Routine foot care and dealing with flock problems are more likely to be successfully performed if good handling facilities and correct equipment are available. Several systems which incorporate devices to turn the sheep over are available, so that work can be carried out in the normal standing position reducing back strain; these are well worth investigating particularly for larger flocks. An adequate footbath should be available, preferably one large enough to stand a number of sheep in, rather than the narrow 'run through' type. A special mat can be placed in the bath to reduce the volume of chemical necessary to ensure proper coverage of all feet. A dry area where the sheep can stand for a while after passing through the chemical will ensure that efforts are not wasted by turning sheep out immediately into wet grass.

A good quality pair of precision foot shears and a sharp knife are required. These should be disinfected after paring infected feet, and at the end of each session. They should be cleaned and oiled, not left to rust!

Paring Feet

This should be carried out with care, particularly avoiding over-paring which causes bleeding. This is unnecessarily painful and may cause permanent damage to the foot. Where loose horn is present, it should be carefully pared back, but if an animal is badly affected with foot rot, treatment with injectable antibiotic (after discussion with the vet) may be the most useful first line of attack. Paring can then be done a few days later when healing has commenced.

Precautions On Introducing New Sheep Into The Flock

Foot rot (or a new strain of it) can easily be inadvertently introduced into a flock with the purchase of new sheep (don't forget the rams as well as the ewes). These should never be added to the resident flock without a period of quarantine, during which time the feet should be examined and appropriate treatment carried out where necessary. Even if all appears well, it is good practice to footbath as a precaution.

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Although scald and foot rot are the most common types of lameness, there are other causes. It is important to make sure that the diagnosis is correct before deciding on treatment. This may sound simple, but confusion can arise and can be the explanation if well-recognised treatments for foot rot seem not to have the desired effect.

Scald

Scald affects the skin between the claws only. Instead of being dry, the skin is moist and painful (in fact the degree of lameness often seems out of all proportion to the appearance of the affected foot). Scald is not invasive and there is no separation of the horn from deeper tissues (see Figure 1 below). It is caused by the environmental bacterium Fusobacterium necrophorum, thus any sheep can be affected. It is particularly common in warm, wet weather if the grass is not kept grazed short.

image of interdigital lesion

Foot Rot

This condition starts as scald, but progresses when a second species of bacterium, Dichelobacter nodosus (which is found only in infected feet and can live on pasture for only 2-3 weeks), takes advantage of the damage already done to the skin between the claws to invade the hoof, leading to separation of the horn from the underlying sensitive tissues of the foot. The separation starts in the heel area and, depending on the strain of bacterium involved, may spread across the sole and eventually up the wall of the hoof (see Figure 2 opposite). One or both claws of one or more feet may be affected; it can be recognised by the part of the hoof affected and by the build up of characteristic smelly, grey debris under the loosened horn. Foot rot spreads most readily in warm, moist weather outdoors and when sheep are housed.

New Virulent Foot Rot

Recently, an apparently new type of very aggressive foot rot has been seen in a number of flocks. This causes severe inflammation of the foot, usually (but not always) affecting both claws, the cleft and often the skin above the hoof of one or more feet. The horn becomes undermined and may become completely detached. Unlike 'normal' foot rot, where horn will usually re-grow if the foot is treated, neglected cases of this new type may sustain permanent damage to the coronary band where new horn is produced, so healing does not take place and the animal may have to be slaughtered on welfare grounds.

image of interdigital lesion

Problems Affecting The White Line

The white line is the site at which the horn of the wall of the hoof joins that of the sole (a careful look at a newly pared foot will reveal it running around the outer edge of the sole, and will show why it is called the white line). It is a naturally weak area in the horn and there are two different problems which can occur here, both eventually leading to lameness.
The first, toe abscess, occurs when infection develops at a point somewhere along the white line, pus forms under the wall of the hoof and the animal becomes acutely lame (see Figure 3 below). The affected claw can be identified by pain response when it is manipulated. Careful paring of the sole will usually reveal a dark mark at some point along the white line; sometimes pus will be released during paring. If not treated, the pus eventually bursts out at the coronary band and the animal gradually recovers. Some animals suffer from repeated attacks, probably because of a permanent defect in the horn at that point.

image of interdigital lesion

The second problem, shelly hoof, is a more extensive degeneration of the white line. The hoof wall becomes separated and forms a pocket which becomes impacted with dirt and other debris (see Figure 4). In the early stages, the sheep is not lame, and it is very common to find mildly affected animals at routine foot paring sessions.

