Livestock
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How to tackle scald, footrot and lameness
How to tackle scald, footrot and lameness
MOST outbreaks of lameness in sheep is caused by scald (interdigital dermatitis) or footrot.
Scald and footrot share the same primary cause, the bacterium Fusobacterium necrophorum, which cause damage to the superficial layer of the skin between the claws and enables the establishment of other bacteria, including Dichelobacter nodosus, which causes footrot.
SCALD
Scald is the most common cause of lameness in sheep occurring whenever underfoot conditions are wet. At grass, the incidence is generally greater in lambs than in ewes, but scald can become problematic in housed ewes, where straw bedding becomes wet and warm.
In mild cases, the interdigital skin is red and swollen and covered by a thin layer of white necrotic material. There is no under-running of the hoof wall or sole and no foul smell.
FOOTROT
Pasture around feed troughs and gateways can become trampled, muddy and heavily contaminated with faeces, therefore regular movement of troughs and avoidance of these areas can significantly reduce the incidence of foot diseases.
Individual cases of scald can be treated using oxytetracycline aerosol sprays. When several animals are affected, walking sheep through a 10% zinc sulphate or 3% formalin footbath is usually effective.
It is usually necessary to repeat the footbathing at weekly intervals throughout the risk period and after foot bathing sheep must stand in a dry area.
LAMENESS
Footrot is an extremely painful disease for sheep of all ages. Affected animals can lose weight rapidly and have reduced wool quality and yield.
Lameness affecting rams during the breeding season can result in failure to serve ewes.
The severity of footrot depends partly on the strain of D. nodosus present. Mild D. nodosus strains result only in separation of the hoof horn at the heels and back of the sole (benign footrot), while virulent strains can result in complete separation of the horn of the hoof wall and sole.
SIGNS
The first sign of footrot is swelling and moistening of the interdigital skin. A break occurs at the skin horn junction from where infection spreads under the horn tissue so that the wall of the hoof becomes separated and the sole under-run. There is a characteristic unpleasant smelling discharge. In long-standing cases, the hoof walls and toes become overgrown and misshapen. Animals with virulent footrot are extremely lame, remain recumbent for long periods and may carry the affected leg.
When both forelimbs are affected, animals may walk on their knees. Severely affected feet often become flystruck.
CONTROL
Various methods can be used to control footrot, including: foot bathing, foot trimming, antibiotic injections, vaccination, selection for resistance and eradication.
In practice, footrot control is based on a combination of the above. It is important to distinguish between those methods which are useful for treating severely affected sheep, such as trimming and parenteral antibiotics and those which will help control disease when used correctly, such as foot bathing and vaccination.
Foot bathing: Application of antibacterial solutions in a foot bath is most effective for the control of footrot when practiced during the early
stages of the disease, when infection in previously unaffected sheep is limited to the interdigital skin and does not involve the hoof wall. It usually needs to be repeated at fortnightly intervals during warm and wet weather. Foot bathing alone is not particularly effective for the treatment of advanced footrot lesions.
Foot trimming: Though traditionally routine annual
foot trimming is recommended for the control of footrot, it
has no role in preventing infection. Hoof trimming is
only useful to limit the effect
of the disease and assist in the resolution of the lesion after
the infection has under-run
the sole and hoof wall.
Antibiotic injections: Injection of high doses of penicillin can be useful for the treatment of advanced cases of virulent footrot.
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 during an outbreak can reduce the severity. Whole flock vaccination alone does not eradicate footrot and can
prove expensive. In many
flocks, vaccination is targeted
at specific high-risk groups
of animals, such as rams
before mating.
NADIS is sponsored by EBLEX, Merial Animal Health, Pfizer Animal Health
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