About footrot in sheep
Footrot (or Dichelobacter nodosus) is an infectious and contagious disease that can potentially cause lameness in your flock. Ovine (sheep) footrot has long been dreaded by sheep owners.
Footrot of sheep and goats is a scheduled disease under disease control legislation. This means that:
- outbreaks of footrot must be notified to an Inspector of livestock within 7 days
- it is illegal to sell infected sheep or goats other than for slaughter
- it is illegal to place footrot infected sheep in or adjacent, to any saleyard or in any public place (including a road)
- infected sheep must be treated
- inspectors of livestock have the power to test and restrict movement of infected or suspect sheep and to ensure treatment is carried out
Strains of the bacteria
Dichelobacter nodosus (D. nodosus) bacteria are divided into a number of sub-groups, strains or serotypes identified by a letter of the alphabet. An outbreak of footrot may involve one or several serotypes.
It attacks by digesting the connective tissue between the horn and flesh of the hoof, and also under the horn of the foot.
The virulence varies widely between the various strains of bacteria. Most bacteria fall somewhere between the benign and virulent extremes.
For practical purposes the range is divided in two and each case referred to as either Benign or Virulent.
When assessing virulence by examining feet it is important to consider the environment of the sheep's foot and the time since infection occurred.
Benign footrot is bacteria of low virulence which have poor ability to under-run the hoof horn and mostly affect the skin between the toes.
Benign footrot can be controlled during the active stages by foot bathing. This may be repeated as often as required.
Moving sheep on to drier country is often sufficient to help recovery. However, the disease is likely to recur in the next favourable season.
If regular footbathing is required to control the disease then it is possible that virulent footrot is present and a different approach needs to be taken to treatments, control and eradication.
Virulent footrot bacteria rapidly under-run and separate the hoof horn from the foot.
Ideal environment for the bacteria
D.nodosus requires warm, moist conditions for ideal multiplication. The bacteria can only survive away from the foot for a maximum of 7 days, even in ideal conditions. In less favourable dry conditions, the bacteria die rapidly.
How the bacteria is spread
Spread is primarily from foot to foot via pasture or mud so moist pastures, laneways and muddy yards are the main areas where footrot is spread.
Footrot will therefore spread most rapidly when it is warm and moist, as in spring and some autumns.
What kills D. nodosus?
Footrot bacteria are readily killed by dry heat, sunlight, cold, dry environment and a number of different chemicals. Most domestic disinfectants will destroy D. nodosus but are not registered or recommended for treating sheep as they are easily de-activated by dirt contamination.
Zinc Sulphate, 'Radicate' and formalin (Formalin, Formol) are the chemicals currently registered for the treatment of footrot in footbaths.
Immunity to footrot
Sheep that have been infected with or exposed to footrot do not develop any significant natural immunity or resistance. Short term immunity can be achieved using vaccines.
Breed of sheeps susceptible to footrot
All breeds of sheep and goats can contract footrot, although British breeds are less susceptible.
- Foot shape and structure affect susceptibility.
- Goats are usually less severely affected, and may exhibit different symptoms to sheep infected with the same strain of bacteria.
- Merinos are often the most susceptible and severely affected.
- Low virulence strains are most severe in Merinos but are also seen in British breeds, goats and cattle.
- There are a few strains of sheep which are resistant to footrot but at present they are of no commercial significance.