Diagnostic Approach to Lameness in Sheep: Differentiating Footrot from Other Causes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• Ovine footrot is primarily caused by Dichelobacter nodosus, with Fusobacterium necrophorum acting as a predisposing pathogen that colonizes interdigital skin, facilitating D. nodosus invasion and subsequent hoof horn underrunning.
• Real-time PCR is the reference standard for confirming D. nodosus infection, offering superior sensitivity and specificity compared to bacterial culture, with pooled samples of five feet providing a cost-effective flock screening strategy.
• Critical differential diagnoses for lameness include Contagious Ovine Digital Dermatitis (CODD), characterized by coronary band lesions, white line disease presenting as interdigital separation, and pedal joint abscesses with localized swelling and pain.
• Ovine interdigital dermatitis, caused solely by F. necrophorum, presents as superficial interdigital inflammation without horn underrunning and does not necessitate footrot-specific interventions.
• Non-foot causes of lameness, such as brucellosis (especially in endemic regions), joint ill, septic arthritis, and traumatic injuries, must be considered during a complete physical examination to avoid misdiagnosis.
• Clinical footrot scoring systems correlate strongly with PCR detection of D. nodosus, serving as a reliable field tool for identifying infected animals, but laboratory confirmation is essential for definitive diagnosis and strain characterization.

Lameness is among the most frequent health problems presented in ovine practice, and footrot is the dominant infectious cause in most sheep-keeping regions. This article provides a structured diagnostic approach for the practicing veterinarian, covering lesion localization, clinical scoring, laboratory confirmation, and the differentiation of footrot from other foot and leg conditions. The focus is diagnostic reasoning only, treatment and control are not covered.

The reader is assumed to be a qualified veterinarian comfortable with routine ovine examination and handling. The article addresses the clinical question most commonly faced in sheep practice: when a lame sheep is presented, how does the clinician determine whether footrot is responsible, and what alternative diagnoses must be considered before committing to a footrot-specific management plan? The diagnostic logic presented here applies across production systems, though the relative frequency of differential diagnoses varies between intensive, semi-intensive, and extensive flocks.

At a Glance

Pathophysiology of Footrot

Footrot is a multifactorial, contagious disease requiring the interaction of D. nodosus with the host, the environment, and other bacteria. F. necrophorum first colonizes the interdigital skin, creating a suitable microenvironment for D. nodosus to establish infection. The virulent strains of D. nodosus produce proteases that digest the hoof horn, leading to the characteriztic underrunning lesion. The disease is highly contagious and is the main cause of lameness in sheep in many regions, as documented in recent Austrian prevalence work examining PCR detection of D. nodosus compared with clinical and bacteriological findings.

Environmental moisture and warmth are the most critical risk factors. The disease is more severe in semi-intensive and intensive farming systems, where stocking density, hygiene, and housing conditions favor transmission. A hereditary predisposition has been documented, but environmental factors determine the occurrence of foot-related lameness more strongly, as summarized in a review of aetiology, risk factors, and diagnosis of foot-related lameness in dairy sheep.

Clinical Examination and Lesion Localization

The diagnostic workup begins with observation of the sheep at rest and in motion. Lameness scoring should be performed before handling, as restraint alters gait. The clinician then examines all four feet, because footrot frequently affects multiple feet and bilateral lesions are common. The interdigital space is inspected for erythema, erosion, and odor. The sole and heel are examined for underrunning, and the coronary band is palpated for swelling and pain.

Footrot lesions are graded using clinical scoring systems that describe the progression from interdigital dermatitis to severe underrunning. These scores correlate strongly with PCR detection of D. nodosus, supporting their use as a reliable field tool. However, clinical examination identifies infected animals but cannot replace laboratory confirmation when the diagnosis is uncertain or when the distinction between virulent and benign strains matters for flock-level decisions.

Laboratory Confirmation

Real-time PCR is the reference method for confirming D. nodosus infection. Interdigital swabs are collected from affected feet, and the samples can be pooled. A pool-of-five strategy detects footrot as effectively as testing individual samples, offering a cost-effective approach for flock screening, as demonstrated in the Austrian field study on sample pooling for PCR diagnosis of footrot. Bacterial culture has a sensitivity of 75 percent compared with PCR, with 100 percent specificity, making culture useful for confirmation but inadequate for screening.

