14 Lameness

Lame sheep are such a common problem that this topic deserves a chapter to itself. Lameness is a welfare and economic issue – lame sheep are suffering pain, and will be less productive as a result. There are many causes of lameness, some of which have well recognized methods of treatment and control, but however good foot care is in a particular flock, there may be a few sheep that go lame in spite of everything. We know, we have experienced this! The important thing is to recognize lameness cases at an early stage – walking with a nod of the head is an early sign – rather than waiting until animals are grazing on their knees, or obviously standing on three legs. Then treat them as soon as is practically possible.

The following are the key issues:

Sheep that become lame should be examined as soon as is reasonably possible.
The cause of lameness should be correctly identified.
Appropriate treatment should be given.
Veterinary help should be sought if the cause is not clear or the treatment is not working.
If the cause is an infectious agent, a suitable control programme should be put in place.

Fig. 528 Why is this sheep lame, and how long has she been lame?

Fig. 529 Two severely lame sheep, which, judging from the appearance of the foot of one of them, have been lame for a considerable time. It is not acceptable to leave chronically lame sheep untreated.

Fig. 530 This sheep has serious damage to the knee joint as a result of prolonged lameness, causing her to kneel to eat. Encrusted manure on the knees also shows when a sheep has been kneeling as a result of chronic lameness.

Fig. 531 Both feet of this ram are grossly overgrown and would benefit from careful trimming.

Fig. 532 A typical granuloma visible at the toe.

The vast majority of lameness in adult sheep originates in the foot. In younger animals joint infections are the commonest cause, and these have already been dealt with in Chapters 11 and 12.

Causes of Lameness in the Foot

Overgrowth of Horn

Overgrown horn does not cause lameness in itself, but the excess horn can crack or trap pieces of grit underneath, both of which circumstances can lead to lameness. We have already discussed trimming feet in Chapter 2 and have drawn attention to the fact that many feet are trimmed unnecessarily and too hard. Only trim, carefully, excessively overgrown horn, and do not cut too deeply causing bleeding.

Toe Granuloma

Toe granulomas are sometimes referred to as ‘strawberry toe’, since the most common site for one to develop is at the toe. A granuloma is a piece of granulation tissue (proud flesh) that develops when the foot is injured, most commonly as a result of overtrimming; it can also develop following a penetrating wound such as caused by a thorn, and also sometimes in chronic footrot cases.

Granulomas are difficult to deal with as they bleed profusely and regrow if they are simply cut off. One solution that sometimes works if the granuloma has a narrow enough base is to put on a rubber castration ring – this cuts off the blood supply. Another method is to carefully apply copper sulphate crystals and then bandage the foot, but the foot needs checking frequently to make sure the granuloma is drying up. The alternative is to seek veterinary help.

Soil Balling

Soil balling occurs when mud and grass or manure becomes impacted in the interdigital space. It leads to lameness as a result of the discomfort it causes, and because the interdigital skin becomes rubbed and infected. Diagnosis and treatment are obvious, though it is difficult to know how to prevent it happening in the first place.

Interdigital Hyperplasia

Interdigital hyperplasia is where a fold of skin grows in the interdigital space (sometimes there are two present, as they grow from the skin/horn junction, so one can grow from each side). These gradually get bigger as the sheep gets older. If these cause problems, the only possible treatment is surgical removal by your vet.

Fig. 533 The hard lump of soil and grass between the claws causes discomfort and lameness.

Interdigital Dermatitis

Interdigital dermatitis, or scald, is an infection of the skin of the interdigital space by a common bacterium, Fusobacterium necrophorum, widely present in the environment. It occurs when the skin in the cleft of the foot is subject to prolonged wetting or other damage, such as caused by long mature grass or stubble. Instead of looking healthy and dry, the skin looks damp and inflamed or greyish in colour. It is particularly common in growing lambs, but can occur in older sheep too, especially when housed, and causes sudden lameness, often in several animals at the same time. It can progress to footrot if the specific cause of that is present in the flock (see below). Treatment is by spraying with antibiotic or footbathing (see panel, pages 178–9).

