. ### Timing and Execution of Culling Once a decision is made, the timing of the cull cow's removal from the farm should be planned to minimize stress and risk of deterioration. Cows that are merely low-producing or open should be culled in a timely manner consistent with market conditions. Cows with welfare-compromising conditions should be culled immediately and, if necessary, euthanized on farm instead of subjected to transport. The [FAO Animal Production and Health](https://www.fao.org/animal-production/en/) guidelines emphasize that the interval between culling decision and removal should be as short as feasible, particularly for animals in poor body condition or with mobility problems. The risk of deterioration during transport and lairage is well documented, and a rapid, direct movement from farm to an approved abattoir is the preferred pathway for compromised animals. ## Facilities and Environment Housing and facility design directly influence the frequency and timing of culling decisions. Poor stall comfort, inadequate bedding, and abrasive flooring contribute to hoof lesions and lameness, a leading reason for involuntary culling. The [Merck Veterinary Manual](https://www.merckvetmanual.com/) notes that persistent lameness often becomes refractory to treatment, prompting removal. Cross-ventilated freestall barns with deep-bedded stalls and rubber flooring reduce injury and support longer productive life. Conversely, confinement systems with concrete slats and limited exercise increase culling for locomotion failure. Environmental factors such as heat stress and overcrowding also elevate culling risk by suppressing feed intake, reducing fertility, and increasing disease transmission. Deterioration during transport and marketing is well documented, a 2020 study tracked cull cows from farm to abattoir and found that body condition, lameness, and udder condition often worsened after leaving the farm, especially when cows spent extended periods at livestock markets ([Semantic Scholar, 2020](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e)). Facilities that allow timely, direct shipment to slaughter minimize this welfare decline and preserve carcass value. ## Nutrition and Water Nutritional status is a key determinant of culling decisions, particularly for metabolic disease and body condition score (BCS). Chronic subclinical ketosis, hypocalcemia, and ruminal acidosis weaken cows and increase the likelihood of removal. Nutrition-driven culling often occurs in early lactation when energy balance is most negative. The [FAO Animal Production and Health](https://www.fao.org/animal-production/en/) resources emphasize that feeding strategies must match production demands to avoid excessive culling for metabolic failure. Water availability and quality also affect intake and health, restricted or contaminated water predisposes cows to dehydration and reduced feed efficiency, accelerating culling for poor performance or debilitation. In the 2020 study of cull cows, a substantial proportion arrived at abattoir with low BCS, and researchers could not determine whether this condition originated on farm or developed during marketing ([Semantic Scholar, 2020](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e)). Routine BCS assessment and body weight monitoring, combined with feed analysis, enable early identification of cows that are unlikely to recover productivity and may be best culled before condition deteriorates further. ## Production-Stage Decisions Culling decisions are strongly stage-dependent. In early lactation, culling is often forced due to severe disease (mastitis, metritis, displaced abomasum) or acute injury. Mid,lactation culling is more frequently voluntary, based on projected profitability relative to replacement heifers. Late lactation and dry period culling decisions involve forecast of future productivity, calving interval, and postpartum health. The economics of dairy cow culling have been modeled to assess optimal replacement timing. One 1994 paper established basic principles using net present value analysis and demonstrated that the optimal culling decision depends on expected milk yield, reproductive status, and future health costs ([Semantic Scholar, 1994](https://www.semanticscholar.org/paper/7c21164499b68b09fa008e83c460d42ec472c66e)). A companion simulation study evaluated herd management strategies and confirmed that delaying culling of low producers or cows with extended calving intervals reduces herd profitability ([Semantic Scholar, 1994](https://www.semanticscholar.org/paper/22bdbbc8b09b8ed37a52bfefbc29f3b2b67c7fd3)). Producers should re,evaluate culling triggers at each production stage, using current performance data instead of historical expectations. The 1998 review on dairy cow culling decisions underscores that the decision to cull is often postponed until a cow’s low production or clinical disease becomes economically obvious, missing opportunities for earlier, more profitable removal ([Semantic Scholar, 1998](https://www.semanticscholar.org/paper/c56a134b682792cc31186f592ae4fed5f1d20b15)). Incorporating stage,specific thresholds for milk yield, somatic cell count, and body condition improves objectivity. ## Records Systematic record-keeping is essential for evidence,based culling. A 1993 paper on techniques involved in making culling decisions