What is Digital Dermatitis?
Digital dermatitis is a skin disease of cattle, which usually affects the skin on the bulbs of the heel. Digital dermatitis can also be found between the digits or in the area of the coronary band. It can also affect other foot lesions such as sole ulcers and interdigital growths causing considerable pain.
Even mild digital dermatitis causes significant damage to the skin and, as it progresses, the affected area expands and the depth of tissue damaged increases. If digital dermatitis is not treated it can persist for months. Although each individual case of digital dermatitis costs less than a case of sole ulcer or white line disease, because the disease is infectious and spreads between cows the total cost of digital dermatitis on-farm is often more than that from other causes of lameness. Treatment and control of digital dermatitis is essential on economic and welfare grounds.
Cattle with digital dermatitis may show signs of lameness when standing or when moving. The most commonly seen presentation is the standing animal that flicks its foot repeatedly for no obvious reason. However, a very high proportion of cattle with digital dermatitis may show no signs of lameness (up to 90% if routine treatment is used).
Digital dermatitis is very painful, and the majority of cows with digital dermatitis will withdraw the foot rapidly if pressure is applied to the affected area (such as water pressure from a hose).
Looking at the feet
Classical digital dermatitis is fairly easy to diagnose if you have seen it before. If you have not seen it before then you should contact you veterinarian to confirm it.
There are five stages in each lesion:
1) The paintbrush lesion: a few matted hairs – this is rarely seen
2) The pink lesion: loss of hair and skin damage – fresh cases will show these signs
3) The red lesion: more severe skin damage – active painful lesion
4) The white lesion: longer-term lesion, with skin producing white keratin plugs – most cases will look like this on farms which have had digital dermatitis for a while
5) The black lesion: Production of a scab over damaged skin – the lesion looks healed but, particularly if digital dermatitis is not controlled on farm, new red lesions can start in previously scabbed areas
However, not all lesions of digital dermatitis are classical, so to confirm whether lameness is due to digital dermatitis you need to check around the coronary band and between the digits. ‘Hairy warts’ which occur in very long-standing digital dermatitis cases and are commonly seen in the US are rare in the UK. If you are not sure get a veterinarian to examine the cow.
There are three treatment options:
1) Individual application of antibiotics to the damaged skin
2) Herd treatment via an antibiotic foot-bath
3) Herd treatment via a non-antibiotic foot-bath
The decision as the best treatment is complex and should be discussed with your veterinarian, but there are several important points to consider:
i) The most effective treatment is individual treatment with antibiotics.
ii) Herd treatment treats animals with digital dermatitis which are not lame and may not otherwise be treated so can form a useful part of a control strategy
iii) There are no licensed antibiotic foot-baths thus their use legally requires a 7 day milk withdrawal. This is particularly problematic if whole herd treatment is needed
iv) Formalin and copper sulphate footbaths have both been shown to be as effective at treating digital dermatitis as antibiotic footbaths
v) There are many claims for other products but little evidence of effectiveness. Ask your vet for advice before using an alternative treatment.
As the NADIS data shows, housing is a major risk factor for digital dermatitis, although cattle at pasture can still get digital dermatitis, particularly if the weather is wet. This is because contact with slurry is essential for the development of digital dermatitis. Thus prevention of digital dermatitis is based on two strategies:
1) Reduction in contact with slurry
2) Early diagnosis and treatment of all cases of digital dermatitis.
A) The method of scraping can have a large impact on the amount and severity of digital dermatitis. Automatic scrapers have been shown, in an MDC-funded study, to increase the proportion of cows with digital dermatitis by around 30%, and the severity by 20%. Other areas such as collecting yards can also spread digital dermatitis, so attention needs to be paid to these.
B) Herd footbathing can be a useful method of control as all cows even those with small or early lesions cows are treated. Antibiotic footbaths have been commonly used for this purpose but they should only be a last resort not the primary method of control. Non-antibiotic alternatives are cheaper and can be just as effective. On some farms daily footbathing may be necessary.
C) Digital dermatitis is more common in housed animals but does occur in cattle at grass. It is thus essential to control digital dermatitis before the cattle are housed. If cattle are treated at housing, the amount of digital dermatitis in the herd can be significantly reduced and the increase during the housing period significantly diminished.