Characterisation of Dichelobacter nodosus on Misshapen and Damaged Ovine Feet: A Longitudinal Study of Four UK Sheep Flocks.

Caroline M Best,Rosemary Grogono-Thomas,Alison Z Pyatt,Kate Phillips,Janet Roden,Tristan Cogan,Malgorzata C Behnke

doi:10.3390/ani11051312

Abstract

Simple SummaryThe bacterium Dichelobacter nodosus is the cause of footrot in sheep: a painful, contagious foot disease. Some sheep may be more susceptible to carrying D. nodosus on their feet, despite showing no signs of disease, and pose a risk to flock health and welfare. This study investigated whether misshapen or damaged feet (poor hoof conformation) were more likely to have D. nodosus present and in greater quantities than feet in good condition. Eighty-five ewes from four flocks were examined three times, on average, across a 12-month period. Poor hoof conformation traits were observed in over 92% of foot observations. Feet with poor sole and heel conformation were more likely to have higher quantities of D. nodosus than those in good conformation. Furthermore, on feet positive for D. nodosus, wall overgrowth contributed towards higher D. nodosus load. We highlight feet with aspects of poor conformation traits to covertly harbour D. nodosus. These feet could transmit D. nodosus to other feet of sheep. Increasing our understanding of D. nodosus infection is crucial in helping farmers improve management practices to reduce footrot.Dichelobacter nodosus is the causal agent of ovine footrot, a contagious disease of welfare and economic concern worldwide. Damaged feet may be subclinical carriers of D. nodosus and covertly spread infection. Accordingly, we evaluated the risk of misshapen and damaged feet on D. nodosus presence and load in four commercial UK sheep flocks. Foot-level observations and swabs (n = 972) were collected from ewes (n = 85) over 12 months. On average, ewes were sampled three times. Feet were inspected for disease and scored (good/poor) for three hoof conformation traits (sole and heel, wall, and wall overgrowth). Swabs were analysed for presence and load of D. nodosus, and mixed models were constructed. Poor hoof conformation traits were present in 92.5% of foot-level observations. Feet with poor sole and heel conformation were more likely to have higher D. nodosus loads (β = 0.19, 95% CI: 0.04–0.35) than those with good conformation. Furthermore, on feet positive for D. nodosus, wall overgrowth was associated with higher D. nodosus loads (β = 0.27, 95% CI: 0.01–0.52). Feet with aspects of poor conformation covertly harbour D. nodosus and are a source of infection. Flock management should be guided by hoof conformation to reduce disease challenge.

Highlights

Ovine footrot is a contagious disease of significant concern to sheep producers worldwide [1]
Investigating the role hoof conformation plays in the infection dynamics of D. nodosus is vital to understanding the biological mechanisms affecting host susceptibility and mitigating the welfare and economic costs associated with footrot
Whilst hoof wall overgrowth can be the result of non-weight bearing from previous footrot infection, or due to the diseased hoof horn growing more rapidly [13], we consider D. nodosus to have the potential to recrudesce in overgrown feet—a source of re-infection

Summary

Introduction

Ovine footrot is a contagious disease of significant concern to sheep producers worldwide [1]. Damage to the interdigital skin is essential for invasion of D. nodosus into the hoof epidermis and for disease to initiate [3] Environmental factors such as rainfall [13], pasture quality [14], and soil type [12], have been implicated in mediating clinical development of footrot by increasing the probability of a foot becoming damaged [15]. Secondary pathogens, such as Fusobacterium necrophorum, opportunistically colonise footrot-affected feet and increase disease severity [11]

Objectives

Results

Discussion

Conclusion