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Foot rot - Note 3

Foot-Rot

Lameness in sheep is a major cause of significant pain and suffering in sheep which also corresponds with production losses. The lameness associated with foot-rot reduces the ability of a sheep to graze which leads to a failure to thrive, depressing lamb liveweight gain by up to 100g per lame foot per day and lengthening the finishing period. In the case of ewes the resulting poorer condition score is a major contributory factor to increased rates of barren ewes or lower conception rates.

Diagnosis

Before tackling any lameness problem it is important to get the diagnosis right. Outbreaks in flocks tend to occur after prolonged damp, warm weather. Flocks which are kept at a high stocking density tend to have a higher proportion of sheep affected by foot-rot. If foot-rot is present in the flock several sheep may be showing signs of severe to moderate lameness. On closer inspection, there is swelling and wetness between the claws of the foot as well as inflammation of the skin-horn junction. Although these initial signs are also typical of scald, a condition which is more easily treated, true foot-rot is distinguished by under-running/separation of the horn from the claw. This is because one of the bacteria involved, Dichelobacter [Bacteroides] nodosus, can liquefy horn at the skin horn junction. The survival of Dichelobacter nodosus on pasture, in the absence of sheep, is the key to eradicating foot-rot from your flock.

Treatment

If control is to be successful it must be dealt with on a flock basis. Infected sheep are the source of infection for other sheep and pasture which has been free of sheep for at least 10 to 12 days will no longer harbour the causative agent. Therefore a succession of clean pastures (that is, land free of sheep for the previous ten days) will need to be available in order to properly tackle this disease. Eradication requires a concerted effort over a 20 day period and is most likely to be successful if the weather is warm and dry. An ideal time to dedicate to the footcare of your flock is therefore post weaning and pre tupping. Your veterinary surgeon is best placed to advise on the feasibility of adapting the following programme for your flock:

DAY 1

Examine all feet and divide the flock into two groups; sheep which are showing signs of foot-rot are designated as the hospital group and the sheep with healthy feet are designated as the main flock. The main flock should then be allowed to stand in a foot-bath of 10% zinc sulphate for 20 minutes and moved directly to clean pasture. The hospital group should always be treated after the main flock and may require an injection of long acting antibiotic under guidance from your veterinary surgeon. Any hoof clippings should be removed and destroyed and the pen cleansed and disinfected. Over the following 20 days the treatment schedule may be as follows:

Hospital group:

  • Treat by paring, footbathing, antibiotic injection (as necessary and move to clean pasture).
  • Field 1 - Day 5 Re-examine and treat group as above.
  • Field 2 - DAY 10 Re-examine and treat group as above. Lame sheep from main flock join hospital group.
  • Field 3 - DAY 15 Re-examine and treat group as above and move to clean pasture (Note field 1 is now considered "clean").
  • Field 3 -DAY 20 Re-examine, footbath sound sheep and add to main flock
  • Result Cull remaining lame sheep.

Main flock:

  • Footbath and move to clean pasture.
  • Field 4 - DAY 10 Re-examine flock and footbath. Sound sheep from hospital group rejoin main flock.
  • Field 5 - DAY 20 Re-examine and footbath
  • Result Clean Pasture

Note:

The bacteria that causes foot-rot cannot survive in the presence of oxygen so healing is helped by paring. However, over-paring can exacerbate lameness and it is a better policy to provide adequate contact time with zinc sulphate. Inclusion of washing-up liquid to produce a frothy consistency in the foot bath will assist with the penetration of zinc sulphate.
Foot-rot vaccines are available which may help to reduce the occurrence of the disease in your flock and can be considered along with the other control methods mentioned above. Relying solely on vaccination will not eliminate the condition. Again, consult your local veterinary surgeon for further advice on this matter.
If your flock has no foot-rot problems, then beware of buying sheep which have foot-rot and could thus be a source of infection. Straying sheep may also carry the infection which is another reason for maintaining secure hedges and fences. Currently there is a particularly severe form of foot-rot spreading through sheep flocks in Great Britain, so be extra vigilant of sheep originating from outside Northern Ireland. It is good practice to keep any bought-in sheep separate from the main flock for at least two weeks. During that time, pare and examine the feet of these newcomers and treat any infection accordingly. Do not forget that rams and goats can carry this infection too!

Key Facts

  • Foot-rot is caused by a bacterial infection and is introduced and spread around the flock by infected sheep.
  • The bacteria responsible can survive on pasture for 10 to 12 days so treatment and rotational grazing are the key to controlling foot-rot.
  • Cull severely affected animals.
  • Introduction of new stock to the flock can introduce diseases such as foot-rot.