Acute active digital dermatitis lesions can cause pain and lameness in cattle. It can become a significant production problem and a serious animal welfare issue in both beef and dairy herds.
Digital dermatitis (DD) — also known as hairy heel warts, strawberry foot rot, raspberry heel, foot wart and hairy heel wart — first appeared in Italy in 1974. The disease then suddenly appeared in U.S. dairy herds in the 1980s and spread rapidly during the 1990s as herds expanded. Commingling of multiple dairy herds into one barn or facility provided the opportunity for DD to infect millions of cattle. A U.S. study in 2000 identified digital dermatitis in 29 per cent of culled dairy cattle at slaughter. Four per cent of culled adult beef cattle showed the same lesions.
While DD is most frequently seen in dairy herds, beef herds are no longer immune. Feedlot cattle are especially susceptible. The key to controlling DD is to prevent outbreaks and spread of the disease within herds once it appears. Commingled groups and animals assembled under stressful conditions are at highest risk of contracting DD. Bulls can be affected, rendering them unable to breed. Outbreaks have been reported in western Canadian feedlots.
The economic impacts of DD in beef herds include reproductive losses, treatment costs, labour inputs and costs associated with the premature replacement of reproductive females and bulls. Individual costs associated with cases in dairy animals exceed $100.
Digital dermatitis cannot be cured, only managed. Once infected with DD, individuals remain infected for life. The underlying cause of DD is a spiral-shaped bacteria called Treponema that gains entry through breaks in the skin on the foot. A cocktail of other bacteria found in damp, dirty conditions can predispose an animal to or complicate control of DD.
In 85 per cent of cases, digital dermatitis lesions occur on the back feet. Lesions can spread between the toes and sometimes appear on the front of the foot. Lesions vary in appearance. One type appears as raised callous areas. Active, growing lesions appear to have long fibrous hairs. DD lesions can also appear as raw, red, oval ulcers on the back of the heel just above or at the coronary band.
Raw skin lesions are incredibly painful, and cows will dramatically alter their gait and posture to avoid putting pressure on them. Animals will walk on their toes because the lesion is usually at the heel, which may cause the hoof on the heels to overgrow.
The disease is highly contagious and can spread rapidly and affect a large percentage of animals once introduced through the addition of new cattle into a herd. Younger cattle tend to be more susceptible, and cases in dairy cattle tend to occur around calving. This suggests that immune system suppression may play a role.
Treatment is difficult and usually requires cleaning and drying the lesion, then applying an antibiotic in a bandage or with a topical spray. Antibiotic sprays, which usually contain a tetracycline mixture, need to be applied twice daily — a practice feasible in dairies, but very difficult in a feedlot setting. Injectable antibiotics are often used in conjunction with topical treatments, but there is limited evidence that they are helpful.
Prompt treatment of active lesions will reduce the spread of DD to other cattle and reduce the chance of the infected animal’s development of lameness. Treatment requires the lifting of the foot, cleaning of the lesion, and applying topical oxytetracycline. Once a lesion has started to heal, topical dressings may be applied with a pressurized backpack spray unit. Soluble oxytetracycline or lincomycin-spectinomycin (66 g and 132 g/l of water, respectively) produces the best results. Older, non-active lesions are a reservoir for future outbreaks. Treponemes lie deep within the skin and can become active at any point.
Running cattle through a footbath two to three times per week should keep lesions in a chronic non-active stage. A premix, formalin, or copper sulfate solution will serve as an antibacterial and hoof-hardening solution.
Footbath solutions control the disease in dairy herds but can be difficult to manage in beef cattle. Cattle in settings where manure management is difficult should walk through footbaths twice a day for at least five days a week, something very difficult to achieve in feedlots.
Once-a-week footbaths may be sufficient in more hygienic conditions, which is more practical in beef cattle herds. Producers should consult a veterinarian before starting a treatment program. Footbaths require considerable effort to manage and need to be long enough and deep enough to allow each foot to be submerged twice.
Researchers are attempting to create a vaccine, but results have not been promising.
The disease spreads rapidly from newly acquired animals. It can be introduced by mechanical vectors such as boots or hoof trimming instruments. Hoof trimmers should disinfect their equipment between farms to avoid spreading this highly contagious disease.
Producers can attempt to prevent bringing digital dermatitis into their herds by avoiding contact with infected dairy cattle. Keeping areas where cattle are kept as clean and dry as possible is a good start to prevention.
Prevention requires good hygiene and pen conditions by reducing stocking density and avoiding mud and manure accumulation around watering and feeding areas. Since already-infected calves do arrive at feedlots, everyone in the beef supply chain, including cow-calf and stocker operators, should be aware of the disease and its potential consequences.