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

Abstract

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.

New Insight into the Prevalence and Risk Factors for Three Distinct Hoof Conformation Traits in UK Commercial Sheep Flocks

“…Furthermore, lameness was uncommon in our sample of ewes, where the majority of affected sheep were only showing mild signs of footrot, so ewes were weight-bearing on affected feet. Nonetheless, our findings corroborate those identifying the presence of wall overgrowth to be negatively associated with D. nodosus presence and load [ 18 ]. It is important to note that the farms recruited in this study had average flock lameness levels of ≤3%, and accordingly, had relatively low infection challenge.…”

“…Longer sward heights have been associated with increased risk of white line disease [ 23 ], footrot [ 19 ], and general lameness in sheep [ 34 ]. Although sole and heel damage could be indicative of a previous episode of SFR, as discussed previously [ 18 ], our finding that feet with signs of footrot are more likely to have higher sole and heel conformation scores aligns with work highlighting higher loads of D. nodosus on feet with sole and heel damage present [ 18 ].…”

“…At each visit, ewes were visually assessed for lameness [ 24 ] and body condition score (BCS) [ 25 ]. All four feet were first inspected for clinical disease, before all eight individual claws were assessed for three hoof conformation traits using four-point ordinal scoring systems ( Table 1 ), as described in [ 18 ]: (1) sole and heel conformation, (2) hoof wall conformation and (3) hoof wall overgrowth. Examples of conformation scores are presented in Figure 1 (sole and heel), Figure 2 (hoof wall) and Figure 3 (hoof wall overgrowth).…”

“…At each visit, ewes were visually assessed for lameness [24] and body condition score (BCS) [25]. All four feet were first inspected for clinical disease, before all eight individual claws were assessed for three hoof conformation traits using four-point ordinal scoring systems (Table 1), as described in [18]:…”

“…Damaged and misshapen hooves are also more at risk of clinical footrot and resultant lameness [ 17 ]. Feet with misshapen and damaged sole and heel areas have elevated levels of D. nodosus present, with these sheep acting as subclinical carriers of infection [ 18 ]. Moreover, overgrown hoof horn appears to increase loads of D. nodosus found on infected feet [ 18 ], which could explain why hooves with wall overgrowth have an increased risk of clinical footrot [ 19 ].…”