Footrot

This very common disease starts as interdigital dermatitis, but progresses into a deeper infection as the result of invasion of the horn with a second bacterium, Dichelobacter nodosus, the specific cause of footrot. These bacteria cannot survive off sheep’s feet for more than seven to ten days, so the main source of infection for other animals is diseased feet contaminating the environment. Infection spreads in warm, damp weather and does not spread in very cold (less than 10°C), or hot, dry conditions. The distinguishing feature from interdigital dermatitis is that in footrot the horn of the sole becomes underrun and separated from the underlying sensitive tissues. The separation starts towards the back of the cleft, near the heel, and careful examination is necessary to see that this is happening in the early stages.

Fig. 534 A particularly large interdigital growth that needs surgical removal if the sheep is not to have repeated spells of lameness.

Fig. 535 A typical case of interdigital dermatitis, with the skin between the claws looking rather swollen, greyish and damp. This is the precursor to footrot.

Fig. 536 An early case of footrot – separation of the sole has started, and can be seen as a dark line near the heel where the fingers are pulling the horn away from the interdigital skin in the claw on the left.

The Treatment and Control of Footrot

In small, self-contained flocks it should be possible to reduce or even eliminate footrot from the flock, providing that stray sheep cannot gain access and that any sheep brought in, such as the occasional ram, are carefully checked and quarantined before mixing with the resident flock. Getting and keeping control in larger flocks is a much harder task, but the benefits of controlling the disease, both in terms of welfare and production, are well worth all the hard work involved. Infected animals need treating, whatever the time of year, but making a concerted effort to tackle the whole flock is best done in the summer between weaning and tupping time when there are fewest sheep on the farm and there is a chance of drier weather.

Here is a summary of the most important points in controlling this disease – the main points to note are the use of injectable antibiotic for treatment, and not to trim the feet immediately:

In a large or heavily infected flock, consider the use of vaccination (see Chapter 4).
Examine all feet carefully and treat all infected sheep with an injection of antibiotic – you will need to consult your vet about this.
Do not trim the feet of infected sheep immediately, other than sufficiently to diagnose – leave trimming until treatment has had time to work (at least five days).
Keep these sheep separate if possible.
Put sheep judged to be uninfected through a 10 per cent zinc sulphate foot bath allowing the correct stand-in time, in case these have an early infection that has been missed.
Put these sheep on pasture that has not had sheep on it for two weeks or more.
Keep a careful eye on them, footbath once or twice more, and examine, remove and treat any that go lame as soon as possible.
Re-examine treated sheep after five to seven days; trim minimally – only obviously loose horn.
Re-treat with antibiotic any that still have an obvious infection, and footbath all.
Only put treated sheep back with the rest of the flock when you are sure they are cured, footbathing them before mixing.
Be prepared to cull any sheep that do not respond to treatment, or have chronically misshapen feet – these will be a constant risk to the rest if they are kept.
Do not let the number of lame sheep get out of control again – early examination and treatment saves undoing all the hard work that has already been done.

Fig. 537 In this foot the claw on the right has the typical appearance of footrot, with underrunning and separation of the sole visible.

Fig. 538 In this foot from a slaughterhouse both claws are affected with footrot. The extent of the underrunning has been exposed by careful trimming.

Fig. 539 Another advanced case of footrot. The claw on the left has some granulation tissue near the toe, probably a result of the chronic footrot infection.

Fig. 540 Consult your vet about using injectable antibiotics for treating footrot. An antibiotic aerosol spray is effective for treating interdigital dermatitis and as an adjunct to the treatment of footrot with injectable antibiotics, but is not sufficient for treating severe footrot.

FOOTBATHING

This is the easiest way of treating a large number of sheep’s feet, but has to be done correctly or it is a complete waste of time, or could even make matters worse. The handling and standing area around the footbath must be kept reasonably clean, with good access back to the field, or all the hard work done could be wasted. Incorporating a plain water bath before the treatment bath helps clean feet in preparation for treatment, and having a dry standing area for sheep for up to one hour after treatment is crucial. Decide how the footbath solution can be disposed of safely after use. The following products are most commonly used:

Zinc sulphate 10 per cent solution – this is effective and kind to the feet, but the sheep do need to stand in it for two to fifteen minutes, depending on the particular product used. It does not ‘go off’ even when it looks dirty.