PCR also distinguishes virulent from benign strains of D. nodosus based on protease gene characteriztics. This distinction has management implications, but the diagnostic approach remains the same: clinical examination identifies suspect animals, and PCR confirms the diagnosis and characterizes the strain.

Differential Diagnosis of Foot Lesions

Contagious Ovine Digital Dermatitis

CODD is a distinct disease caused by Treponema spp. and presents with severe lameness and lesions that begin at the coronary band instead of the interdigital space. The hoof horn may be completely shed in advanced cases. CODD is often confused with severe footrot, but the lesion distribution differs. Recent research has improved evidence-based guidance on CODD diagnosis and management, and the disease is now recognized as a common cause of severe lameness in the UK. Differentiation matters because CODD responds poorly to footrot-specific control measures.

White Line Disease and Pedal Joint Abscess

White line disease presents as separation of the white line with dirt and debris packed into the defect. It is typically unilateral and affects individual animals instead of causing flock-level lameness. Pedal joint abscess presents with severe lameness, swelling of the coronary band, and a draining tract in advanced cases. Both conditions require careful hoof examination and probing to distinguish from footrot.

Ovine Interdigital Dermatitis

Ovine interdigital dermatitis is caused by F. necrophorum alone and presents as superficial interdigital inflammation without underrunning. It is often a precursor to footrot and may coexist with it. The distinction is clinically relevant because interdigital dermatitis alone does not require footrot-specific intervention.

Non-Foot Causes of Lameness

Lameness in sheep is not always foot-related. Systemic disease, including brucellosis, can present with lameness as a clinical sign. Brucellosis is a serious zoonotic bacterial disease affecting sheep and goats, and lameness is among its reported manifestations, as described in the review of brucellosis diagnostics and vaccine insights. In regions where brucellosis is endemic, lameness in a flock should prompt consideration of this diagnosis, particularly when reproductive signs are also present.

Other non-foot causes include joint ill in lambs, septic arthritis, and traumatic injuries. The diagnostic approach requires a complete physical examination, also a foot examination, to avoid missing systemic disease.

Diagnostic Algorithm and Lesion Scoring

A structured diagnostic algorithm reduces the risk of misclassification and supports consistent flock-level decisions. The sequence begins with gait assessment at rest and in motion, followed by careful foot inspection, lesion scoring, and targeted sampling when laboratory confirmation is needed.

The clinical examination can reliably identify animals infected with Dichelobacter nodosus in most cases, but PCR is required to confirm the diagnosis at the individual or flock level. In a cross-sectional study of western Austrian sheep flocks, clinical footrot scores and lameness scores correlated strongly with PCR detection of D. nodosus, yet bacterial culture showed a sensitivity of only 75% compared with PCR, despite 100% specificity. This means a negative culture does not exclude infection, and clinical scoring alone, while useful, cannot substitute for molecular confirmation when the diagnosis is uncertain or when eradication programs are being planned.

Stepwise Assessment Protocol

Begin with the animal standing undisturbed. Observe weight distribution, toe-touching, and reluctance to bear weight on a specific limb. Then move the sheep and assess stride length, arc of foot flight, and whether lameness is consistent or intermittent. Record a lameness score using a 0 to 3 or 0 to 4 scale, depending on the system used in your region, and note which limb or limbs are affected.

Restrain the sheep in a sitting position or on a tilt table. Examine all four feet, also the lame limb, because footrot frequently affects multiple feet and early lesions may be present without visible lameness. Clean the feet with a brush and water, then inspect the interdigital space, the coronary band, the sole, and the heel. A footrot scoring system such as the one developed in Australian research settings grades lesions from 0 (no lesion) through to advanced stages with underrunning of the sole and horn separation. Record the worst lesion on each foot separately.

