Footrot lesions recognition among 61 sheep farmers in Alentejo, Portugal

Identificação de lesões de peeira realizada por 61 produtores de ovinos no Alentejo, Portugal

ABSTRACT:

Lameness has been identified as a major welfare challenge in sheep farming production. The most common causes of lameness include several types of foot-related lesions. Accurate diagnosis of hoof lesions, particularly differentiating footrot from other foot disorders, is critical for implementing effective control strategies. This study assessed the ability of sheep farmers in Alentejo, Portugal, to recognise footrot lesions among other hoof disorders. A pictorial questionnaire depicting several hoof lesions, including footrot, interdigital dermatitis, contagious ovine digital dermatitis (CODD), toe granuloma, foot abscess, and shelly hoof, was applied to 61 Alentejo sheep farmers. Respondents identified which images represented footrot lesions and which of them they had previously observed in their flocks. Among the footrot images, the individual correct identification rate ranged from 95.1% to 100%. For other hoof disorders, the identification rate ranged between 88.5% (CODD) and 96.7% (shelly hoof). Eighty percent of the farmers (49/61) correctly answered all the eight questions. Farmers who reported no footrot in their flocks had a slightly higher accuracy (82.1%) compared to those who did (77.3%), though the difference was not statistically significant. In general, Alentejo sheep farmers evidenced a high level of accuracy in diagnosing footrot lesions, suggesting CODD does not look like to be an important confounding factor in Alentejo, as it mainly occurs in Great Britain.

Key words:
sheep farming; lameness; hoof lesions

RESUMO:

A claudicação tem sido identificada como um dos maiores entraves ao bem-estar na produção de ovinos. As causas mais comuns incluem vários tipos de lesões podais. Um diagnóstico correto das lesões podais, especialmente na diferenciação entre peeira e as restantes, é fundamental para a implementação de estratégias de controlo eficazes. Este estudo teve como objetivo à avaliação da capacidade dos produtores de ovinos no Alentejo, Portugal, de diferenciar lesões de peeira de outras afeções podais. Para realizar a avaliação, procedeu-se à aplicação de um questionário, em 61 criadores de ovinos, contendo imagens de diversas lesões como: peeira, dermatite interdigital, dermatite digital contagiosa ovina (CODD), granuloma de digital, abcesso digital e doença da linha branca. Os inquiridos identificaram quais as imagens que representavam lesões de peeira e quais delas já tinham observado anteriormente nos seus rebanhos. Além disso, entre as imagens de peeira, a percentagem de identificação correta variou de 95,1% a 100%. Já para as restantes lesões podais, a percentagem de identificação correta variou entre 88,5% (CODD) e 96,7% (doença da linha branca). Oitenta por cento dos produtores (49/61) responderam corretamente à totalidade das oito perguntas. Por outro lado, os produtores que reportaram não ter peeira nos seus rebanhos evidenciaram uma precisão ligeiramente maior (82,1%) em comparação com aqueles que afirmaram ter a doença (77,3%), embora a diferença não tenha sido estatisticamente significativa. Em geral, os produtores de ovinos do Alentejo demonstraram uma elevada precisão no diagnóstico de peeira, sugerindo que a CODD não parece ser um fator de confusão relevante no Alentejo, tal como ocorre na Grã-Bretanha.

Palavras-chave:
produção de ovinos; claudicação; lesões podais

INTRODUCTION

Lameness currently represents one of the most significant health and welfare challenges for sheep flocks worldwide (BEST et al., 2020). The term lameness refers to any deviation from the normal gait, caused by various lesions, injuries, or defects affecting different parts of the limbs. Most cases of lameness in sheep are attributed to foot-related disorders (GELASAKIS et al., 2019). A wide range of lesions may affect the hooves, each requiring distinct diagnostic, treatment and control approaches. Therefore, it is crucial for sheep farmers to acquire the competence and sensitivity necessary to differentiate foot lesions (KALER & GREEN, 2008). Although British farmers have demonstrated a relatively good ability to correctly identify the presence of foot lesions, incorrect diagnoses frequently occur. Misdiagnoses often involve hoof lesions wrongly attributed to footrot, such as contagious ovine digital dermatitis (CODD), white line disease (shelly hoof), foot abscess, and toe granuloma (KALER & GREEN, 2008; CONINGTON et al., 2010).

