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Monday, 11 May 2015

Lameness Control in Sheep
Most outbreaks of lameness in sheep are caused by either scald (interdigital dermatitis) or footrot. These two diseases share the same primary cause, the bacterium Fusobacterium necrophorum; this bacterium causes damage to the superficial layer of skin between the claws and enables other bacteria to establish themselves. An important secondary bacteria, Dichelobacter nododus, causes footrot. The risk factors associated with these diseases are damage to the interdigital skin by exposure to moisture and mechanical trauma.

·         When underfoot conditions are wet, the most common cause of lameness in sheep is scald. On pastures, incidence of scald seems to be higher in lambs than in ewes; furthermore, in housing when the conditions are wet and warm, straw can become an important risk factor associated with scald.
·         In mild cases, the interdigital skin is covered by a thin layer of white material and is often red as well as swollen. There is no underrunning of the hoof wall or sole and no foul smell.
·         In outbreaks of individual cases, scald can be treated topically using oxytetracycline aerosol spray. In cases with high numbers of incidence, foot baths are more appropriate. 10% ZnSO4 or 3% Formalin solutions are effective control chemicals. Weekly repetition of the footbathing is usually advised throughout the risk period. After bathing, sheep should stand in a dry area to allow the solution to dry onto the feet. Formalin should not be used at concentrations higher than 5% as this can cause severe irritation of the IDS (interdigital skin).

·         Characterised as an extremely painful and emaciating disease.
·         Affected animals are very lame, remain recumbent for long periods and may carry their affected limb. When both forelimbs are affected, sheep walk on their knees.
·         The first sign of footrot is swelling and moistening of the IDS. Following this, a break will occur at the skin horn junction from were infection spreads under the horn tissue so that the wall of the hoof becomes separated and the sole under-run. There is a characteristic foul smelling discharge. In chronic cases, the hoof walls and toes become overgrown, misshapen, trapping dirt and inflammatory exudate between the inflamed, granulating soft tissues of the sole and overgrown horn. Affected feet may also be flystruck.
·         Controlling footrot: there are many ways of controlling and preventing footrot; in practice, footrot control is based on a combination of the following ways… footbathing, foot trimming, antiobiotic injections, vaccination, selection for resistance and eradication. It is important to note the various methods are used for either treatment or prevention. Treating severely affected sheep is usually most appropriately tackled using parenteral antibiotics and hoof trimming; whereas prevention and control is most successful when foot bathing and vaccination is used. Rather than treating individual cases, footrot control is most successful using a whole-flock strategy.

Footrot Treatment Methods
·         Footbathing: best results are seen when the anti-bacterial solutions are applied at the early stages of the disease, when in previously unaffected sheep, infection is limited to the IDS and does not involve the hoof wall. During wet and warm weather (when transmission is high), bathing should be repeated on fortnightly basis. For advanced foot lesions, bathing alone is generally not sufficiently effective.
·         Foot Trimming: Traditionally routine annual foot trimming has been recommended for the control of footrot. However, foot trimming has no role in preventing infection and should not be considered a preventative method. Hoof trimming is only useful to limit the effect of the disease and assist in resolution of the lesion after the infection has under-run the sole and hoof wall in uncontrolled cases of virulent footrot.
Injection of high doses of penicillin: this can be useful for the treatment of advanced cases of virulent footrot where there is sever under-running of hoof horn.

·         Vaccination: can be a useful adjunct for both control and treatment of footrot. Vaccination provides protection against infection for about 4 – 6 months. In some cases a single dose of vaccine administered at the face of an outbreak can reduce the severity of the disease. The net effect of vaccination can be to reduce both the prevalence and severity of the disease. However, whole flock vaccination alone does not eradicate the disease and can prove expensive. In many flocks, vaccination is targeted at specific high-risk groups of animals, such as rams before mating.



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