Palpate the coronary band for swelling, heat, or pain. Apply gentle pressure to the sole and heel to detect abscessation. Use a hoof knife cautiously to explore suspicious areas, but avoid excessive trimming that removes healthy horn and delays healing. The distinction between superficial interdigital dermatitis and full footrot rests on the presence of underrunning: footrot characteriztically causes separation of the horn from the underlying sensitive tissue, whereas interdigital dermatitis remains confined to the skin surface.

Decision Points That Change the Diagnostic Path

Several findings redirect the investigation. If the coronary band is swollen and painful with no interdigital lesion, suspect contagious ovine digital dermatitis (CODD) or a pedal joint infection. If a single foot is affected with a discrete sole abscess and no interdigital involvement, white line disease or a foreign body is more likely than footrot. If multiple feet are affected with symmetrical interdigital erythema and no underrunning, ovine interdigital dermatitis is the probable diagnosis.

The flock context matters. In a flock with no previous footrot history and a single lame animal, sporadic causes such as trauma or abscess are more probable. In a flock with endemic lameness and multiple affected animals, infectious causes dominate. Infectious causes of lameness in sheep can pose problems for diagnosis and treatment at both the individual and flock level, and the clinician should adjust the index of suspicion accordingly.

Laboratory Sampling Strategy

Sample Collection Technique

Collect swabs from the interdigital space before any foot trimming that could contaminate the sample. Use a sterile cotton or rayon swab, rotate it firmly along the interdigital skin and the junction between healthy and diseased horn, and place it in transport medium appropriate for the laboratory method planned. For PCR, a dry sterile swab in a sterile tube is usually sufficient. For culture, use Amies medium with charcoal.

Pooling strategies reduce cost without sacrificing diagnostic accuracy. A pool of five swabs from different feet or different animals can be tested by PCR with detection equivalent to testing individual samples. This approach is particularly useful for flock screening, where the question is whether D. nodosus is present in the group instead of which individual animal is infected. Pooled sampling with pools of five has been shown to be a suitable and cost-effective method for detecting footrot at the flock level.

Test Selection and Interpretation

PCR is the reference method for D. nodosus detection. It does not distinguish between benign and virulent strains unless a specific virulence-associated gene assay is used, so request a PCR that includes virulence testing when the clinical picture is ambiguous. Culture remains useful for strain typing and antimicrobial susceptibility testing, but its lower sensitivity means a negative result should be interpreted cautiously.

Do not rely on laboratory testing alone. The clinical picture, lesion distribution, and flock history remain the primary diagnostic tools. Laboratory confirmation supports the diagnosis, guides strain typing, and provides a baseline for monitoring control programs. Clinical examination can identify infected animals, but PCR must be used to confirm the diagnosis.

Differential Prioritization by Clinical Presentation

The following table prioritizes differentials based on the dominant clinical finding. Use it as a guide, not a substitute for individual case assessment.

Brucellosis can cause lameness as part of a systemic presentation, and should be considered when lameness occurs alongside abortion, infertility, or weight loss in a flock, particularly in regions where the disease is not yet eradicated. The zoonotic potential of Brucella species means that any suspicion warrants immediate laboratory investigation and appropriate biosecurity precautions.

Monitoring Parameters and Documentation

Document every examination systematically. Record the lameness score, the lesion score for each foot, the distribution of affected feet, and the presence or absence of underrunning. Photographs are valuable for tracking progression and for communication with laboratory personnel or other advisors.

For flock-level monitoring, calculate the prevalence of lameness and the proportion of feet affected. Track these metrics over time to assess whether the diagnostic picture is stable, improving, or deteriorating. Changes in the pattern of lesions, such as a shift from interdigital dermatitis to full footrot, indicate that control measures are failing or that a different pathogen has become involved.

The environment influences disease expression. Moist and warm conditions, inadequate hygiene, and insufficient foot care are critical risk factors for foot-related lameness. Record housing conditions, bedding quality, and pasture drainage at each visit, because these factors determine whether the diagnosis is likely to recur and whether the current presentation reflects a new infection or persistent environmental pressure.