Footrot is a highly contagious disease and is considered the leading cause of lameness in sheep (RAADSMA & EGERTON, 2013; CAETANO et al., 2018; ZANOLARI et al., 2021). The disease is mainly caused by Dichelobacter nodosus (BEVERIDGE, 1941); although other bacteria, such as Fusobacterium necrophorum, also contribute to its pathogenesis (ALLWORTH, 2014; USIÉ et al., 2023). Initially, the infection is confined to the interdigital space and is characterised by inflammation of the interdigital epidermis (WINTER, 2008). Under favourable environmental conditions, the disease may progress to the separation of the hoof horn from the underlying sensitive tissues, a process known as underrunning (BENNETT & HICKFORD, 2011).

CODD, another infectious disease affecting sheep’s feet, is caused by spirochetes belonging to the genus Treponema (ANGELL et al., 2015). In its early stages, CODD presents as lesions of the coronary band, which differ markedly from those observed in footrot. However, in the more advanced cases, complete hoof separation may occur, resembling severe footrot lesions (SULLIVAN et al., 2015; GELASAKIS et al., 2019).

White line disease, also known as shelly hoof, is characterised by defects in the abaxial solar surface of the stratum corneum, which in severe cases result in detachment in the white line area (WINTER & ARSENOS, 2009; REEVES et al., 2019). Although, its pathogenesis remains unclear, environmental and genetic factors are considered to play major roles, while an infectious aetiology has been largely dismissed (WINTER & ARSENOS, 2009; GELASAKIS et al., 2019). Foot abscess, usually caused by Trueperella pyogenes (previously Arcanobacterium pyogenes) or F. necrophorum, represents another important cause of ovine lameness (WEST, 1983; WANI et al., 2015). This condition is characterised by purulent exudate, which may drain through the interdigital space and/or the coronary band (WINTER, 2008; GELASAKIS et al., 2019).

Toe granuloma, or digital granuloma, is characterised by hyperplastic growth of vascularised laminar corium following injury (GELASAKIS et al., 2019). This uncontrolled granulomatous tissue growth often results from excessive hoof trimming. Consequently, routine trimming sessions in uninfected sheep are no longer recommended (WINTER, 2008).

The present study reports the results of an investigation into the ability of Alentejo sheep farmers’ to identify footrot lesions. The study employed a questionnaire that included illustrative images of different sheep foot lesions, challenging respondents to identify which images represented footrot. Therefore, this research assessed and validated farmers’ diagnostic accuracy regarding footrot lesions, an essential step toward ensuring the reliability of epidemiological data collected in a subsequent survey conducted in the Alentejo region (unpublished results).

MATERIALS AND METHODS

Development of a pictorial questionnaire

The main objective of this study was to evaluate the ability of Alentejo sheep farmers to correctly recognise footrot lesions. Thus, a pictorial questionnaire was developed and applied to farmers, adapting the methodology proposed by KALER & GREEN (2008).

The questionnaire (Supplementary material 1) was designed as a single-page document written in Portuguese, attached by a file containing eight images and brief captions of different ovine hoof lesions (CODD, foot abscess, toe granuloma, shelly hoof, and four grades of footrot - scores 1-4, according to the scoring system of EGERTON & ROBERTS (1971) (Supplementary material 2). Participants were first asked to select the images they perceived as representative of footrot lesions. Subsequently, they were asked which of those lesions had been previously observed in their sheep flocks. Respondents were allowed to select any number of options, ranging from none to all.

Study population

The sample size was determined using Sample Size Calculator. Assuming an estimated disease prevalence of 50% in the region and aiming to collect 500 epidemiological questionnaires (unpublished results), a 10% margin of error and a 90% confidence interval (CI) of 90% were applied. These parameters yielded a required sample size of 61 farms to be investigated, ensuring a 90% probability that the true prevalence of each hoof disorder would lie within the range [μ-10%; μ+10%].

Application of the questionnaire

A pilot version of the questionnaire was initially tested on five farmers, after which minor adjustments were made based on their feedback. The final version of the questionnaire was then administered to sheep farm owners in the Alentejo region, selected through a randomised process. Data collection was carried out through face-to-face interviews to enhance reliability by enabling direct interaction with respondents (SHELLY & ROSENBLATT, 2011). Data was collected from September 1 till December 15, 2017.

Data analysis

The collected data was recorded and analysed using IBM ^® SPSS ^® Statistics software (version 26). Descriptive statistics were computed, and univariate analysis was performed using simple regression analysis. Proportion comparisons were conducted using the Chi-square test. Odds Ratios (OR) and their corresponding CI were calculated for selected parameters. A significance level of 0.05 was applied to all statistical tests.

