- Digital dermatitis is a bacterial infection on the feet of cattle.
- It is increasing in New Zealand.
- To prevent your stock getting digital dermatitis, avoid buying cattle from farms with the infection.
- Ensure transporters disinfect stock crates and disinfect on-farm equipment.
- Improve slurry management and focus on reducing faecal contamination of feet.
- Check rear feet frequently for signs of digital dermatitis.
- Housed cows present a risk, especially in cubicle housing.
- Feed pads and stand-off pads should drain well and be cleaned regularly.
Digital dermatitis - a global issue now affecting New Zealand dairy herds
Digital dermatitis was first identified in Northern Italy in 1974, and has now been reported across the world. The first New Zealand case occurred in 2004, with sporadic reports until around 2011 when the number increased markedly. In a study in North Taranaki in 2015, two-thirds of the 224 herds visited had at least one cow with digital dermatitis. New Zealand dairy farmers need to be prepared for digitial dermatitis; to know how to prevent the disease getting on farm, and how to diagnose and control it if it does.
What does digital dermatitis look like?
Typically, digital dermatitis is found on the skin just above the interdigital space (Figure 1); however, it can also be found along the coronary band (Figure 2). Digital dermatitis is most commonly found on the hind feet; fewer than 3% of affected cattle have lesions on the front feet only.
The classical lesion of digital dermatitis is a moist ulcer (Figure 1). However, digital dermatitis is a cyclical disease with lesions forming, healing and then returning, so it has multiple stages. The most persistent stage (often called M4; Figure 1B) is a chronic thickening of the skin with rapidly spreading growths, which can often resemble hairs (in some countries these are called hairy hoof warts). In New Zealand, the most common appearance of digital dermatitis is a small lesion less than 1 cm in size (R. Laven, unpublished data; Figure 3).
Larger lesions, either when they develop into ulcers or when they are growing, tend to be extremely painful. Affected cows will often stand with only the tip of the toe touching the ground with the heel bulb raised, and may shake the infected foot repeatedly, while others might only appear lame when walking. However, many cows with visible digital dermatitis lesions show no sign of lameness and the lesions do not appear to be painful.
What causes digital dermatitis?
The current consensus is that treponemes are the primary bacteria responsible for the development of digital dermatitis. Research indicates that prolonged standing in wet, dirty conditions that result in softened and broken skin on the cow’s heel will increase the risk of digital dermatitis.
How to keep your farm digital dermatitis-free
The biggest risk of introducing digital dermatitis onto the farm comes from importing infected cattle, including replacement heifers and bulls. Cows or bulls should only be bought from farms that are free of the disease, as simply identifying and purchasing cows without visible lesions will miss carriers who are infected but do not have lesions. This is particularly important when purchasing groups of cattle; if one cow has visible lesions then the whole group must be rejected.
Whenever transporting stock between properties or purchasing digital dermatitis-free stock, ensure they don’t travel with stock from infected herds or in trucks that have not been cleaned effectively after carrying cattle of unknown status. Transfer of digital dermatitis can also occur via contaminated hoof trimming equipment, knives, ropes, buckets and clothing. Ensure they are disinfected before use and that footwear is clean.
Slurry the biggest risk
The treponemes bacteria found in digital dermatitis lesions are present in the gut of the cow and therefore, in cattle faeces and slurry. Slurry, which is a mix of urine, water and faeces, is the most potent means of spreading digital dermatitis because it contains both the treponemes and water; the latter moistens the skin and makes bacterial invasion easier. Urea (from the urine) breaks down skin keratin, allowing even easier entry for bacteria. Minimising contact with slurry is crucial to reducing the prevalence of digital dermatitis on-farm. Cows with clean, dry feet have a lower risk of digital dermatitis.
Housed cows more susceptible
The number of dairy farms in New Zealand that house cows for a significant proportion of the year is small (about 530). However, housed cows can act as incubators for digital dermatitis, building up higher levels of infection that can spread through transfer of cows between farms. If the number of cows housed in New Zealand increases, the risk of this spread will also increase.
Cubicle housing high risk
In New Zealand, there are more than 60 farms using cubicle housing, which is known to have a particularly high risk of digital dermatitis.
If houses have concrete flooring, farmers should at least monthly, during milking, examine the hind feet of all cattle for signs of digital dermatitis.
Cattle loose-housed in straw yards have a lower risk of digital dermatitis as there is less contact between slurry and feet in loose-housed systems1.
Clean stand-off and feed pads
Around a quarter of New Zealand farms (24%) use stand-off or feed pad facilities. Slurry control for concrete stand-off/feed pad facilities is often poor, with cleaning of these areas often being less than once a week, despite intensive use. If infected cattle are present on such farms, then spread of digital dermatitis will occur via the stand-off/feed pad facilities. For infected herds, concrete areas should be cleaned at least once every 12 hours; this will minimise the build-up of slurry and the risk of spreading digital dermatitis. Another key feature is drainage. Wet slurry, as discussed earlier, increases the risk of digital dermatitis. If the feed pad is poorly drained, it will need more frequent cleaning. Make good drainage a priority when building a new feed pad.
Slurry management is not just about housing and feed pads; collecting yards can also be an important source of slurry. Ensure that they are cleaned thoroughly after every milking.
If suspicious lesions are detected then veterinary advice should be sought to confirm it is digital dermatitis. Infected cows can be treated with a topical antibiotic spray. Antiseptic footbaths, used for every animal in the herd, can help control the spread of the disease.
For more information on practical measures to identify and manage digital dermatitis see the lameness section of this website.
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