Abstract
Ovine footrot is a degenerative disease of sheep feet leading to the separation of hoof-horn from the underlying skin and lameness. This study quantitatively examined histological features of the ovine interdigital skin as well as their relationship with pro-inflammatory cytokine (IL-1β) and virulent Dichelobacter nodosus in footrot. From 55 healthy and 30 footrot ovine feet, parallel biopsies (one fixed for histology) were collected post-slaughter and analysed for lesions and histopathological analysis using haematoxylin and eosin and Periodic Acid-Schiff. Histological lesions were similar in both conditions while inflammatory scores mirror IL-1β expression levels. Increased inflammatory score corresponded with high virulent D. nodosus load and was significant (p < 0.0001) in footrot feet with an inflammatory score of 3 compared to scores 1 and 2. In addition, in contrast to healthy tissues, localisation of eubacterial load extended beyond follicular depths in footrot samples. The novel inflammatory cell infiltration scoring system in this study may be used to grade inflammatory response in the ovine feet and demonstrated an association between severity of inflammatory response and increased virulent D. nodosus load.
Highlights
Lameness in sheep, caused by interdigital dermatitis (ID) and footrot, is widespread in the UK, having a major welfare and economic impact
Footrot is defined by separation of the hoof from the underlying structures and an accumulation of necrotic material, with varying degrees of severity (Beveridge, 1941; Thomas, 1962), this damage is believed to be mediated by immune pathology rather than by bacterial enzymes and toxins (Egerton, Roberts & Parsonso, 1969)
No differences between healthy and footrot samples were seen with regards to the area of ballooned cells (Fig. 5B; n = 55 and 30 respectively)
Summary
Lameness in sheep, caused by interdigital dermatitis (ID) and footrot, is widespread in the UK, having a major welfare and economic impact. Footrot development is characterised by invasion of neutrophils and lymphocytes into the dermis and epidermis in response to bacterial invasion of the epidermis (Davenport et al, 2014; Egerton, Roberts & Parsonso, 1969). A recent histological study of clinically healthy and affected feet showed a progressive increase in lymphocyte and neutrophil infiltration into the dermis and epidermis between healthy, ID and footrot samples (Davenport et al, 2014). Cytoplasmic ballooning and nuclear condensation were observed in the stratum spinosum of the epithelium (Thomas, 1962), as well as areas of fibrosis indicating a chronic reaction to tissue damage (Egerton, Roberts & Parsonso, 1969)
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