Formalin 2–3 per cent solution – this is cheap but irritant and unpleasant to use. It is effective if sheep are just walked through slowly. It may be the most practical way of controlling interdigital dermatitis in large groups of growing lambs. It does lose its efficacy when it becomes very contaminated.

Copper sulphate – as this is poisonous for sheep, its use is not recommended.

Various proprietary compounds – if you choose to use one of these, make sure there is good data showing its efficacy and follow the instructions

Fig. 541 Walking sheep down a muddy track like this after footbathing means the treatment will have been a complete waste of time.

Fig. 542 Zinc sulphate is effective and non-irritant, but sheep do need to stand in it in order for it to work properly. Adding some detergent reduces the necessary stand-in time.

Fig. 543 Formalin solution is very unpleasant to use, and must never be used at more than 3 per cent strength. Stronger solutions can overharden and damage horn.

Fig. 544 These handling pens have a concrete floor that can be easily cleaned.

Fig. 545 The floor of this pen is covered in faeces and mud and clearly has not been cleaned for some time.

Fig. 546 This is a suitable footbath for standing a group of sheep in zinc sulphate solution, with a dry concrete area for them to stand on outside.

Fig. 547 A large footbath for a big flock. It has two sections, the first containing water to wash the feet, the second containing the treatment solution.

Fig. 548 Footbaths should be cleaned out regularly – this one is very dirty.

Contagious Ovine Digital Dermatitis (CODD)

This serious foot disease is relatively new and only seems to be a problem in this country. It was given its name because it seems likely that it is caused by the same bacteria that cause digital dermatitis, a common cause of lameness in dairy cattle. Unlike footrot, where the first signs are seen in the cleft of the foot, spreading from here across the sole to the heel, the first signs of this disease are seen at the coronary band. There is inflammation and often haemorrhage here, with separation of the horn which extends rapidly down the claw. This results in most of the horn of the hoof becoming loose, leaving haemorrhagic-looking underlying sensitive tissue exposed. Affected animals are extremely lame as a result. We do not know much about the disease, but experience shows that it can spread quickly, particularly in housed sheep. There may be some immunity after infection, but little is known about this.

Treatment is not straightforward, as those products used for footrot often do not work for this disease; you will need to consult your vet about what is best to use. An antibiotic footbath is commonly advocated, but this is expensive. Injecting with antibiotic is an alternative. Some animals have been successfully treated by applying antibiotic from a spray bottle, but this needs repeating at least twice more, so is labour-intensive. If affected animals are not treated, damage to the foot can become chronic, with permanently damaged feet being the end result. The most important thing about this disease is, if you haven’t got it, don’t risk getting it by accidentally buying it in.

Fig. 549 The typical appearance of a hoof affected with CODD, where the horn has become detached from the coronary band downwards, leaving the sensitive part of the foot exposed.

Fig. 550 Removal of the loose horn shows the extent of the damage.

Fig. 551 On this foot, both claws are affected. The haemorrhagic appearance is clearly visible.

Fig. 552 An untreated chronic case of CODD. Loss of hair around the top of the foot shows that inflammation has been present and both claws show chronic changes. This foot is unlikely to recover to normal.

Fig. 553 Treating sheep by spraying with antibiotic solution (from your vet). This needs repeating several times. Alternatively use a footbath containing antibiotic to treat larger numbers of animals.

Fig. 554 This healthy foot shows clearly where the horn of the wall and sole join. The wall horn wraps very slightly over the sole and there is no separation between the wall and sole.

White Line Disease (Shelly Hoof)

The white line is a narrow zone at the junction of the wall horn and sole horn of the hoof. As the name suggests, the horn at this point is white in colour and it is rather softer than the rest of the horn, making it more prone to damage. Separation of varying extent along this line is an extremely common problem of sheep’s feet, and is often confused with footrot. The characteristic appearance is of a pocket forming at the junction of the wall of the hoof and the sole.

