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Evaluating topical treatments for digital dermatitis: Add a dose of skepticism

Laura Solano and Karin Orsel for Progressive Dairyman Published on 18 July 2017

Digital dermatitis (DD), known as hairy heel warts, strawberry foot rot, raspberry heel, Mortellaro’s disease and foot warts, has become the most common foot lesion on many dairy herds throughout North America. It seems there are as many prevention and treatment products for DD as there are names for the disease.

We are constantly presented with new products that come in a variety of shapes, sizes and formulations claiming to cure DD.

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Many of these “miracle products” hit the market before being properly tested in the lab or the field, lacking scientific evidence or regulatory approval. Hence, we need to seriously question the safety, cost-effectiveness, health and welfare consequences, and veracity of the claims for these new products.

Before using any of them, you should request research results that support the product’s efficacy instead of relying on simple testimony. If there is research to back up product claims, how do we assess whether the evidence is strong enough? Let’s find out.

Although questions still remain about the exact cause and progression of DD, bacteria of the Treponema genus are thought to be the primary bacteria involved, with a complex cycle of development and recurrence of lesions. Clearly, the best way to beat DD is to focus on prevention.

Unfortunately, DD prevention is not as easy as removing a single risk factor but, rather, a multi-pronged, long-term strategy is required. This prevention strategy includes biosecurity, hygiene, footbathing, early detection and immediate treatment of DD lesions.

Although it is not feasible to eliminate DD completely from the herd, we can mitigate risk factors and achieve what Dr. Dörte Döpfer describes as a “manageable state of disease,” with the occasional active, red, ulcer-like lesion (M2 stage, see Figure 1).

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Active, red ulcer-like lesion (M2 stage)

The best chance for a successful treatment is at this active M2 stage. We can spot lesions at this stage in the milking parlor or with pen walk inspections, done routinely every week to detect early and allow for immediate treatment. If left untreated, M2 lesions can develop into a chronic, more complicated stage that, without a proper footbath design and protocol, can recur.

Given that DD is a bacterial infection, the best way to treat it (supported by the most evidence) is with antibiotics. Although there are no antibiotics approved specifically for DD treatment, extra-label topical treatment with tetracycline or lincomycin is commonly used. However, there is a discrepancy between susceptibility of treponemes in the laboratory (in vitro) and in the field (in vivo).

In addition, there are other antibiotics that kill treponemes more effectively (for example, penicillin and erythromycin), but these are not widely used due to high costs and the necessity to withhold milk. Due to concerns over prudent antibiotic use and milk residues, stricter regulations for the use of tetracycline were recently implemented.

Hoof trimmers are no longer able to purchase tetracycline directly, and farmers will need a prescription from the herd veterinarian to continue using tetracycline. In wake of antibiotic restrictions and public health concerns, it is not surprising a number of non-antibiotic alternatives are being promoted.

For the sake of simplicity, this article will focus on DD topical treatment, but much of what is discussed here is also applicable to footbathing and other prevention strategies.

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Before trying a new product, look at the label directions for use, decide if you are able and willing to follow them (for example, if treatment needs to be done daily, or if hooves need to be cleaned before applying the product), but most importantly, request evidence for the product’s efficacy by asking a few basic questions:

  • Has the product been screened in the laboratory and tested in the field by an independent entity/body such as a university?

An initial screen of the product in the laboratory proves if it can kill or inhibit the bacteria associated with DD (treponemes). A product that doesn’t work in the lab will be useless in treating or preventing DD on the farm, as the farm’s environment is a lot more complex than sterile, “perfect” lab conditions.

Having said that, a product that works in the lab does not guarantee it will be effective on the farm. That is why the product should also be tested in the field, to provide evidence of its effectiveness under real-farm conditions.

If the product has been tested in a field trial, we can get a general idea of the reliability of the trial’s results by questioning:

  • Was there a group of cows that received the treatment and a separate group of cows that did not receive the treatment (treatment group versus negative control group)?

Comparing results of treated versus not treated cows increases reliability of the product’s effectiveness and helps rule out “alternative facts” about the product’s results.

For example, if at the end of the trial, treated and non-treated cows had the same cure rates, this can be attributed to spontaneous DD lesion healing due to seasonality or cows’ immune response rather than to the actual effect of the product being tested.

  • On how many cows (sample size) was the product tested, and were these cows selected randomly?

Generally speaking, as sample size increases, the margin of error and variation decreases. In other words, the more information you have, the more accurate the results. Also, a study that randomly assigns cows to treatment ensures cows had an equal chance of being placed in any group and were not intentionally selected to obtain better results.

  • For how long were cows followed up on after treatment and how was “DD cure” defined?

DD lesions cycle through different stages and severities over time. Research from the Iowa State University team demonstrated it may take three to four months for DD lesions to recur following treatment.

Although field trials of such prolonged duration are more expensive, they are required to confirm lesions fully heal and do not recur. Shorter observation periods may allow for observation of improvement rather than healing.

In conclusion, if considering new DD therapies, ask for evidence of effectiveness, critique the evidence and, very importantly, track your own progress by recording DD lesions. Record the proportion of cows per DD stage before and after using a new product and continue monitoring to evaluate the product’s performance.  end mark

Karin Orsel is on the faculty of Veterinary Medicine, University of Calgary. Email Karin Orsel.

Laura Solano
  • Laura Solano

  • Farm Animal Care Associates
  • Email Laura Solano

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