Super-rot fears grow
ASEVERE form of foot-rot, now being referred to by vets as new virulent foot-rot, has been identified in several commercial flocks.
This new, aggressive form of disease, unless treated, can quickly cause permanent damage to the foot, leaving culling as the only option.
Liverpool University sheep vet Agnes Winter first saw the disease last year. The flock had been plagued by a persistent foot-rot problem for some time. When Dr Winter was asked for her opinion she recognised a severity of infection not seen before.
"My initial reaction was that it was by far the worst case of foot-rot I had ever seen. Feet were intensely inflamed; foot-rot we normally encounter does not cause such severe inflammation unless there is a secondary infection.
"In this case, feet, and often well above the hoof, had become extremely swollen. The horn part of the hoof was rapidly becoming undermined by the level of infection," says Dr Winter.
While the ordinary form of foot-rot may be severe – depending on the strain of bacteria involved – it usually responds to treatment. The foot will recover and horn growth will regenerate downwards from the band.
But in some of the worst cases of the new, virulent strain examined by Dr Winter, horn damage had been so severe that re-growth was impossible. "In fact in some cases the horn had fallen off completely. The foot-rot we normally see does not usually destroy the foots ability to regenerate new horn once infection is under control."
Infected sheep from the flock in which the disease was first seen by Dr Winter were treated in three ways: One group of sheep treated in the foot-bath containing a 10% zinc-sulphate solution (one treatment of five minutes a week over four weeks); another group was given a single intra-muscular injection of long-acting oxytetracycline and a third group was given a single injection of a combined penicillin and streptomycin at double the recommended dose.
Dr Winter says she was surprised at the response to the zinc sulphate solution which improved the infection even after the first treatment. The injection of oxytetracycline (1ml for every 10kg bodyweight) was also successful in bringing the infection under control.
The cause of this new form of foot-rot, which has also been recognised by other vets, has not yet been identified. Samples of infected tissue tested at MAFF vet investigation centres have suggest that the disease may be linked to the cattle foot disease digital dermatitis.
No previous significant links have been identified to suggest that foot-problems can spread from one species to another. Because this new form of foot-rot is still in its early days of veterinary investigation, vets have no firm evidence to suggest a new link between lameness in cows and sheep.
But there is a difference between bacteria normally associated with foot-rot and a type seen in the new strain. A spirochaete, a bacterium that can penetrate the skin surface and is more usually linked with digital dermatitis in cattle, has been identified.
Dr Winter says that early treatment of sheep infected with the virulent strain of foot-rot is essential. "Sheep which are neglected because a farmer does not realise just how serious the problem is are likely never to fully recover.
"Certainly some of the cases I saw had suffered such serious damage to the feet that they would end up as casualty sheep and have to be destroyed."
Dr Winter warns that the disease is potentially very serious. Sheep producers must be aware of this new virulent form of foot-rot and how easily a flock can be infected via bought-in sheep carrying the disease.
She advises carefully checking feet of all bought-in sheep, and giving a routine foot-bath treatment to all new arrivals. Sheep brought on to a farm from another flock should always be isolated from existing stock; farmers should be satisfied that they pose no risk of infection before introducing them to the main flock.
"It is very easy to inadvertently buy-in this severe strain of foot-rot which could quickly spread to the whole flock. More cases have now been identified and careful checking of newly bought sheep is a must to avoid what could be a very costly problem," she warns
Dr Winter advises farmers with flocks with a persistent foot-rot problem and who feel they may be dealing with the new virulent strain, to contact their vet to decide upon the most appropriate treatment.
"And unlike conventional foot-rot where some careful trimming of the hoof is advantageous, in the case of the virulent form no trimming must be attempted. The hoof is far too inflamed and trimming would be too painful."
Graham David, MAFF senior veterinary investigations officer based at Shrewsbury vet investigation centre, has been involved in the early bacteriology work concerning the new foot-rot disease.
"Its still early days to prove a link between cows and sheep but the spirochaete bacteria that have been identified in the new foot-rot have also been found in digital dermatitis cases.
"Work in the USA claims to have re-created the new virulent form of foot-rot from spirochaetes but there is still along way to go to prove the association between acute foot problems in cows and sheep," says Mr David.
Wet weather during this years grazing season makes
prospects of lameness and foot-rot this winter more
likely, undermining performance and creating a serious
welfare problem. Jeremy Hunt kicks off this special with
a look at the discovery of a new virulent form of foot-rot.
Edited by Simon Wragg
• Intense inflammation.
• Severe horn damage.
• Early treatment vital.