There are two main forms of footrot in sheep and goats: virulent and benign. Both forms are caused by the bacterium Dichelobacter nodosus.
The signs of benign footrot (also known as ‘foot scald’) are often milder than for virulent footrot, but it cannot be distinguished from virulent footrot without laboratory testing so it is important to contact a Department of Primary Industries and Regional Development (DPIRD) veterinarian or biosecurity officer to take samples if you suspect your stock have footrot.
What is benign footrot?
Benign footrot can cause varying degrees of damage to the horn of the foot in sheep and goats, leading to lameness, while loss of body weight and wool production are minimal.
There are no quarantine restrictions for benign footrot.
Benign footrot can be clearly distinguished from virulent footrot by a laboratory test called the gelatin gel test on scrapings taken from skin or horn between the toes.
Inspections for virulent footrot are carried out in abattoirs and on farms. Flocks found with virulent footrot are quarantined to stop the spread of infection and advice is given to owners to help them either eradicate or control the disease.
Read more about virulent footrot [1].
How is benign footrot diagnosed?
Protease enzymes produced by the footrot bacteria break down the hoof wall. The gelatin gel test measures the stability of the protease enzymes when exposed to heat. The bacteria which cause virulent footrot are known as stable (S) strains and those that cause benign footrot are known as unstable (U) strains.
Signs of virulent and benign footrot
Virulent footrot has the potential to cause a more severe disease, whereas most benign strains cause a milder form. The clinical signs vary in severity, depending on:
- the susceptibility of the animal
- the environmental conditions
- the strain of bacteria.
Severe changes such as separation of the hard horn of the inside wall, sole and toes may result if:
- a sheep is vulnerable to infection
- there are moist, warm conditions
- a virulent strain of the bacteria is present.
Virulent footrot is not always severe. Less severe forms of virulent footrot may involve only the soft horn of the inside wall and the sole with early changes including moisture, reddening and loss of hair between the toes. These minor lesions are also seen with benign footrot.
A flock may have both virulent and benign strains of the bacteria present at the same time.
Species affected
Benign footrot is more severe in goats than in sheep and leads to minor lameness. Benign footrot strains commonly occur in cattle, which may be an important reservoir of infection for sheep. In rare circumstances, cattle can also act as a carrier for virulent footrot.
Other foot conditions
Footrot is relatively easy to distinguish from other foot conditions such as foot abscess (swelling of the foot; presence of pus) and scabby mouth (scabs on the lower leg above the foot as well as on the lips). However, more than one disease may be present in the flock, making it necessary to carefully inspect several animals to determine if footrot is present.
Note that lameness is the key sign of the exotic disease foot-and-mouth disease [2] in sheep. Detecting an exotic disease early is vital to reducing its damaging impacts on industry, so it is important if a number of sheep are lame to call a veterinarian [3].
When does footrot occur?
The factors which influence the spread of benign footrot are similar to those for virulent footrot: warmth and moisture. Look for benign footrot at the same times of the year as virulent footrot — mainly during spring but also in warm, wet autumns.
Impact of benign footrot
Benign footrot may cause lameness in sheep but this is short-lived and is usually only seen during spring. With hot, dry conditions the feet dry out and lameness and lesions disappear. Benign footrot does not usually cause severe production losses on a flock basis.
Restrictions on sale of sheep
When sheep with signs suspicious of footrot are seen at saleyards, they must be withdrawn from sale and handled as if they have virulent footrot. It is usually not possible to distinguish virulent and benign footrot visually. The inspector will collect and send samples from the sheep to the laboratory for testing. This takes about 10 to 14 days.
Farmers whose flocks have been adequately checked and only have benign footrot can negotiate private sales. Check your sheep carefully for signs of footrot before sale. If your property has a history of benign footrot and laboratory tests have been negative for virulent footrot, remove sheep with moisture or reddening of the skin between the toes from sale lines and only offer sheep not showing signs of benign footrot for open sale.
Use the National Sheep Health Declaration [4] to make a declaration that sheep in the consignment are free of virulent footrot.
Preventing introduction of virulent and benign footrot
Buyers need to ask the vendor for a National Sheep Health Declaration [4] and check sheep for signs of footrot before purchase. Isolate introduced sheep from other mobs for as long as possible, preferably until they have gone through the next spring when footrot will be more readily found if it is present.
The National Sheep Health Declaration does not guarantee freedom from disease, but does give useful information which helps buyers to make informed decisions when purchasing stock. It is important to note that agents cannot make the declaration on behalf of clients.
Industry Funding Schemes
Industry funds the Western Australian virulent Footrot Control Program via the Sheep and Goats Industry Funding Scheme. Read more about the Industry Funding Schemes [5].