RESULTS

Sample characterization

A total of 61 interviews were conducted, and all questionnaires were fully completed. Among the respondents, 22 farmers reported footrot in their flocks, representing 36% of the sample.

Hoof lesions recognition

Regarding the images presented to the participants, the proportion of correctly identified footrot lesions ranged from 95.1% (score 1) to 100% (score 4) (Table 1). In the case of the hoof lesions not directly attributed to D. nodosus, the proportion of correct answers ranged from 88.5% (CODD) to 96.7% (shelly hoof) (Table 2).

Overall, 80.3% of respondents answered all questions correctly (no mistakes). The probabilities of making one, two, or at least three mistakes were 9.8%, 3.3%, and 6.5% respectively (Table 3).

Table 1
Number of correct answers, respective to the four footrot scores images (N = 61).

Footrot Score	1	2	3	4
Number of correct answers	58	59	59	61
%	95.1	96.7	96.7	100

Table 2
Number of correct answers, respective to CODD, toe granuloma, foot abscess, and shelly hoof images (N = 61).

Foot injury	CODD	Toe granuloma	Foot abscess	White line disease
Correct answers	54	57	55	59
%	88.5	93.4	90.2	96.7

Table 3
Number of incorrect answers, from the eight questions, in the diagnosis of footrot (N = 61).

Number of mistakes	0	1	2	3	4	5	6	Total
Number of farmers	49	6	2	2	1	0	1	61
%	80.3	9.84	3.28	3.28	1.64	0	1.64	100

Analysis of farmers’ ability to recognise foot lesions, in relation to the reported presence/absence of footrot in their flocks, revealed that the proportion of farmers who answered all the questions correctly was higher among those who reported not having the disease (82.1%), compared with those who reported its presence (77.3%). Nevertheless, this difference was not statistically significant (χ² = 0.202; P = 0.65).

Among the farmers who reported footrot and did not answer all questions correctly (5 farmers; 22.7%), all made only one error (Table 4). Conversely, among farmers who did not report footrot, seven respondents (18.0%) failed to correctly diagnose footrot, with six (15.4%) making at least two mistakes (Table 4).

Table 4
Number of incorrect answers, based on the presence/absence of footrot.

Number of mistakes	0	1	≥ 2	Total
Farms with footrot	17	5	0	22
%	77.3	22.7	0	100
Farms with no footrot	32	1	6	39
%	82	2.6	15.4	100

Footrot lesions characterization

The analysis of footrot lesions was restricted to responses from farmers who reported the occurrence of footrot within their flocks (n = 22). Table 5 presents the proportion of flocks in which each footrot lesion score had been previously observed.

Table 5
Number of farmers who had previously observed different footrot scores (N = 22).

Footrot score	----------N----------	----------%----------
1	21	95.5
2	11	50
3	11	50
4	17	77.3

Before analysing the prevalence of other hoof disorders, four answers (6.6%) were excluded due to inconsistent response patterns. Thus, the number of valid questionnaires used to estimate the frequency of other hoof disorders based on farmers’ reports was 57. Table 6 shows the estimated prevalence, and corresponding CI, for CODD, shelly hoof, toe granuloma, foot abscess, and interdigital dermatitis. As the last one may involve a distinct pathogenesis from footrot, it was considered separately.

Table 6
Number of farms in which lesions of interdigital dermatitis, CODD, digital granuloma, foot abscess, and shelly hoof were observed (N = 57).

Hoof disorder	No. farms	%	CI 90%
Interdigital dermatitis	32	56.1	[46.1; 66.1]
CODD	6	10.5	[0.5; 20.5]
Toe granuloma	14	24.6	[14.6; 34.6]
Foot abscess	29	50.9	[40.9; 60.9]
Shelly hoof	19	33.3	[23.3; 43.3]

Correlation between footrot and other hoof lesions

A univariate analysis was performed to evaluate the association between the presence of footrot and reports of other hoof lesions. This analysis revealed that only one variable (CODD) was positively and statistically significantly associated with footrot (Table 7). Therefore, flocks in which CODD lesions were reported had a 33.62 higher likelihood of reporting footrot compared with those where CODD had not been observed.

Table 7
Univariate analysis between footrot and other hoof lesions.