highlighted the need for accurate individual cow data on milk yield, reproduction, health events, and pedigree ([Semantic Scholar, 1993](https://www.semanticscholar.org/paper/f91f0065f1efd244eca25bc9e07482b229fd3b96)). Without reliable records, culling becomes reactive and emotional, often retaining low,profit cows while culling high,potential animals prematurely. Records should include calving dates, breeding results, disease treatments, and daily or monthly milk weights. Integration with Dairy Herd Improvement (DHI) or on,farm software allows calculation of projected net returns and replacement cost. The [USDA National Animal Health Monitoring System (NAHMS)](https://www.aphis.usda.gov/livestock-poultry-disease/nahms) provides national benchmarks that producers can use to evaluate their culling rates against regional averages. Records also document compliance with withdrawal periods for medications, which is critical for food safety and regulatory adherence. When a cow is placed on a culling list, the decision date, reason code, and current health and production status should be recorded. This historical data helps identify failure patterns and guides future management changes. ## Welfare Welfare considerations must be integrated into every culling decision. The [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) includes standards for transport and slaughter of compromised animals. Cows that are non,ambulatory, severely emaciated, or have open fractures should not be transported, they require on,farm euthanasia. The 2020 study noted that many cull cows arrive at abattoir with conditions that could have been managed on farm to reduce suffering ([Semantic Scholar, 2020](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e)). Providing producers with feedback on the condition of their cull cows at the abattoir improved subsequent culling decisions, but the study found that simply providing information did not necessarily reduce the proportion of compromised cows sent to market, suggesting that economic pressures and infrastructure remain significant barriers. Escalation to veterinary oversight is warranted when culling decisions involve recumbent or chronically diseased cows. The [USDA APHIS Livestock and Poultry Disease](https://www.aphis.usda.gov/livestock-poultry-disease) program monitors transport violations and can intervene in cases of neglect. On,farm euthanasia methods must be humane, verified by a veterinarian, and performed according to AVMA or similar guidelines. ## Worker and Food Safety Worker safety is compromised when handling aggressive, injured, or diseased cows. Culling decisions should consider whether a cow poses a risk to handlers during milking, treatment, or loading. Personnel training in low,stress handling reduces injury. Food safety is directly affected by culling decisions. Cows treated with antibiotics must meet meat withdrawal periods before slaughter. The [Merck Veterinary Manual](https://www.merckvetmanual.com/) outlines the risk of violative residues in cull cows. Monitoring protocols such as milk screening tests and tissue residue testing help ensure compliance. Mastitis treatment records must be reviewed before a cow is shipped for slaughter, failure to do so can lead to carcass condemnation and regulatory penalties. The 2003 review of mastitis economics noted that culling chronically infected cows reduces bulk tank somatic cell count and improves milk quality premiums, thus offsetting some replacement costs ([Scopus, 2003](https://api.elsevier.com/content/abstract/scopus_id/0242608441)). Veterinarians should be consulted when extended withdrawal periods are needed due to off,label drug use, and a written food safety plan should document all decisions. ## Failure Patterns Analysis of culling failure patterns reveals that three categories dominate: reproduction (low fertility, prolonged calving interval), production (low milk yield, high somatic cell count), and health (mastitis, lameness, metabolic disease). Published studies, including those provided by [PubMed record 42357793](https://pubmed.ncbi.nlm.nih.gov/42357793/) and [PubMed record 42215337](https://pubmed.ncbi.nlm.nih.gov/42215337/), report that these categories account for the majority of involuntary culling in dairy herds globally. Patterns shift with herd management,for example, herds that aggressively treat clinical mastitis may have lower culling for mastitis but higher for chronic high somatic cell count. Recognition of recurring failure patterns can prompt management changes: if lameness culling rises, evaluate hoof,trimming schedules and stall comfort, if infertility culling increases, review heat detection and bull fertility. The 1998 culling decisions review emphasized that failure patterns are not static, they change with herd expansion, genetics, and market conditions ([Semantic Scholar, 1998](https://www.semanticscholar.org/paper/c56a134b682792cc31186f592ae4fed5f1d20b15)). Regular analysis of culling reasons, ideally by quarter, provides feedback for improvement. ## Practical Monitoring Practical monitoring of culling decisions involves tracking key performance indicators. Monthly culling rate (involuntary and voluntary), reasons for removal, and the proportion of cows leaving underweight or in poor condition should be calculated. The [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) recommends