26 April 1996

LAME CURSE IS WITH YOU FOR KEEPS…

Dont expect the commonest cause of lameness to disappear at turnout. Jessica Buss reports that once youve had it, youve got it for good

What is DD?

Digital dermatitis is a lesion found in front or behind the interdigital space. It is mostly seen at the heel, and can spread over the bulbs of both heels. It is initially confined to the surface of the skin. The outer layer erodes and exposes an underlying granular red area. This looks angry, inflamed and weeps.

Interdigital dermatitis occurs between the claws in the interdigital cleft and should not be confused with digital dermatitis. However, DD can affect the skin on the area of the coronary band at the top of the hoof, especially at the front adjacent to the interdigital cleft.

Disease is linked with poor foot hygiene. It was first reported in the UK in 1988, but Dr Murray has a photo of a case in 1982 that was mis-diagnosed as a heel ulcer.

DIGITAL dermatitis is now one of the commonest causes of lameness in some herds. It is an infectious disease that is on the increase.

Cases have been reported from Cornwall to the Shetland Islands, according to Liverpool vet schools Dr Richard Murray.

He estimates it now costs the dairy industry £10-12m a year with a typical 100-cow infected herd spending over £2000 in vet fees, drugs, withdrawal of milk from severely affected cows requiring injection, and control measures.

Dr Murray cites a Liverpool vet school study of lameness incidence that shows digital dermatitis accounts for 40% of skin lesions that cause lameness and 20% of all lameness is caused by skin lesions. However, incidence varies from region to region. In Cheshire DD accounts for 47% of the lesions but in the Wirral it is lower at 23%.

"It is now the most commonly diagnosed skin lesion," he says. However, a cure is one step closer following the discovery of what causes it.

Blood samples from 1200 cows have shown that it is due to an organism called a spirochaete. Leptospirosis in cows is an example of a spirochaete infection, as is Lyme disease in horses and dogs. However, Dr Murray admits further studies are needed to identify the specific spirochaete that causes digital dermatitis.

"We suspect the organism lives in the environment in cow slurry and then spreads to other cows," he says.

"We need to identify what it is to establish an effective means of treatment," he says. "Until then we will continue to throw large amounts of antibiotics at it and hope that they have some effect.

"These treatments are effective and will achieve limited control in the event of a herd outbreak. However, they fail to eradicate the disease." The upshot is that new cases will keep occurring once the infection is present in the herd.

"Infected herds rarely eradicate the disease even by culling infected cows," he says. Once cows have been infected they become immune to further infection. But the organism is present on the skin to transmit to susceptible animals, such as heifers or purchased cows entering the herd.

Dr Murray recommends removing muck and straw off the foot, cleaning away dead tissue using surgical spirit on cotton wool and treating with topical antibiotics prescribed by the herds vet. Foot-bathing with antibiotics or copper sulphate will then help control the disease. However, he acknowledges foot-bathing is not a cure and that it squanders expensive antibiotics that could have other more vital uses. Foot-bathing solutions are also difficult to dispose of acceptably.

New environmentally friendly agrochemicals need to be developed with a carrier to penetrate the skin, he claims.

Although it is considered the curse of winter-housed cattle, last summer Dr Murray saw cows infected after turnout last year. He attributes this to the wet spring. It is likely that when a cow is infected the organism remains on the skin throughout the summer and such a cow is capable of passing it on at housing.

Severely infected herds may wish to footbath through the summer. Dr Murray recommends using a 5% copper sulphate solution fortnightly.n


&#8226 Costs typical 100-cow infected herd £2000/year.

&#8226 Caused by spirochaete infection.

&#8226 Can affect cows after turnout.


DIGITAL DERMATITIS

Although initial infection is confined to the outer skin, neglected cases can be much worse. Dont confuse it with interdigital dermatitis, which occurs between the claws. No case ever needs to become as bad as this.

An all too common sight on an increasing number of farms. It usually occurs in front or behind the interdigital space, most often at the heel.

Immune cows with healthy-looking feet can harbour DD infection.

Dr Richard Murray is working to establish exactly which spirochaete organism is responsible for a plague now costing farmers £10-12m/yr.