Digital dermatitis: Old disease, new research

By Terry J. Engelken, Iowa State University College of Veterinary Medicine

Reports of “hairy heel warts” or digital dermatitis have been described in cattle beginning in the early- to mid-1970’s. While first described in dairy cows, more recent reports have centered on the development of DD on beef cattle farms. 

A type of bacteria called Treponema has classically been blamed for the disease. This is based on consistent testing results that grew or identified the bacteria in the lesions.

Treponema is a group of bacteria and should not be considered as one organism. There are at least five different Treponema organisms that are consistently isolated from DD lesions, but many others have also been identified. 

However, it is becoming more evident that DD lesions should be considered more like a “complex” that involves multiple species of bacteria, the immune response at the skin level, and environmental conditions.

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Recent research done on dairy and feedlot cattle at the College of Veterinary Medicine at Iowa State has shown that the bacterial population changes as the lesions move from early stages to chronic at a dramatic pace. DD lesions were sampled and profiled for bacterial DNA in order to determine differences in the populations of bacteria as these lesions aged.

There were at least 11 different bacterial families represented in these lesions and the combination of bacteria changed dramatically as these lesions aged. While there was no indication of involvement of viruses or fungi, it is very clear that focusing on a single bacteria will not solve the puzzle of DD lesion development.

The development of DD lesions in feedyards has not been well defined. It is common for lameness to be exhibited close to the normal reimplant date, but that can be highly variable. Calves that have been through backgrounding programs may arrive at the feedyard with active lesions. Other factors such as co-mingling, breed or genetics, history of feeding dairy animals, or size of the cattle may also have an impact of the prevalence on DD. It is believed that any factor that negatively impacts the integrity of the skin on the animal’s heel can increase the likelihood of lesion development. Extremely wet pen conditions, excess manure buildup, exposed concrete edges, or rough surfaces can increase the likelihood of disease. Once established in the pen environment, it is difficult to eliminate the disease from the facility.

Treatment centers around bandaging the foot with an antibiotic (tetracycline or lincomycin) in individual animals or the use of foot baths to treat groups of cattle. Topical spray treatments using a hand sprayer may also be used but the effectiveness of this treatment is debatable. Cattle may need to have the lesions sprayed multiple days in a row making the time commitment costly. Treatment with an injectable antibiotic has been shown to have a low success rate in eliminating these lesions.

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Foot baths are the mainstay in treating pens of feedlot calves. A range of different products are effective including copper sulfate, zinc sulfate, formalin, and commercial chemicals containing quaternary ammonium compounds, organic acids, and other disinfectants. It is essential that the volume of the foot bath is known so that the correct amount of chemical may be used to provide the appropriate final concentration. 

The volume in gallons can be calculated from the formula of length × width × depth (in inches) divided by 231. Foot baths should be at least 8 feet long and 5 inches deep to ensure that enough contact is made between the chemical and the lesions.

The key is to put these in high traffic areas where the calves must walk through them with enough access to make recharging the bath easier. Minimizing the amount of manure on the feet will also decrease the organic material tracked into the footbath and make the solution last longer. 

The frequency and solution of the footbath selected will vary depending upon the cattle handling facilities, safety of the people working the cattle, and the percent of the pen that is affected.

Prevention still centers around the pen environment and avoiding negative impacts on the heel area of the calves. We have found that decreasing the moisture in the pen by more aggressive cleaning and decreasing animal density can be helpful. Scraping outdoor lots to remove manure and smooth out frozen hoof prints should improve foot health. 

Close observation of the feet of newly arrived cattle and recording their source can potentially identify problem sets of calves at arrival. Running cattle through a footbath at arrival should also be considered if active lesions are suspected in new cattle.