Vet’s View with Iain Carrington: considering the three forms of foot disease in sheep
Lameness is one of the major welfare problems seen in the sheep industry, which can cause large losses in production if not dealt with properly.
There are three forms of foot disease which are often confused, but it is important to differentiate them so as to be able to apply the correct preventive measures and/or treatment.
Scald - a condition also known as Inter-digital Dermatitis or Benign Footrot - to begin with, is caused by the bacteria called Fusobacterium necrophorum.
This is probably the most common cause of lameness in sheep.
It is most usually seen when conditions are wet underfoot; lesions are found between the hooves with the inter-digital skin covered in a thin layer of white material or, when more severe, the area is red and swollen. There is no smell, and under-running of the hoof and sole are not seen.
If left untreated, it is a precursor to Footrot. Cases of Scald are reduced in drier conditions.
Footrot, meanwhile, is an extremely painful and contagious condition which occurs when the bacteria Bacteriodes nodosus infects a case of scald.
The hoof wall becomes separated and the sole is under-run, causing the hoof to deform. There is also a characteristic smell.
The bacteria is spread from infected animals and can only survive on pasture for up to about 12 days, so care must be taken with biosecurity and quarantine when purchasing replacement livestock.
Spread occurs primarily in warm, wet conditions.
In the warmer seasons, affected sheep are also more susceptible to fly strike.
Severely affected animals do not respond well to treatment and should be culled as there is a genetic susceptibility; it is wise not to retain the offspring of these animals for future breeding.
Selective breeding should allow for a general increase in resistance throughout the flock.
Finally, Contagious Ovine Digital Dermatitis was first described in 1997 and is a severe, painful condition associated with a spirochaete bacterial infection.
The condition has no inter-digital involvement and usually starts at the coronary band of the hoof on the outer wall, under–running down toward the toe leading to shedding of the hoof itself.
Hair loss extending 3 to 5 cm above the hoof is commonly seen and damage may be so severe that it affects the re-growth of the horn permanently.
Hopefully, these brief descriptions will enable you to differentiate these problems as they are found in your flock.
Footbaths are still a primary treatment and it is worth remembering the recommendations that go with this procedure.
Where possible, treat on a dry day. If feet are dirty, the sheep should be walked through water first and, after treatment, a dry standing of concrete or stones will improve the efficacy.
The use of an 8m long bath or, for some preparations, a stand-in bath is advised, with a move to clean pasture afterwards.
The use of 3% formalin or 10% zinc sulphate will control scald and prevent it turning into footrot.
The use of antibiotics topically or by injection should be discussed with your vet as part of your flock health plan.
At one time, foot-trimming was recommended as an aid to treatment, but in recent years it has been found to make matters worse.
- Iain R Carrington BVM&S MRCVS