Production System and Regional Considerations

The diagnostic approach must adapt to the production system. In dairy sheep kept in semi-intensive or intensive systems, foot-related lameness may be more severe and more prevalent than in extensive meat or wool flocks. Footrot, contagious ovine digital dermatitis, ovine interdigital dermatitis, white line disease, and pedal joint abscess are the most common causes of foot-related lameness in dairy sheep, and the clinician should expect a higher baseline prevalence in these systems.

In extensive systems, lameness may be noticed later, lesions may be more advanced at presentation, and individual animal handling is more difficult. Sampling strategies that rely on pooling and flock-level testing are particularly valuable in these settings. In regions where footrot is notifiable or subject to control programs, laboratory confirmation is mandatory and the diagnostic pathway must include the relevant reporting requirements. International standards for animal health surveillance and trade-related disease control may apply, and the clinician should be aware of the obligations in their jurisdiction.

The availability of diagnostic services varies. In some regions, PCR for D. nodosus is routine and inexpensive, in others, culture is the only option and results take longer. When rapid results are unavailable, the clinical diagnosis must stand on its own, and treatment decisions should be made on the basis of the lesion pattern and flock history instead of waiting for laboratory confirmation.

Recognized Complications and Early Detection

The principal failure mode in footrot diagnosis is misclassification of the causative agent, particularly confusion between footrot and contagious ovine digital dermatitis (CODD). Footrot begins at the interdigital skin and progresses under the horn of the heel and sole, whereas CODD typically initiates at the coronary band and extends distally. Early detection depends on systematic scoring at each examination. A sheep that is lame but shows no interdigital lesion should not be dismissed, the clinician must examine the coronary band, the dorsal wall, and the sole separately. Clinical footrot scores and lameness scores correlate strongly with PCR detection of Dichelobacter nodosus, so a structured score recorded at first examination provides the baseline against which progression or response is measured.

A second failure mode is the assumption that a single lame sheep represents an isolated problem. Footrot is a flock disease, and the diagnostic unit is the group, not the individual. When one animal is affected, the clinician should examine a representative sample of the flock, including apparently sound sheep, because subclinical carriers maintain transmission. Infectious causes of lameness in sheep, including footrot, are best understood as flock-level problems that require integrated diagnostic and control planning.

A third failure mode is delayed recognition of secondary bacterial invasion. Fusobacterium necrophorum and Trueperella pyogenes can convert a superficial footrot lesion into a deep pedal joint infection. The discriminating finding is the site of maximal pain: footrot responds to pressure on the interdigital space and heel, while a pedal joint abscess produces pain on manipulation of the affected digit and often a visible swelling at the coronary band. Early detection requires palpation of each digit independently and comparison of the two claws.

Common Diagnostic Errors and Corrective Action

The most frequent error in teaching settings is failure to lift and restrain the foot properly. A sheep examined in sternal recumbency with the foot held by an assistant allows only a cursory view. The correct approach is to place the sheep in a sitting position with the hindlimbs extended or to use a tilt table for forelimb examination. Each claw must be separated and the interdigital space inspected with adequate light. Without this, early lesions are missed and the diagnosis defaults to footrot on the basis of lameness alone.

A second error is over-reliance on clinical appearance without laboratory confirmation. Clinical examination can identify animals infected with D. nodosus, but PCR is required to confirm the diagnosis. The corrective action is to sample the interdigital space of several affected and several unaffected animals when the diagnosis is uncertain or when the flock has not responded to previous treatment. Pooled sampling of five animals is a cost-effective strategy that does not reduce detection sensitivity.

A third error is failure to consider non-infectious causes when the foot is grossly normal. White line disease, foreign body penetration, and laminitis can all produce lameness without interdigital inflammation. The clinician who stops at the foot without examining the limb, the joints, and the spine will miss polyarthritis, which is common in lambs and may present with lameness in multiple limbs. Foot-related lameness in dairy sheep is caused by a defined set of conditions, and the diagnostic approach must distinguish these from each other and from systemic disease.

