To reduce the rate of culling
Left uncontrolled, the prevalence of sheep with lesions may be over 50 per cent during early summer, often in cases of mixed infection with ‘S’ (virulent) and ‘U’ (benign) strains. Five-day foot bathing can minimise score 1 and 2 footrot lesions associated with these strains, with little or no culling. When applying five-day bathing in this situation, allow enough time between treatment and the summer eradication inspection, according to procedures recommended by your stock inspector.
Detection of lesions after treatment
Five-day foot bathing at pasture senescence does not interfere with the detection of lesions six weeks after treatment. Lesions were observed within two weeks after five-day bathing in an experimental flock infected with a highly virulent ‘S’ strain. However, it was impossible to predict which individual sheep would have lesions after the foot bathing. Flocks infected with low virulence ‘S’ strains of D. nodosus showed no lesions in the six weeks after bathing in early summer or in the following spring.
Factors affecting topical treatment of footrot
Environment, host resistance and virulence of D. nodosus strains are the major factors affecting the severity of lesions and the effectiveness of topical treatments. The deeper the lesions, the lower the chance of successful foot bathing. D. nodosus can persist in deep covert lesions for many months.
Environmental features that help summer eradication also increase the success of five-day foot bathing.
- Footrot can self-cure on dry or sandy, well-drained soils.
- The chance of footrot eradication increases in hot, dry summers.
- Footrot was not eradicated from a sheep flock chronically infected with mild ‘S’ strains of D. nodosus when the sheep were placed on wet, lush pasture after five-day bathing.
Sheep with foot abscesses can harbour the footrot bacterium without showing typical footrot lesions. There is no guarantee that D. nodosus harboured in foot abscesses will be successfully treated by five-day bathing. Abscesses surrounded by thick scar tissue interfere with the footrot treatment.
Other aspects to consider:
- Placing treated sheep on wet or lush pastured environments will greatly reduce the success of five-day foot bathing. Allow feet to dry out on grating or similar overnight between each treatment.
- Foot bathing solutions must be topped up daily and be free of mud.
- Mis-mustering can undo all the benefits of foot bathing treatments.
- Failure to adhere to the treatment protocol increases the risk of breakdown.
Protocol for five-day foot bathing
The feet of all sheep are examined by an experienced inspector and lesion scores recorded in the week before five-day foot bathing.
- All sheep with greater than score 2 lesions, foot abscess or abnormalities as listed in the 'Farmer’s Guide to Eradication’ are culled from the property before bathing.
- Treat only sheep with score 0, 1 or 2 lesions.
- Prepare the foot bathing solution by slurrying 20 percent zinc sulphate heptahydrate plus wetting agent in a drum for 24 hours to dissolve.
- Bathe the sheep in the solution, covering the coronet of the foot, for ten minutes each day.
- Monitor the strength of the solution daily with a Zinc Sulphate Footbath Hydrometer (Nufarm, Victoria).
- Use the same solution for five days, if it is not too dirty, topped up daily with extra chemical to maintain concentration and volume.
- Carry out the foot bathing in a dry environment, such as on grating, to maximise uptake of zinc in the horn. Mud overloads the bath with organic matter that binds and inactivates zinc sulphate.
- Time the daily foot bathing of the mob of sheep so they are on the slats of a shearing shed overnight or a pen with dry sandy soil, or graze a pasture paddock that is completely hay-off. This action prolongs the desiccation effect of zinc to dry the surface of the interdigital skin. The triple action (disinfection, short and longer-term desiccation) is how the daily foot treatment eventually overcomes the D. nodous bacteria’s ability to survive in the ruminant hoof.
- Dispose of the foot bathing solution according to local regulations.
- After foot bathing, keep the sheep on dryland conditions.
Livestock, machinery, fodder and people can introduce animal and plant diseases, weed seeds and pests. Develop a biosecurity plan for your farm to reduce the risk of these problems.