recording the condition of animals at departure. A simple scoring system for body condition, lameness, and udder health used at the time of culling can be compared with abattoir feedback (if available). Herd veterinarians should review culling records at least quarterly. The economic simulation studies from 1994 demonstrated that herds using dynamic culling strategies (adjusting thresholds based on replacement costs and milk prices) outperformed those using static culling rules ([Semantic Scholar, 1994](https://www.semanticscholar.org/paper/22bdbbc8b09b8ed37a52bfefbc29f3b2b67c7fd3)). Monitoring also includes tracking the age distribution of the herd, a rising proportion of first,lactation cows indicates increased premature culling, which may signal underlying management issues. Record,keeping software can generate alerts when a cow falls below a production or reproduction threshold. However, no single threshold fits all operations, adjustments for genetics, feed costs, and heifer availability are necessary. Professional escalation to a veterinarian or extension specialist is recommended when culling rate exceeds 35% annually or when injury or welfare concerns become frequent. ## Health Observation and Biosecurity in Culling Decisions Systematic health observation underlies defensible culling decisions. Daily inspection of body condition, locomotion, udder health, and general demeanor allows early detection of conditions that may justify removal. [Merck Veterinary Manual](https://www.merckvetmanual.com/) describes standardized scoring systems for body condition and lameness that provide objective thresholds for decision making. Regular observation also identifies chronic or recurrent disease that fails to respond to treatment, a common reason to cull. Biosecurity considerations enter the culling process in two ways. First, culling itself is a biosecurity tool: removing animals that shed pathogens reduces within-herd disease pressure. [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) outlines principles for managing infected and at-risk animals to prevent disease spread. Second, the movement of cull cows from farm to market or abattoir creates biosecurity risk if animals are transported while still infectious. [USDA APHIS Livestock and Poultry Disease](https://www.aphis.usda.gov/livestock-poultry-disease) provides guidelines for interstate movement of cattle that apply to cull animals. ### Diagnostic Confirmation and Veterinary Escalation Culling decisions benefit from diagnostic confirmation when the cause of impaired health or production is unclear. [PubMed record 42215337](https://pubmed.ncbi.nlm.nih.gov/42215337/) examined diagnostic approaches in dairy herds and underscored that laboratory testing can differentiate between treatable conditions and irreversible pathology. [PubMed record 41938792](https://pubmed.ncbi.nlm.nih.gov/41938792/) specifically addressed mastitis diagnosis and its role in culling, noting that chronic subclinical mastitis often warrants removal if somatic cell count remains elevated despite therapy. Veterinary escalation is indicated when disease is suspected but not confirmed, when multiple animals present similar signs, or when the economic analysis of retention versus replacement is complex. [PubMed record 42018091](https://pubmed.ncbi.nlm.nih.gov/42018091/) discussed the integration of veterinary advice into culling protocols to reduce premature removal and to avoid retaining animals with poor prognosis. [Techniques involved in making dairy cow culling decisions](https://www.semanticscholar.org/paper/f91f0065f1efd244eca25bc9e07482b229fd3b96) (1993) emphasized that farmer judgment alone often underestimates the economic cost of delayed culling, supporting a team approach. ### Uncertainty in Culling Decisions Uncertainty pervades culling decisions. The future productive life of a cow cannot be predicted with certainty, and economic models rely on assumptions about milk price, replacement cost, and health outcomes. [The economics of dairy cow culling decisions. 1. Basic principles and modelling approach](https://www.semanticscholar.org/paper/7c21164499b68b09fa008e83c460d42ec472c66e) (1994) described how dynamic programming accounts for uncertainty by assigning probabilities to future states. [The economics of dairy cow culling decisions. 4. Economic simulation of herd management strategies](https://www.semanticscholar.org/paper/22bdbbc8b09b8ed37a52bfefbc29f3b2b67c7fd3) (1994) showed that optimal culling strategies change with market conditions, reinforcing the need to re-evaluate decisions regularly. [Production effects related to mastitis and mastitis economics in dairy cattle herds](https://api.elsevier.com/content/abstract/scopus_id/0242608441) (2003-09-01) highlighted that the cost of mastitis is often underestimated, introducing further uncertainty into retention calculations. ### Sustainability and Animal Welfare Sustainability encompasses economic viability, environmental impact, and animal welfare. Culling decisions affect all three. Removing chronically lame or emaciated cows improves herd welfare records and reduces the environmental footprint of maintaining unproductive animals. [Management of cull dairy cows: Culling decisions, duration of transport, and effect on cow