Limitations of Current Evidence and Areas of Expert Disagreement

The evidence base for ovine lameness diagnosis is uneven. Footrot is well characterized, with validated scoring systems and PCR diagnostics. CODD is less well understood, particularly its transmission dynamics and the relative contribution of Treponema species. Research on CODD has improved farmer and veterinarian knowledge, particularly in biosecurity and antibiotic use, but therapeutic and vaccine development remain priorities. Expert opinion differs on whether CODD can occur without prior footrot infection or whether footrot lesions predispose the coronary band to Treponema invasion. The clinician should therefore record the presence or absence of footrot lesions in every CODD suspect and report both findings.

There is also disagreement on the role of foot trimming in diagnosis. Some authorities advocate minimal trimming to preserve horn and avoid trauma, while others recommend aggressive exploration of the sole to identify deep lesions. The safe position is to trim only enough to visualize the lesion, record the extent of under-run horn, and avoid cutting into healthy tissue. This preserves diagnostic information and reduces iatrogenic damage.

Referral, Specialist Consultation, and Regulatory Reporting

Most footrot diagnoses are made in the field without specialist input. Referral is warranted when the diagnosis remains uncertain after clinical examination and PCR, when a suspected CODD outbreak is not responding to treatment, or when the clinician suspects a notifiable disease. Brucellosis can cause lameness in sheep and is a reportable disease in many jurisdictions, the clinician should consider it when lameness is accompanied by abortion, orchitis, or epididymitis. Brucellosis is a serious zoonotic disease that requires detection and slaughter of infected animals for eradication, and suspicion should trigger immediate regulatory consultation.

Laboratory involvement is indicated for PCR confirmation of D. nodosus, for culture when antimicrobial susceptibility is needed, and for histopathology when neoplasia or chronic granulomatous disease is suspected. The clinician should contact the laboratory before sampling to confirm the required transport medium and the expected turnaround time.

Regulatory reporting obligations vary by jurisdiction. The clinician should know the list of notifiable diseases in the local area and should consult WOAH terrestrial animal health standards and USDA APHIS livestock and poultry disease information for current reporting requirements. When in doubt, a telephone call to the relevant authority is preferable to failing to report. The MSD Veterinary Manual provides a general reference for disease recognition, but it does not supersede local regulatory requirements.

Frequently Asked Questions

How Should I Prioritize Diagnostic Testing When Farm Resources Are Limited?

Start with a structured clinical examination of all lame sheep, as clinical footrot scores correlate strongly with PCR detection of Dichelobacter nodosus (clinical footrot scores correlate with PCR detection). When PCR is unavailable or cost-prohibitive, careful lesion scoring and lameness grading provide a reliable working diagnosis for most flocks. Reserve PCR for confirming footrot in flocks where the diagnosis is uncertain, where CODD is suspected, or where eradication programs require verification. If you can collect only one sample type, take interdigital swabs from several affected animals and pool them, as pools of five samples detect D. nodosus as effectively as individual samples (pooled swabs are cost-effective for footrot detection). Bacterial culture offers high specificity but lower sensitivity than PCR, so negative cultures do not exclude footrot.

What Do I Do When I Cannot Distinguish Footrot from CODD on Clinical Examination Alone?

Separate affected animals and treat them as potentially carrying both pathogens until laboratory results return. CODD typically presents with severe lameness and lesions originating at the coronary band, whereas footrot begins interdigitally and spreads under the sole (contagious ovine digital dermatitis causes severe lameness). Collect deep swabs from the advancing edge of the lesion for PCR targeting both D. nodosus and Treponema spp. While awaiting results, advise the farmer to isolate affected sheep, use separate footbathing equipment, and avoid trimming feet from multiple animals with the same instruments. Recent research uptake among UK veterinarians has improved CODD management through better biosecurity and antibiotic stewardship, so apply those principles even before confirmation (research has improved CODD management practices).

How Does the Diagnostic Approach Differ in Dairy Sheep Compared with Meat and Wool Breeds?

Dairy sheep under semi-intensive and intensive management face a higher burden of foot-related lameness, and the range of differentials is broader (foot-related lameness is more severe in intensive dairy systems). In dairy ewes, examine for white line disease and pedal joint abscess more frequently, as high milk yield, increased parity, and prolonged standing on wet concrete predispose to non-infectious claw lesions. Footrot remains the leading infectious cause, but the relative frequency of CODD and interdigital dermatitis may differ from extensive wool flocks. Housing conditions, hygiene status, and foot care practices are the most critical risk factors, so adjust your diagnostic workup to include a thorough assessment of the housing environment and milking parlour standings (environmental factors determine foot lameness occurrence).