Many sheep have hooves affected by this but are not lame, but the potential is there for mud or grit to get into the pocket and to be driven deeper under the wall until an abscess forms, when the sheep becomes acutely lame. If untreated, the pus works its way up to the coronary band where it bursts out and the sheep gradually recovers, but a crack forms in the hoof wall at this point. There is no known method of prevention. The loosened horn in affected claws should be carefully pared away until the pocket is no longer present.

Fig. 555 A claw with minor separation along the white line showing the typical appearance after paring. The horn is dry and uninfected.

Fig. 556 A more advanced case after paring.

Fig. 557 An advanced case after paring. The underlying structures, the laminae that produce the horn, look dirty and damp indicating that some infection is present. If this foot had been left, it is likely that pus would have formed under the wall, making the sheep very lame.

Fig. 558 A very large separation, showing how easy it would be for a piece of grit or small stone to become impacted in it.

Fig. 559 The left claw has a black mark in the white line showing where the origin of a white line abscess could be.

Toe Abscess (White Line Abscess)

This is a variation of white line disease where the defect is more discrete than in shelly hoof. Rather than an obvious pocket forming, a black mark is visible in the white line showing where the defect is, and which leads to where pus has formed. Although the name suggests these usually occur at the toe, this is not always the case, and it can occur anywhere along the white line.

Usually the first sign is that the sheep is acutely lame, with heat and pain in the affected claw. After a few days, pus bursts out at the coronary band and the sheep gradually recovers. A crack may form in the hoof wall and this gradually moves down the hoof as it grows. It may be best to leave these cases for the pus to burst out on its own, rather than paring too deeply and causing more damage. The application of a poultice can speed things up.

Pedal Joint Abscess

This is a sporadic but serious cause of lameness, often affecting heavy rams although ewes can be affected as well. Lameness is sudden and severe, and the affected claw is hot, painful and swollen. It is this swelling that differentiates it from the toe abscess described above. In toe abscesses the pus forms under the wall of the hoof, and once released, the foot usually heals and returns to normal. In pedal joint abscess, the pus forms within the joint deep within the foot, disrupting the joint and causing damage to the bone in the foot. Within a day or two, pus bursts out, first in the cleft of the foot, then at other points around the coronary band, but the swelling and lameness persist.

If these cases are spotted in the first few days, they may be successfully treated by your vet, but if they are left for some time, the damage becomes untreatable and the animal will be permanently lame with a deformed foot. At this stage the only treatment may be amputation of the affected claw.

Fig. 560 A toe abscess that has burst at the coronary band in the upper claw.

Fig. 561 This foot has had a white line abscess. The crack shows where pus burst out when this part of the horn was at the coronary band, and is now moving down the foot as the horn carries on growing.

Fig. 562 Another white line abscess that occurred some weeks previously. A horizontal crack is visible at the top of the pared-out track, showing where the pus burst out. Normal horn is growing above this.

Fig. 563 A healed white line abscess. The overlying horn has been pared away to show the extent of the area where pus spread in the acute stage.

Fig. 564 An acute pedal joint abscess. Pus has burst out in the interdigital space and the foot is swollen above the claw.

Other Causes of Lameness

Joint infections occur occasionally in individual adult sheep but are not common on a flock basis. Fractures of the legs also occur occasionally. If these are below the knee or hock, it is usually possible for your vet to treat them by applying a splint or plaster cast. If bones higher up the limb are affected, slaughter is usually the only option.

Fig. 565 Veterinary treatment of an acute pedal joint abscess, by inserting a tube into the joint and flushing with sterile fluid. The ram made a full recovery.

Fig. 566 A chronic pedal joint abscess with swelling all round the coronary band and discharging sinuses. It is not possible to return this foot to normal, and amputation of the claw may be the only solution.

Fig. 567 This foot shows gross distortion as a result of a pedal joint abscess that occurred some months previously. The affected claw was amputated, allowing the sheep to walk normally again.

Fig. 568 Fractures of the lower legs can usually be successfully treated.

Fig. 569 The typical appearance of ‘strawberry footrot’, which is nothing to do with either footrot or ‘strawberry toe’.

Fig. 570 An elbow joint badly affected with arthritic changes (above), compared with a more normal joint from the same animal (below). It is not difficult to imagine how painful this condition would be, and shows that treatment is hopeless.