Source: Ontario Ministry of Agriculture, Food and Rural Affairs
Digital dermatitis is a painful foot condition causing lameness. The disease has been associated with several different bacteria, primarily a group of bacteria called Treponema spp. These bacteria survive best in wet or muddy conditions and the disease is highly contagious once an animal in a group becomes infected. Prevention and control of the disease depends on prompt detection and treatment of affected cattle.
What is digital dermatitis?
Digital dermatitis is an infectious disease of cattle. It was first identified in dairy cattle in the 1970s, but the cause of disease was not initially clear. Numerous microorganisms have been identified on the surface of lesions, many which may be associated with the environment, the lesions themselves, or both. The resolution of lesions in response to treatment with antibiotics suggested a bacterial cause. The disease is now recognized to be polybacterial, meaning multiple bacteria must be present to produce the condition. Substantial evidence exists that several species of the bacteria Treponema from the spirochaete family are consistently associated with disease. Other bacteria may be involved to facilitate colonization of the skin and lesion development. The profile of bacteria associated with lesions may differ between farms and change overtime as the lesion progresses.
The disease is characterized by painful lesions on the feet. Initially, lesions are raw, red, circular ulcers with a strawberry appearance, hence why the disease is sometimes referred to as strawberry foot-rot. Typically, lesions occur on the back of the foot, just above the heel and are more common in the hind feet. Chronic lesions may extend up in between the claws and develop hair-like projections with a warty appearance, thus another common name for the disease is hairy heal wart. A scoring system is used for lesions to describe stages from new active lesions, to healing or chronic lesions. The progression of lesions is often associated with increasing severity of lameness. The disease is highly infectious once an affected animal is introduced to a naïve group, although new infections may not be initially apparent as the lesions are slow growing and develop over several months.
The disease is mostly found in cattle kept in confinement, and globally is found frequently in dairy cattle. Identification of the disease in beef cattle has increased over the last decade. Feedlot animals are at greater risk due to confinement. Typically, heavy cattle close to marketing are most often affected. Cattle that are severely lame may display signs such as shifting weight between legs or walking on toes to avoid pressure on the lesions. The severe pain associated with infection makes it an important animal welfare issue for cattle.
Diagnosing Digital Dermatitis
Generally, a diagnosis of digital dermatitis can be made based on the history and signs in the herd. Cattle will need to be restrained in an appropriate foot chute to examine feet closely and visualize the lesions. Once the characteristic lesion is observed, a diagnosis is easily made.
Economic impacts of digital dermatitis
Studies to assess the impact of digital dermatitis have been undertaken in dairy cattle where negative effects on reproduction and milk production losses have been reported in addition to treatment costs. There has been little such research in the beef sector. One 2017 research study reported the presence of active digital dermatitis lesions negatively impacted growth performance, final live weight, and hot carcass weight in finishing beef cattle.
Prevention and management of digital dermatitis
Muddy or wet conditions and purchasing animals are the two most common risk factors for the development of digital dermatitis. Although bacteria are ubiquitous in cattle and the environment, of the more than 20 species of Treponema that have been associated with digital dermatitis, none are considered part of the normal bovine flora. Therefore, the introduction of these bacterial species typically occurs when affected cattle are purchased and mixed with unaffected animals. Other factors that can contribute to digital dermatitis outbreaks are high humidity and poor hygiene. Insufficient hoof trimming and the use of contaminated equipment has been associated with the risk of disease in research from dairy cattle.
Lesions may not be seen for 4 to 5 months after entry into the feedlot, consistent with the average amount of time lesions take to develop and coinciding with animals being ready for slaughter. The occurrence of disease in animals close to marketing can be particularly problematic. Residues may be incurred if lesions are treated with antibiotics or analgesics and transport of severely lame animals is inappropriate and prohibited.
Control of disease should focus on preventing risk factors as well as resolving the lesions in affected cattle. Prompt detection of lesions and efficacy of treatment can influence the severity of lesions. The most common form of individual treatment is the use of a topical antibiotic compound, either as a powder, paste, or spray on the lesion. There are few studies examining the appropriate dose of topical antibiotic, and treatment is considered off label. Historically, bandages have been applied after the antibiotic, but this may be counter productive if bandages quickly become soiled and manure and debris are trapped against the affected foot. This approach to treatment in feedlot animals is challenging because it is labour-intensive and a single treatment might not fully resolve the lesion. Lesions are often reduced in size and improvement in lameness score is noted, but long term, lesions tend to fail to completely resolve and become worse again. The susceptibility of bacteria to the most commonly used antibiotics (tetracycline or oxytetracycline) varies in research, and there may be poor response to treatment for some of the bacteria most prevalent in digital dermatitis lesions. Repeating treatment until a return to healthy skin has been achieved may be necessary.
Control of disease via group hoof disinfection is also used, typically by passing cattle through a footbath. Pulling individual animals with more advanced lesions for treatment can be done as previously discussed, while footbathing may control early lesions from progressing to more severe lesions in less obvious cattle and reduce transmission. A multifaceted approach is likely most effective for feedlots.
The most widely used chemicals in footbaths include copper sulfate, zinc sulfate, formaldehyde and antibiotics. Copper sulfate, although shown to be efficacious in research studies due to its antimicrobial nature and ability to harden hooves, is damaging to the environment. Human health concerns regarding formaldehyde, a carcinogenic compound, discourages its use. Several alternative footbath products have become available, some with limited evidence for cure rates similar to copper sulfate when evaluated in dairy cows. However other reports are only anecdotal or are poorly controlled studies, and research evaluating recurrence of lesions is generally lacking as are feedlot studies. However, the use of footbaths in feedlots is increasing. Moving animals through a footbath on arrival may help to control disease from animals that enter with digital dermatitis. Long, wide footbaths can allow multiple animals to walk through at a time and ensure each foot is exposed to the solution. Short, narrow footbaths can easily be avoided by cattle. The length of contact time required will vary by product, and label or veterinary directions should be consulted. Some products may require several minutes contact time. After foot-bathing, cattle should stand in a dry area so that the footbath solution can dry on the feet. For feedlots, there lacks a consensus for how often cattle should be using a footbath. Several times during the feeding period (monthly) has been suggested, and more often (weekly or bi-weekly) if cases are being diagnosed. The key to any footbath is changing the solution when it becomes soiled with manure to ensure efficacy of the foot bath solution.
Other management strategies have been largely unrewarding. Research efforts to develop a vaccine have not been successful to date. Mineral nutrition is considered important in general hoof health and lameness and should be evaluated, particularly if increasing prevalence of lameness in the herd. There is however little research identifying specific deficiencies associated with digital dermatitis or supplements to reduce the disease. To manage the disease, it is necessary to maintain lameness and treatment records. These should include the type of lameness (digital dermatitis or other diagnosed diseases), the treatment given, success, and usage of the footbath. This information can monitor disease prevalence and treatment success and inform future risk mitigation and control strategies.
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Author: Dr. Cynthia Miltenburg, Lead Veterinarian Animal Health and Welfare, OMAFRA