Comparison of footbathing and vaccination to control ovine footrot in an experimentally infected flock

Abstract

Objective Compare footbathing and vaccination for control of footrot during a transmission period in a sheep flock deliberately infected with multiple strains of Dichelobacter nodosus. Methods The strains included a known virulent strain, a benign strain and several intermediate strains. The resulting footrot was clinically intermediate. A total of 1450 Polwarth sheep aged 1–3 years were allocated to one of five treatment groups: untreated, weekly walkthrough zinc sulfate footbathing, 1‐hour stand‐in Footrite® footbathing every 3 weeks, vaccination with a commercial multivalent whole‐cell vaccine and vaccination with a novel recombinant DNA fimbrial vaccine. There were four replicates, in four paddocks. Results Of the untreated animals, 76% had footrot. Footbathing, either weekly or every 3 weeks, restricted the prevalence to 6/283 (2%; 97% effective) and 18/275 (6.5%; 91% effective), respectively. This was significantly lower than the prevalence in either the untreated or vaccinated group (P < 0.001). Weekly footbathing resulted in significantly fewer affected sheep than footbathing for 1 h every 3 weeks (P < 0.05). Vaccination with either whole‐cell or recombinant vaccines significantly (P < 0.001) reduced the prevalence ((142/280 (51%; 33% effective), 114/278 (41%; 46% effective) respectively), with the recombinant vaccine superior (P < 0.05) to whole‐cell vaccination. Significantly (P < 0.05) fewer 1‐year‐old sheep had footrot than older sheep. A single Footrite treatment reduced the prevalence to 12% (53/445) compared with a prevalence of 57% (27/47) for untreated sheep (79% effective). Conclusion In this study footbathing was more effective than vaccination at controlling and treating multistrain footrot.

Relationship between the likelihood of footrot elimination from a flock and the virulence of the strain of Dichelobacter nodosus present

“…Similarly, although less frequently isolated than serogroup E isolates, serogroup H isolates were easily detected both pre‐elimination and in mob 4 during the post‐elimination sampling, again suggesting with some certainty that strain H was eliminated from all three mobs. Although serogroup A isolates were less frequently isolated from mob 4 during the post‐elimination sampling compared with both E and H isolates, they were still isolated from a number of sheep and had been easily detected in all mobs pre‐elimination . Given its virulence, and the apparent appropriate conditions for footrot expression, it seems that the virulent strain A was also eliminated from the three mobs in which elimination was the objective.…”

“…The initial spring control groups were likely to have sheep with similar susceptibility. The high level of footrot control achieved in the footbathed groups in particular should have ensured the retention in the trial mobs of a large number of susceptible sheep, given the high footrot prevalence in the untreated control group . The favourable response to the single Footrite treatment prior to the commencement of elimination would also have restricted the number of footrot susceptible sheep being culled.…”

“…Specimens for bacteriology were collected by scraping across the IDS and streaking the material onto a 4% hoof agar plate . Isolates were subcultured and serogrouped by the slide agglutination method .…”

“…[7][8][9] A large on-farm study was set up to further investigate the elimination of different strains of D. nodosus. The successful establishment of a flock with multiple D. nodosus strains 10 and the application of different control methods to this flock during the spring transmission period 11 produced a flock that was likely to have both clinically affected and cured sheep in it. The success of an elimination program in this flock was evaluated and is described here.…”

In this issue – October 2018: Mechanisms and treatment of tumour angiogenesis is · Coagulation times depend on methods used · Experimental studies on footrot control · Pasteurella multocida in pigs and poultry · Pomegranate poisoning in cattle · Outcome of foals with hypernatremia

“…In addition to this main trial, a further trial was performed to assess the virulence of the strains used (Experiment 3 in paper 1) . Paper 2 has a flowchart that follows the route of these sheep through the studies …”