A within farm clinical trial to compare two treatments (parenteral antibacterials and hoof trimming) for sheep lame with footrot

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Abstract

From observational studies, farmers who use parenteral antibacterials to promptly treat all sheep with footrot (FR) or interdigital dermatitis (ID) have a prevalence of lameness of <2% compared with a prevalence of 9% lameness reported by farmers who treat lame sheep by trimming affected feet. We tested the hypothesis that prompt treatment of sheep lame with naturally developing FR or ID with parenteral and topical antibacterials reduces the prevalence and incidence of lameness with these conditions compared with less frequent treatment with trimming of hoof horn and applying topical antibacterials. A further hypothesis was that reduction of ID and FR would improve productivity. A lowland sheep flock with 700 ewes was used to test these hypotheses in an 18-month within farm clinical trial with four groups of ewes: two intervention and two control. The duration and severity of lameness was used to categorise sheep into three weighted scores of lameness (WLS): never lame (WLS0), mildly lame/lame for <6 days (WLS1) and severely or chronically lame (WLS2). The intervention reduced the prevalence of lameness due to FR and ID in ewes and lambs and the incidence of lameness in ewes. The WLS was also significantly lower in sheep in the intervention groups. Ewes with a higher WLS were subsequently significantly more likely to have a body condition score <2.5 and to have lame lambs. Significantly more ewes lambed and successfully reared more lambs that were ready for slaughter at a younger age in the intervention versus control groups. There was an increase in the gross margin of £630/100 ewes mated in the intervention group, including the cost of treatment of £150/100 ewes mated. We conclude that prompt parenteral and topical antibacterial treatment of sheep lame with ID and FR reduced the prevalence and incidence of these infectious conditions and led to improved health, welfare and productivity.

Introduction

Lameness is one of the greatest concerns for poor welfare in sheep (Goddard et al., 2006, Fitzpatrick et al., 2006). It has been estimated to cost the UK industry £24 million/annum (Nieuwhof and Bishop, 2005). More than 90% of farmers in the UK report lameness in their sheep, with a farmer-estimated prevalence of 10% with more than 80% of lameness caused by footrot (FR) and interdigital dermatitis (ID) (Grogono-Thomas and Johnston, 1997, Kaler and Green, 2008). In a study of 209 sheep farmers, those treating all sheep with FR with parenteral antibacterials and foot sprays reported a significantly lower peak prevalence of FR of 2% compared with the 9% reported by farmers who treated FR by paring the hoof horn and spraying disinfectant on to the foot (Wassink et al., 2003). In addition, farmers who reported prompt treatment of mildly lame sheep also reported a lower prevalence of lameness than those treating groups of lame sheep (Kaler and Green, 2008). Further evidence for the benefits of parenteral antibiotics comes from a prospective longitudinal study of 160 sheep on one farm where the treatment of sheep with FR and ID with parenteral and topical antibacterials was associated with a lower incidence of lameness in the subsequent 4 weeks (Green et al., 2007).

Dichelobacter nodosus is the necessary pathogen to cause FR (Beveridge, 1941) and is present in the majority of cases of both ID (inflammation of the interdigital skin) and FR (separation of hoof horn from the underlying tissue) (Moore et al., 2005). As a consequence, ID and FR are often a continuum of the same disease. The terms that are equivalent to ID and FR in Australia are benign and virulent FR (Depiazzi et al., 1991). D. nodosus is an anaerobic bacterium that has no known resistance to antibacterials. Parenteral antibacterial treatment of FR leads to recovery from lesions in over 90% of sheep (Sterk, 1960, Egerton et al., 1968, Grogono-Thomas et al., 1994) and in a recent factorial design study, over 90% of sheep with FR treated with long acting oxytetracycline recovered from lesions and lameness within 10 days whilst <30% sheep treated with foot trimming recovered in this time period (Kaler et al., 2010). This, together with the evidence above and biological reasoning, led to the hypothesis that prompt treatment of lame sheep with ID or FR with parenteral and topical antibacterials would reduce the prevalence (because of a reduced duration of lameness) and incidence (because a reduced infectious period would decrease the probability of transmission of D. nodosus between sheep) of lameness caused by these diseases compared with the traditional treatment of trimming hoof horn and applying a topical bactericide. Consequently, the health, welfare and productivity of the flock should increase. To test these hypotheses, a within flock clinical trial comparing these two treatments was set up on a convenience-selected farm in Oxfordshire with a commercial lowland spring-lambing flock of approximately 700, mainly North Country mule ewes. The objective was to compare prompt treatment of FR and ID with parenteral and topical antibacterials with a farmer's typical management of FR and ID (Wassink et al., 2003, Wassink et al., 2005) which includes less frequent treatment of lame sheep with ID and FR by trimming hoof horn and applying a topical bactericide. The study lasted from March 2005 to December 2006.

Section snippets

Study design March to September 2005

A sample size calculation was used to estimate the number of ewes required per treatment to test a reduction in lameness of 50% assuming a prevalence of lameness of 10%, 80% power and 95% significance. A total of 147 ewes were required per treatment.

Ewes lambed from the second week of March 2005. Ewes and lambs were identified with both ear tags and flank markings. The age (dentition), body condition score (BCS) (MAFF, 1994) and conformation of feet of ewes were recorded. All foot lesions (//www.footrotinsheep.org/

Prevalence and incidence of lameness in ewes and lambs

Descriptive statistics are presented in Table 1, Table 2. The four groups started with similar numbers of ewes by BCS, foot conformation, FR and ID. Although there were fewer treatments in the control groups (Table 1, Table 2) there were significantly more episodes of lameness with a maximum locomotion score >2 compared with the intervention groups in both ewes and lambs (Table 3, Table 4) over the trial period. Ewes and lambs in the intervention groups were lame for significantly fewer days

Impact on prevalence and incidence of footrot and interdigital dermatitis

We have demonstrated that prompt treatment of individual lame sheep with parenteral and topical antibacterials given to those with FR or ID significantly reduced the prevalence and incidence of lameness in ewes compared with delayed treatment of individual lame ewes with FR/ID treated with foot trimming and topical antibacterials. This latter management is used by the majority of sheep farmers in the UK and elsewhere in the world and so was an ideal control to provide useful results to farmers

Conclusions

We conclude that prompt individual treatment of all lame sheep with ID and FR with parenteral and topical antibacterials reduced the prevalence of FR and ID in ewes and lambs and the incidence of these conditions in ewes. The reduced duration and severity of lameness improved the production of the flock through increased body condition in ewes which led to higher lambing rates, fewer deaths in ewes and lambs and earlier finishing of lambs. The cost–benefit was an increase in gross margin of

Acknowledgements

We thank the farm and shepherd for their compliance during this study. We thank Amanda Bosley, Carol Puttock, Trish Finlay, Anna Thomas, Phil Stokes and Tristen George for their assistance with data collection and to Ruth Allingham for laboratory work. This study was funded by the Department for Environment, Food and Rural Affairs (project number AW1021).

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