If it is a sheep's most fervent ambition to die in the most dramatic way possible, then surely the next desire in its woollyhead is to go lame. For many U.K. flocks lameness is an endemic problem and prevalence has probably increasedfollowing the change in weather patterns to mild winters and wet summers. Lameness is an important source ofproduction loss and a welfare issue as well. Its prevention and control is time-consuming and requires a labour inputwhich is not necessarily readily available on today's farms.The two commonest causes of lameness in sheep, scald andfootrot are linked by a common cause, the bacterium Fusobacterium necrophorum, which is present in all ruminantfaeces and therefore on any pasture grazed by sheep.
Scald occurs when the interdigital skin becomes infected by this bacterium, causing inflammation and pain. Unlike infootrot, there is no under-running of the horn. Factors causing the development of scald include wet pastures and longgrass. These damage the interdigital skin and allow F. necrophorum to colonise the damaged area. Uncomplicatedcases of scald will resolve spontaneously if the sheep are moved to dry pasture. Alternatively individuals can be treatedtopically with oxytetracyline spray, or on a flock basis, by footbathing in 10% zinc sulphate or a 3% formalin solution.
Footrot vaccines are ineffective against scald.
Footrot starts as scald but requires the presence of an additional bacterium, Dichelobacter nodosus, which is foundonly on infected feet but can survive for 2-3 weeks on pasture.There are different strains of this bacterium which havevarying virulence. The combination of the two bacteria causes separation of the horn from the underlying structures ofthe foot. Depending on the strain involved, this separation may spread across the sole and up the wall of the hoof.
Anyone who has trimmed a diseased foot will know that the disease is associated with a characteristic foul smell,which tends to stick to the fingers! Treatment and control of footrot centres on footbathing, remedial paring, antibioticinjections and vaccination:
Footbathing in either 10% zinc sulphate or 3% (not stronger) formalin solution works well provided that the sheep arestood in the footbath for long enough (particularly important with zinc sulphate). Leave the sheep on hard-standing forat least one hour post footbathing and then ideally turn them onto fields that have been free of livestock for at least twoweeks and hence are clean.
Both of the bacteria involved in footrot are anaerobic and so paring the feet to expose the infected tissues to the air willaid recovery.Keep trimming to a minimum and do not to cause bleeding. Disinfect hoof-trimming equipment betweenanimals and sweep away hoof trimmings and dung from the trimming area between groups.
The footrot bacteria respond well to antibiotic injections such as Pen/Strep or Oxytetracycline. A single long-actinginjection will cure most cases of footrot, but is expensive on a flock basis and gives no protection against reinfection.
Vaccination is an important part of a footrot control programme. Vaccinate sheep twice,4-6 weeks apart, for maximumresistance and then give a booster dose before periods of maximum risk. Vaccination can also be used to aid recoveryfrom footrot, but vaccination alone will not control footrot on a farm and must be part of overall control programme.
Some sheep will prove impossible to cure and repeat offenders should be culled, as they will simply re-infect theirflock-mates. Susceptibility to foot rot is inherited and so do not keep replacements bred from ewes or rams that arerepeatedly lame with footrot
Isolate any bought-in sheep, or sheep returning from eatage for at least 3 weeks and inspect them regularly for signs oflameness.
Eradication of footrot on a farm is possible through application of the above regimes but attempts to eradicate thedisease under U.K. conditions which favour transmission of the disease often fail,and the cost of eradication can be
considerable and must be balanced against the cost of endemic footrot in the flock.
A relatively new cause of lameness is Contagious Ovine Digital Dermatitis or CODD. This serious infection of sheep'sfeet is characterised by lesions that begin at the coronary band and then rapidly spread down the hoof, often causingthe whole hoof to be shed leaving a raw stump. This condition fails to respond to orthodox treatments for foot rot andyou should seek veterinary advice if you think your flock is affected by this disease. On no account should affectedsheep be footbathed with formalin because of the painful nature of the lesions.
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