25 December 1998

Tackling foot-rot concerns

FOOT-ROT is a flock concern which means every sheep should be inspected. Chris Lewis, a specialist sheep vet, therefore warns that treating individuals for foot-rot is the least effective thing any producer can do.

"Gather all sheep and closely inspect every animal where you think you have a foot rot problem."

"No single factor will control this disease. For treatment and control, shepherds must recognise that attention to detail and many hours of hard work are necessary. In addition, pasture management must be such as to provide a succession of clean pastures which are free of foot-rot. This means no sheep for the previous 12 days."

Mr Lewis advocates producers follow a timetable (see panel) to control the disease within an infected flock. At gathering, sound sheep should be designated main flock. Lame and affected animals become the hospital group.

He recommends foot bathing in 10% zinc sulphate and an appropriate wetting agent such as ionic detergents or laurel sulphate. "Sheep should stand in this solution for at least 20 minutes. Where this is not practicable, stand for as long as possible, move and stand on a clean hard standing, such as concrete, for an hour and then repeat foot bathing," he advises.

"Sound, unaffected sheep can be foot bathed in 3% formalin – never stronger. Any concentration above 5% will do more harm than good as the inter-digital space will be damaged, allowing further infection."

Mr Lewis then recommends producers move sheep to clean grazing which has not carried sheep for 12 days. Another gather should follow after 10 days and the exercise repeated. At this stage any lame sheep must be transferred to the hospital group and the main flock again moved onto clean grazing. This should establish a nucleus of clean, foot-rot-free sheep.

"At first gathering of the hospital group, pare all overgrown feet and treat with antibiotics. My preferred treatment is 10cc streptopen which has a 60-day withdrawal period. Oxytetracycline at 20mg/kg which, if more virulent Fusobacterium spp are involved, probably controls secondary invasion better. Foot bath in zinc sulphate after the main flock and move to clean pasture."

The group should be re-gathered five days later and foot bathed. Only those which are still severely affected should receive antibiotics.

Five days from then, to coincide with gathering the main flock for a second time, foot bath sheep which are now sound and add them to the main flock.

Remaining lame sheep must be culled unless they are recent additions from a breakdown in the main flock. "Culling chronically infected sheep is a must if any long-term improvement is to be achieved. All evidence points to these sheep as the source of future outbreaks," says Mr Lewis.

Vaccines can play an important part in foot-rot control as they have both preventative and curative properties. "The initial thought is that they are comparatively expensive and may cause post-vaccine lesions. But used strategically they can be very cost effective by reducing the number of gathers and the amount of antibiotic and foot bath solution used.

"The sheeps immune system does not respond to invasion of foot-rot bacteria by forming antibodies, so never acquires any natural protection. However, the vaccine provides high levels of antibody, even after one dose. This means that vaccinating infected sheep leads to a cure, as well as providing protection against new infection. For best results use the vaccine in conjunction with conventional methods."

Good management also reduces the chance of foot-rot invading the flock. For example, close grazing and topping pasture reduces the chance of long stemmy grass encouraging scald. Mr Lewis also recommends producers lime muddy gateways and areas around troughs to raise the pH and hence discourage foot-rot bacteria. Always select foot-rot-free rams with good feet.

Eradicated

"With hard work and dedication foot-rot can be eradicated from a flock. Eradication programmes should not be started when disease is spreading, but in a dry period such as mid summer or a frosty time before housing.

"The approach is exactly the same as for treating an outbreak as shown in the table. Vaccinating and rigorous culling of permanently lame sheep or those with misshapen hooves markedly improves the chance of true eradication. Where a combination of vaccination and severe culling is practised, the whole process can be finalised in 15 to 20 days."

&#8226 SHEEP producers can attend one of 11 practical workshops on Reducing Lameness in Sheep. Part of a MAFF campaign, meeting venues are throughout England and Wales. Further details from Linda Tonkin at ADAS Wolverhampton (01902-693206).

Foot-rot treatment timetable

Time Hospital Group Main Flock

Day 0 Pare

Antibiotic < Clean Pasture > Foot bath

Foot bath

Day 5 Antibiotic < Clean Pasture

Foot bath

Sound sheep; foot bath, add to main flock >

Day 10 Antibiotic

Foot bath < Clean Pasture > Foot bath

Day 15 Antibiotic

Foot bath < Clean Pasture

Sound sheep; foot bath, add to main flock >

Day 20 Cull remaining Clean Pasture > Foot bath

lame sheep