Threefold process required to break the cycle of infection
The key to preventing outbreaks occurring time after time is a threefold process. Firstly, the risk of lesions has to be reduced. Reducing exposure to slurry and keeping the feet as clean and dry as possible is essential. Scraping out passageways more frequently, avoiding pooling of slurry and the build-up of wet, poached bedding all help to lower risk.
Secondly, if new lesions do develop they must be treated quickly with topical antibiotics to stop them becoming chronically infected cattle that are likely to suffer repeat bouts of infection, which will severely affect their productivity. Where infection levels are high, regular assessment of all cattle is essential, and rapid treatment of those that are identified as affected with digital dermatitis. Making treatments an easy and safe process is important - use of a knap-sack sprayer can help to apply the topical antibiotics direct to the lesion. However, the ideal is still to lift the foot in the crush, where the lesion can be cleaned and dried before several applications of antibiotic are applied. Whatever antibiotic is used should be decided on with input from your local vet and consideration for the meat withdrawal of the product.
The final component of control is regular disinfection of the feet through footbathing. Whilst footbathing is common practice in dairy herds, it presents more of a challenge in beef herds. Therefore footbath design is crucial in making the process easy for both the farmer, and more importantly, the cattle. A footbath is most effective when incorporated into the normal routine and the more accustomed the cattle are to passing through it, the quicker the job. One idea is to footbath when cattle are removed from their pen for bedding or cleaning.
In terms of construction, a 'built in' concrete footbath rather than a plastic one can be more comfortable for the cattle as it will not move when they pass through it. Good flow is also important to minimise faecal contamination and displacement of the footbath contents. Although very popular, rigid plastic baths with pronounced ridges on the bottom are uncomfortable and are not recommended.
As well as considering flow when designing a footbath, it is important to pay attention to its position and how easy it is to fill, empty and clean out. The easier it is to maintain, the more likely it is to be used. The addition of a large-bore drain with an easy to remove bung can help with this.
Length, width and depth of the bath are also critical. Cattle should place each foot in the solution at least twice, but preferably three times. The animal must not be able to 'jump' the bath, so a length of at least 3m is required. Fixing high, solid side panels to the bath helps ensure cattle continue walking and sloping side panels at the bottom also ensure that they cannot walk on the sides of the bath. Sloping side panels also help reduce significant loss of the treatment solution through splashing, as does a higher entry step. To ensure feet are completely immersed in the footbath solution it must be filled to a depth of 10cm.
Despite the widespread practice of footbathing there are relatively few robust clinical studies on the effectiveness of the various agents that can be added to the bath. When deciding what to use the following should be considered: ease of use, product safety, disposal, cost and, most importantly, is it doing the job.
It is a common belief that footbathing agents act as 'treatments'. However, they are mainly acting as disinfectants. Pay attention also to the concentrations required. In some cases stronger isn't always better. For example, whilst formalin is a very effective disinfectant at concentrations of 1-2.5pc, it is possible that higher concentrations actually increase the likelihood of chronic lesions developing by driving digital dermatitis deep into the skin.
However, whichever agent is used, it is unlikely to work if it can't get to the target area. The full potential of the agent will not be achieved if the animal's feet are dirty or do not receive sufficient numbers of 'dunks' in the bath. Accurate measurements of the footbath must be taken to determine its volume when full so that sufficient agent is added to achieve the desired concentration. Whilst there is no robust data yet to support how often a footbath should be changed, as a general rule of thumb the footbath should contain one litre for every animal that passes through it. So a 200 litre footbath must be changed every 200 animals. However, this will depend on the level of contamination in the footbath and also on the agent being used. For example, copper sulphate is less susceptible to deactivation by faeces in comparison to formalin.
Sara Pedersen is a Welsh vet who hosted recent lameness workshops in Ireland with Devenish Nutrition
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