The objectives of the present study were to investigate the effect of parenteral treatment with gamithromycin in 3 footrot infected herds over time and to investigate the presence of DNA from D. nodosus and F. necrophorum on hoofs of footrot affected animals. Further objectives were to evaluate how the use of pooled samples to detect footrot on herd level at different herd prevalences influences the test compared to individual samples and finally to compare clinical scores and real-time PCR for diagnosing footrot.
Results from this study indicate that whole herd treatment with gamithromycin efficiently removed D. nodosus and associated clinical signs. All PCR tests were negative on day seven and 28 after treatment and all animals being scored healthy at day 28 by the clinical evaluation.
The prevalence of F. necrophorum was found to range between 6 and 33%. Association between D. nodosus and F. necrophorum and clinical score and F. necrophorum, respectively, was found in the herd with the highest prevalence of F. necrophorum. F. necroporum has been suspected to play a role in the pathogenesis of ovine footrot.
Analysis of pools from four and four animals, gave the same information as individual samples. This indicates that pooled samples are a precise, efficient and cost-effective method when the goal is diagnostics on herd level. However, examples in this study shows the herd level prevalence of footrot should be considered. The current approach among Danish sheep veterinarians is to sample only eight animals of a herd and to analyse these as two pools. This will only give a reliable result provided that the herd prevalence is greater than 32%. This indicates that pooled samples, as they are used today, are not sufficient when the goal is to declare a herd free from footrot if the prevalence is low.