condition](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e) (2020) documented that a substantial proportion of cull cows arrive at abattoirs in compromised condition, raising welfare concerns. The study suggested that earlier culling and more direct transport routes could reduce deterioration. Producers should coordinate with buyers and transporters to minimize stress and injury during marketing. Sustainability also means avoiding premature culling that wastes genetic potential. [Dairy cow-culling decisions](https://www.semanticscholar.org/paper/c56a134b682792cc31186f592ae4fed5f1d20b15) (1998) argued that balancing production, reproduction, and health records over multiple lactations yields more sustainable herd turnover than reacting to single events. ## Frequently Asked Questions 1. **What health conditions most commonly lead to culling in dairy cows?** Mastitis, lameness, infertility, and metabolic disorders are leading health-related reasons for culling. [Merck Veterinary Manual](https://www.merckvetmanual.com/) provides diagnostic criteria for each condition. 2. **How should lameness be assessed before culling?** Locomotion scoring using a 1,5 scale, with scores 4 and 5 indicating severe lameness that may warrant immediate culling. [Management of cull dairy cows](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e) (2020) found that lameness prevalence increases during transport. 3. **What role does biosecurity play in the culling process?** Culling removes disease reservoirs. [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) advises that cull animals be segregated from the herd before transport to prevent pathogen spread. 4. **When should a veterinarian be involved in a culling decision?** When disease diagnosis is unclear, when herd-level patterns of illness appear, or when the economic analysis requires expert input. [PubMed record 42357793](https://pubmed.ncbi.nlm.nih.gov/42357793/) discusses the value of veterinary input. 5. **How does culling affect herd sustainability?** Timely culling of unproductive or unhealthy animals reduces resource waste and improves average herd performance. Poor culling decisions can lead to genetic loss or prolonged disease transmission. 6. **What is the biggest source of uncertainty when deciding to cull?** Predicting future milk yield and health of a retained cow. [The economics of dairy cow culling decisions. 1](https://www.semanticscholar.org/paper/7c21164499b68b09fa008e83c460d42ec472c66e) (1994) outlines how probabilistic models address this. 7. **Can culling decisions be improved through record keeping?** Yes. Records of production, reproduction, health treatments, and body condition scores allow objective comparison of individual cows. [PubMed record 42431443](https://pubmed.ncbi.nlm.nih.gov/42431443/) links record accuracy to culling efficiency. 8. **What happens to cull cows after they leave the farm?** Most are sold through livestock markets or directly to abattoirs. [Management of cull dairy cows](https://www.semanticscholar.org/paper/00c4ca6aaa96237a3949e39e2c57ab472df01d8e) (2020) found that condition often deteriorates during transport, emphasizing the need for timely marketing. ## Educational Veterinary Notice Producers are encouraged to work with their herd veterinarian to develop a written culling protocol based on health, production, and fertility records. Regular review of culling outcomes and market conditions helps refine decision rules. Veterinary guidance ensures that animal welfare is considered at every stage, from farm to transport. Maintain your records, consult your veterinarian, and make culling decisions that support both herd productivity and welfare. ## Related Farming Guides - [Dairy Cattle Farming Nutrition Housing Health Signals And Herd Management](/knowledge/animal-farming/dairy-cattle/dairy-cattle-farming-nutrition-housing-health-signals-and-herd-management) - [Transition Cow Management From Dry Off To Freshening](/knowledge/animal-farming/dairy-cattle/transition-cow-management-from-dry-off-to-freshening) - [Dairy Calf Colostrum Management](/knowledge/animal-farming/dairy-cattle/dairy-calf-colostrum-management) - [Milking Routine And Parlor Hygiene](/knowledge/animal-farming/dairy-cattle/milking-routine-and-parlor-hygiene) - [Dairy Farm Records That Drive Better Decisions](/knowledge/animal-farming/dairy-cattle/dairy-farm-records-that-drive-better-decisions) ## Related Clinical & Scientific Guides * [Evaluating Feed Additives for Dairy Cow Performance](/knowledge/animal-farming/dairy-cattle/evaluating-feed-additives-for-dairy-cow-performance) * [Dairy Barn Fire Safety: Design and Prevention Measures](/knowledge/animal-farming/dairy-cattle/dairy-barn-fire-safety-design-prevention) * [Dairy Cow Pregnancy Loss Records and Review](/knowledge/animal-farming/dairy-cattle/dairy-cow-pregnancy-loss-records-and-review) ## References and Further Reading - [FAO Animal Production and Health](https://www.fao.org/animal-production/en/) - [WOAH Terrestrial Animal Health Code](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) - [USDA APHIS Livestock and Poultry Disease](https://www.aphis.usda.gov/livestock-poultry-disease) - [Merck Veterinary Manual](https://www.merckvetmanual.com/) - [USDA National Animal Health Monitoring System](https://www.aphis.usda.gov/livestock-poultry-disease/nahms) > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.