Variable (N)		No. farms with footrot	--------%--------	-------OR-------	----CI 95%----	--------P--------
CODD	No (51)	14	27.5
	Yes (6)	6	100	33.6	[1.78; 636]	< 0.05
Toe granuloma	No (43)	13	30.2
	Yes (14)	7	50	2.31	[0.67; 7.92]	0.18
Foot abscess	No (28)	7	25
	Yes (29)	13	44.8	2.44	[0.79; 7.51]	0.12
Shelly hoof	No (38)	14	36.8
	Yes (19)	6	31.6	0.79	[0.25; 2.55]	0.7

DISCUSSION

The primary goal of this research was to assess the ability of sheep farmers in the Alentejo region of Portugal to recognise foot lesions, with particular emphasis on footrot. This evaluation represents a crucial step toward validating the accuracy of an ongoing epidemiological survey on footrot in Alentejo (unpublished results). The assessment provides objective evidence supporting the validity of the survey’s conclusions. Although, this approach is not ideal, it is a feasible one, given the economic and temporal constraints that precluded on-farm diagnostic testing for all sampled flocks. Consequently, a pictorial questionnaire was chosen as the most practical and cost-effective tool to evaluate farmers’ ability, following a similar methodology previously applied by KALER AND GREEN (2008). When direct clinical examination of animal feet is not feasible, photographic and illustrative assessments can provide a valid diagnostic alternative (KALER & GREEN, 2008). Furthermore, the use of colour images enhances engagement and motivation among respondents (KAPLOWITZ & LUPI, 2004). The calculated sample size of 61 questionnaires was based on the predetermined confidence level and margin of error.

The overall proportion of sheep farmers who correctly identified all footrot lesion images was 80.3%, a notably high value. This contrasts sharply with the findings of KALER & GREEN (2008) in England, in which only 22.5% of farmers correctly identified all lesions, suggesting a considerably lower diagnostic accuracy. British farmers often tend to classify any foot disorder as footrot (KALER & GREEN, 2008), a tendency likely influenced by the coexistence of both footrot and CODD in British sheep flocks, two major causes of lameness that frequently lead to misdiagnoses (ANGELL et al., 2014; WINTER et al., 2015). CODD is largely restricted to the UK (GELASAKIS et al., 2019) and, to date, has not been reported in Alentejo, which may partially explain the higher diagnostic accuracy among this Portuguese region. Nevertheless, a recent first report of CODD in Spain (BENITO et al., 2024), a country bordering Alentejo, warrants caution and advises further investigation about this topic.

Footrot has been recognised for over two centuries (BEVERIDGE, 1941), whereas CODD was first identified just over two decades ago (DUNCAN et al., 2012). The relative novelty of CODD may explain the historical misclassification of some CODD cases as footrot. This overlap is understandable given that both diseases, at their more severe stages, can produce similar clinical presentations, both leading to hoof horn detachment (RAADSMA & EGERTON, 2013; GELASAKIS et al., 2019). In Alentejo, the apparent absence of CODD as a confounding factor likely contributes to the higher accuracy rate observed in this study.

Farmers who reported no footrot in their flocks exhibited a slightly higher rate of correct answers (82.1%) compared to those who reported the disease (77.3%), although this difference was not statistically significant (P > 0.05). Notably, all farmers who reported footrot but failed to answer all questions correctly (22.7%) made only one error, suggesting minor misclassification. Conversely, among farmers who did not report footrot, most of those who made errors (6/7) missed two or more questions, indicating more significant diagnostic inaccuracies. These findings suggested that farmers with firsthand experience of footrot are less prone to substantial diagnostic errors, although this trend needs confirmation with larger sample sizes.

Among farmers who reported footrot, the most observed footrot lesions corresponded to scores 1 (95.5%) and 4 (77.3%). The high identification rate for score 1 is expected, as these mild lesions, also seen in ovine interdigital dermatitis (scald), are nonspecific (ABBOTT & LEWIS, 2005). Such lesions may even occur in flocks without footrot due to the opportunistic presence of F. necrophorum in healthy sheep (ATIA et al., 2017). Conversely, the high reporting rate of score 4 lesions indicates the presence of severe clinical forms, characterised by hoof horn separation, necrosis, and potential irreversible locomotion issues (RAADSMA & EGERTON, 2013). Future research should investigate the herd clinical form of footrot (benign, intermediate, or virulent) based on lesion score distribution, as disease impact varies markedly with disease severity (STEWART et al., 1986; RAADSMA & EGERTON, 2013).

