Act fast to keep your cattle free of digital dermatitis
Foot hygiene and slurry management are essential components of keeping this painful condition - which can cause lameness and ultimately result in cattle taking longer to finish - away from the farm
Digital dermatitis is almost always lurking somewhere in the background of every farm. Also known as Mortellaro, the condition was once considered a dairy herd problem, but this is no longer the case. It now affects all types of cattle enterprises, resulting in cattle taking longer to finish, producing less and, ultimately, becoming less profitable.
Until recently the environmental reservoir of infection remained unknown until the presence of digital dermatitis-associated bacteria called treponemes was confirmed in cattle faeces and slurry.
Slurry is not only a reservoir of infection and provides a route of transmission between cattle, but is also very irritating to the soft skin of the heel, damaging its natural defences and leaving it more at risk of infection. If feet are heavily contaminated, it also creates the perfect oxygen-free environment in which the bacteria can thrive and cause infection.
If digital dermatitis comes into contact with intact, healthy skin, it is extremely unlikely to result in a lesion. Studies have shown that the only way to create lesions is by bandaging the foot and soaking them in water in order to create a warm, moist environment that will macerate the skin and provide ideal conditions for treponemes to survive and invade the skin. Therefore foot hygiene and slurry management are an essential component of digital dermatitis control.
Know the signs
There are many different stages to digital dermatitis skin infections. Even within these stages the lesions can vary in their appearance. Lesions mostly occur on the skin around the heels or between the claws but can occasionally be found at the accessory digits or on the front of the foot.
The six stages of digital dermatitis fit into a complex cycle of infection (see above). Uninfected cattle have normal, intact healthy skin around the claws with no sign of infection. When the skin's defences are weakened and damaged, usually through excessive exposure to slurry, it allows the bacteria to invade the skin, resulting in an early lesion. At this point the lesions are small (<2cm), are not usually painful and the animal doesn't show signs of lameness.
Unless the feet are regularly disinfected this lesion with continue to develop, growing in size and becoming a fully active lesion.
This is the classic red, raw, circular ulcerative lesion we associate with digital dermatitis infection. These are usually painful and the animal will show signs of lameness, in particular standing on its toes to shift the weight off the heels. If not treated with topical antibiotics at this stage, the bacteria move deeper into the skin, forming little cysts and the lesion becomes raised and 'strawberry like' in appearance.
Treatment with topical antibiotics will result in the formation of a firm scab over the lesion within 1-2 days, which is usually black in appearance. If treatment was administered early enough and is successful then the skin will return to normal once the scab has sloughed off. However, if treatment is delayed and the bacteria are encysted in the skin, then although the lesion has gone, the animal is still sub-clinically infected and at risk of the lesion returning.
Whilst treatments such as injectable antibiotics or topical copper sulphate pastes have been commonly used in the past, neither will produce a complete cure and, in the case of copper sulphate, there is some evidence to suggest that applying this direct to the lesion actually increases the risk of a chronic lesion developing.
Chronically infected cattle have no active lesions but the skin between the claws is no longer smooth as normal. Instead there is either thickening of the skin around the interdigital space, resembling a horseshoe shape (below right) or the lesion may appear as a 'hairy wart' with filaments of skin present. These are chronically infected cattle that are at risk of recurring and developing active lesions again, and are the key drivers behind outbreaks.
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