What Records Should I Maintain During a Lameness Investigation?

Record each examined sheep's identification, lameness score, lesion location and severity, and the specific differentials considered at first examination. Document which feet were affected, whether lesions were interdigital, solar, or coronary, and photograph representative lesions where possible. Note the laboratory tests requested, sample types, and results, then link those results back to the clinical findings. This documentation supports longitudinal monitoring and allows you to detect changes in lesion patterns over time. For regulatory purposes, maintain clear records of any reportable disease suspicions and the actions taken (USDA APHIS provides disease reporting guidance). Good records also enable you to evaluate whether the diagnostic approach is identifying the correct problem or whether repeated lameness indicates a missed differential.

How Should I Explain the Diagnostic Uncertainty to a Farmer Who Wants a Definitive Answer Immediately?

Explain that clinical examination identifies the most likely cause but that several foot diseases share overlapping features. Use the analogy that footrot and CODD can look similar in early stages, and laboratory testing distinguishes them reliably. Emphasize that the diagnostic plan is designed to avoid treating the wrong condition, which wastes time and money and prolongs suffering. Describe what each test will add and how long results will take. Note that footrot confirmation by PCR is highly reliable and that clinical scores correlate well with test results, so the working diagnosis is usually correct (PCR confirms the clinical diagnosis of footrot). Reassure the farmer that the examination findings already guide immediate biosecurity measures while laboratory confirmation refines the long-term plan.

When Should I Suspect a Systemic or Non-Foot Cause Despite a Prominent Foot Lesion?

If a sheep has a typical footrot lesion but fails to respond to appropriate foot care and topical therapy, or if multiple sheep develop lameness simultaneously with fever, weight loss, or abortion, broaden the differential. Infectious causes of lameness include systemic diseases that present with joint or limb involvement instead of primary foot pathology (infectious causes of lameness include systemic disease). Brucellosis can cause lameness alongside reproductive signs, and diagnostic serology should be considered in flocks with abortion storms or unexplained lameness (brucellosis causes lameness and requires serological diagnosis). Examine the limb above the foot for joint swelling, tendon sheath distension, or fractures. If foot lesions are present but mild relative to the degree of lameness, investigate the proximal limb and spine before attributing the problem solely to footrot.

Related Clinical & Scientific Guides

• Rumen Health Assessment in Dairy Cows: Clinical and Subclinical Indicators
• Mastitis Control Programs in Dairy Herds: Monitoring and Prevention
• Swine Nutrition and Health: Feed-Related Disease Diagnosis

References and Further Reading

• [[Claw infections in sheep - treatment options in veterinary practice, with special emphasis on ovine footrot treatment. - An update].](https://pubmed.ncbi.nlm.nih.gov/30616280/). 2018.
• [[Infectious causes of lameness in sheep - treatment options in veterinary practice].](https://pubmed.ncbi.nlm.nih.gov/23242151/). 2012.
• Aetiology, Risk Factors, Diagnosis and Control of Foot-Related Lameness in Dairy Sheep.. 2019.
• Brucellosis: Improved Diagnostics and Vaccine Insights from Synthetic Glycans.. 2017.
• Impact of research on contagious ovine digital dermatitis on the knowledge and practices of UK sheep farmers and veterinarians.. 2022.
• Prevalence of Dichelobacter nodosus in western Austrian sheep flocks: Comparison of bacterial cultures, clinical foot rot and lameness with PCR and analysis of sample pooling for PCR diagnosis.. 2024.
• USDA APHIS Animal Health Information. USDA APHIS.
• FAO Animal Production and Health. FAO.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.

Related Articles

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• Diagnostic Approach to Lameness in Dairy Cattle: Lesion Localization
• Diagnostic Approach to Downer Cow Syndrome: Metabolic vs. Traumatic Causes

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.