Lesions classified as scores 2 and 3 were recorded at the same rate (50%), notably lower than scores 1 and 4. Given the predictable progression of footrot lesions, it is unusual for limbs to exhibit score 4 lesions without preceding moderate lesions (scores 2 and 3). This pattern suggests that some farmers may not be consistently monitoring disease progression, potentially intervening only when lesions become nearly irreversible. Another possible explanation involves the use of topical antibiotics, a common therapeutic procedure (GREEN & GEORGE, 2008). These medications can stain affected tissues for prolonged periods, obscuring the visual assessment of lesion progression.

Other hoof disorders not directly related to D. nodosus were also reported. Foot abscess was the most frequently reported lesion (50.9%), followed by shelly hoof (33.3%). Both conditions are typically associated with mechanical trauma to the hoof, compromising white line integrity and predisposing to bacterial colonization and abscess formation (WINTER, 2009). Although, the pathogenesis of these disorders is not fully understood, environmental and nutritional factors appear to play major roles (GELASAKIS et al., 2019).

Toe granuloma was reported by 24.6% of farmers. Despite its lower frequency, this proportion remains concerning, as this disorder arises exclusively from excessive hoof trimming (WINTER, 2008). CODD was the least frequently reported lesion (10.5%). Although, CODD cases remain scarce outside the UK (GELASAKIS et al., 2019), the recent detection of CODD in Spain (BENITO et al., 2024) underscores the need to evaluate its potential presence in Alentejo sheep flocks. The significant positive correlation between CODD and footrot observed in this study suggested that CODD could represent a potential risk factor for footrot in the Portuguese region. Should this relationship be confirmed, it would parallel the epidemiological situation described in the UK (ANGELL et al., 2014), emphasising the need for continued surveillance and further research.

In conclusion, the ability of Alentejo sheep farmers to diagnose footrot was remarkably high compared with results from other geographical contexts. These results provide crucial validation for the epidemiological survey conducted in the same region (unpublished results). Regarding the identification of other hoof disorders, the frequency reported by Alentejo farmers aligns with global trends. Thus, it is critical to invest in training programs for farmers, enhancing their ability to distinguish between different foot disorders. Moreover, disseminating technical knowledge on effective therapeutic and prophylactic measures for each type of lesion will be fundamental to improving flock health and welfare.

ACKNOWLEDGMENTS

The authors would like to thank all the farmers who contributed to this research. The authors acknowledge the R&D unit MED - Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento <https://doi.org/10.54499/UID/05183/2025> and the Associate Laboratory CHANGE - Instituto para as Alterações Globais e Sustentabilidade <https://doi.org/10.54499/LA/P/0121/2020>.

Supplementary Material

Supplementary Material

Available

<https://drive.google.com/file/d/1RuuiJhHdFQNTkiwoq8Xto2PzJ2wuaUDH/view?usp=sharing>.

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• CR-2025-0413.1
• BIOETHICS AND BIOSECURITY COMMITTEE APPROVAL
  We authors of the article entitled “Footrot lesions recognition among 61 sheep farmers in Alentejo, Portugal” declared, for all due purposes, the project that gave rise to the present data of the same has not been submitted for evaluation to the Ethics Committee of the Universidade de Évora / MED - Instituto Mediterrâneo para a Agricultura, Ambiente e Desenvolvimento, and CHANGE - Instituto para as Alterações Globais e Sustentabilidade, but we are aware of the contents of Resolution No. 466, of December 12, 2012 of the Brazilian National Health Council <http://conselho.saude.gov.br/resolucoes/2012/Reso466.pdf> if it involves human. Thus, the authors assume full responsibility for the presented data and are available for possible questions, should they be required by the competent authorities.
• DATA AVAILABILITY STATEMENT
  The data that support the findings of this study are available from the corresponding author upon request.
• DECLARATION OF USE OF ARTIFICIAL INTELLIGENCE
  The authors did not use artificial intelligence to develop this work.
• Funding Statement
  There was no funding for this publication

Edited by

• ASSOCIATE EDITOR:
  Rudi Weiblen (0000-0002-1737-9817)

• SCIENTIFIC EDITOR:
  Juliana Felipetto Cargnelutti (0000-0002-3160-3643)

Data availability

The data that support the findings of this study are available from the corresponding author upon request.

Publication Dates

• Publication in this collection
  20 July 2026
• Date of issue
  2026

History

• Received
  06 Aug 2025
• Accepted
  15 Dec 2025
• Reviewed
  04 Mar 2026