If the loose horn is not pared away, some cases progress to the stage where a large semicircular area of the horn of the hoof wall is detached, impacted debris is forced into deeper tissues, pus forms and the sheep becomes lame. As occurs with a toe abscess, the pus eventually bursts at the coronary band and recovery gradually follows.

image of interdigital lesion

Foot Abscess

This is a more serious condition, where the deeper parts of the hoof, including the pedal joint, become infected. The animal (often a heavy ram or ewe) is acutely lame, the affected claw is swollen and very painful. Within a short time pus bursts out at several sites around the coronary band, including between the claws. The deeper structures of the foot are usually permanently damaged, the claw becomes chronically swollen and misshapen and the animal remains permanently lame. In the case of a ram, his ability to do his work is obviously greatly impaired.

image of interdigital lesion

Granuloma

This is a strawberry-shaped piece of proud flesh which grows at a site where the foot has been damaged and the overlying horn is unable to grow back normally. The most common site is at the toe and, in many cases, its development follows over-paring which has caused bleeding. They can also occur for other reasons, for example following a penetrating injury. The usual picture is of an animal which has an overgrown misshapen hoof, because it is chronically lame and doesn't put its full weight on the foot; when loose horn is pared away, the proud flesh is exposed and this bleeds as soon as it is touched. If it is cut off, profuse bleeding occurs at first, then it gradually re-grows and it again becomes partially concealed by loose, overgrown horn.

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Scald is a difficult and frustrating condition to tackle, as the causal organism is widely found in the environment so cannot be eliminated. If small numbers of sheep, or, more likely, lambs are affected, the commonly used coloured antibiotic spray is effective, providing the treated animals are not immediately turned back on to wet grass. For larger numbers, or for flocks with recurring problems, the only practical answer at present is regular (perhaps onceweekly) foot bathing. Any of the commonly used chemicals such as zinc sulphate, formalin or other proprietary product should be effective. Because the infection is a superficial one, it is not necessary to stand animals in the bath for very long; in fact, one of the most practical and cheap methods is to walk them slowly through a weak solution of formalin (2-3% only). At this dilution it is usually effective without the hazard of over-hardening the hooves and is not as unpleasant as stronger solutions. Other measures to reduce the risk include keeping grass grazed short, and making sure gateways, feed and water trough surrounds etc. are kept free of mud.

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Foot rot should always be treated as an infectious disease and needs to be tackled on a flock basis. It is a waste of effort only to treat obviously lame sheep, since there will be many milder cases which will continue to act as a source of infection for others. It is possible to eradicate foot rot, as has been done in parts of Australia and in some flocks in the UK. This is really only practicable in closed flocks, and, if achieved, rigorous measures have to be taken to maintain the foot rot free status by making sure neighbours' sheep do not stray in and paying careful attention to any introductions such as rams.

For most flocks, control rather than eradication has to be the goal. There is no easy way, but a combination of measures such as regular inspection of feet, regular foot bathing, treatment of severe cases with injectable antibiotics and vaccination are likely to be necessary. All sheep should go through the foot bath, and the treatment most commonly used is zinc sulphate solution. The disadvantage of this product is that infected sheep need to stand in the bath for some time (15-30 minutes depending on the particular preparation). Many farmers think it just is not possible to do this for a large flock, but it can be done if sheep are sorted into infected and uninfected groups as feet are trimmed, then foot bathed separately, with more time given to the infected groups. Having divided off the infected animals, they should be kept separate so that treatment can be repeated until cured. If possible, animals should be put back on to fields which have been clear of sheep for about 3 weeks.

Vaccination can be very useful in reducing the number of infected sheep, since it can be curative as well as preventive. The drawbacks are cost and the possibility of vaccination reactions to the oily base. Great care needs to be taken when vaccinating, as it can cause severe reactions if accidentally injected into people.

The final key to controlling foot rot is to cull persistently affected animals which do not fully respond to treatment, since these act as a continuous source of infection for the rest of the flock.

Too little is known about the 'new' virulent form of foot rot to be able to give comprehensive advice, but indications are that foot bathing with zinc sulphate (10%) at weekly intervals, or injecting with long-acting oxytetracycline are both successful, providing treatment is done before permanent damage occurs to the foot.

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Individual sheep which are lame as a result of pus developing under the wall of the hoof (toe abscess and shelly hoof) can often be helped by a little careful paring along the white line, with loose horn being carefully removed. With luck, this will release the pus, or at least allow it to find its own way out faster. The horn should not be pared so deeply that bleeding is caused. In difficult cases, poulticing the foot for a couple of days will soften the horn and speed recovery. Further paring to remove underrun horn may be necessary as the hoof heals, but should always be done carefully and not excessively.

Foot abscess (infection of the pedal joint) is a much more serious condition. The animal is severely lame and, because the infection is deep in the foot and involves the joint, it is unlikely to recover for many weeks, if at all. Veterinary attention is needed, the most usual treatment being amputation of affected claw. This quickly relieves the pain and it usually heals well, giving the possibility of another season or two of productive life for the animal.

Veterinary attention is also necessary to treat granulomas. It is necessary to anaesthetise the foot before trimming to expose the granuloma, which is removed, then the base cauterised. If done correctly, the foot can be restored to near normal in most cases. The important message, though, is not to cause them in the first place!

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There are many other reasons why sheep become lame. These may involve the foot, joints, bones, nerves or muscles of the legs. This news sheet has described the most common causes of lameness in adult sheep. If lame sheep are not responding to treatment or if many are lame, veterinary help should be sought.

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