NEW APPROACHES TO LAMENESS

Transcription

1 Vet Times The website for the veterinary profession NEW APPROACHES TO LAMENESS Author : GRAHAM DUNCANSON Categories : Vets Date : November 24, 2008 GRAHAM DUNCANSON presents an overview of the aetiology and management of lameness in sheep and lambs, as diverse types of ovine ownership emerge THERE are only two certainties in life: death and a lame sheep. Death is a certainty, but I do not believe lameness in sheep needs to happen. Knowing the cause is vital to prevention, but finding the seat of lameness is often difficult. The most common site is the foot, but causes of lameness higher up the leg should not be forgotten, as they are particularly important from a welfare point of view. Although traditional sheep practice is still carried out, there has been a massive increase in new methodologies. New sheep keepers include hobby farmers, rare-breed saviours, those trying to save the planet by not mowing the lawn, and sanctuaries for rescued sheep. Many will expect an approach by the clinician that is similar to small animal practice, so our case management must be more sophisticated. A proper diagnosis needs to be made, and in cases involving a suspected fracture, radiographs will be required. Less dramatic causes of traumatic lameness also need to be considered. Welfare should always be in the clinician s mind. No injectable NSAIDs are currently licensed for the treatment of small ruminants in the UK. However, under the cascade principle, consideration may be given to the use of cattle medications in sheep. 1 / 16

2 These NSAIDs will help to control pain in old pet sheep with non-septic arthritis. However, I find it difficult to justify keeping old lame arthritic sheep in animal sanctuaries on regular pain relief. In my view, it is our duty to counsel these keepers carefully. Foot lameness The bacteria causing foot lameness in sheep can be confusing, and isolation particularly in pure culture is impossible. Bacteroides nodosus may be found in traditional footrot, and the commercially available vaccine is said to contain 10 strains. Treatment with injectable preparations of penicillin and streptomycin combinations seems to be the best advice for old-fashioned footrot. A more severe form is now recognised: contagious ovine digital dermatitis. A Spirochaeta species has been implicated in this disease, and treatment with oxytetracycline seems to be beneficial, particularly with zinc sulphate solution applied topically. Strawberry footrot, a crusty condition of the skin around the pastern, is caused by a Dermatophilus infection. This will cause lameness and if it is linked with contagious viral pustular dermatitis (orf) it is extremely painful. The condition is worsened by grazing in long grass, and it is spread more rapidly if the pasture has thistles or brambles. Scald is a painful condition of the skin between the digits caused by either Fusobacterium necrophorum or Staphylococcus aureus. It is more common in lambs and will appear as outbreaks. Treatment varies depending on the organism involved. F necrophorum is the form that appears most often, so I would start treatment with a three-day course of an injectable penicillin and streptomycin mixture, and topical oxytetracycline spray. If response is poor, a S aureus infection, which is resistant to penicillin, is likely. In this case, I would change to a three-day course of amoxicillin trihydrate and potassium clavulanate. Foot abscesses are normally caused by Arcanobacterium pyogenes. I still use my father s old treatment of poulticing with magnesium sulphate paste on cotton gauze, kept in place with waterproof gutter tape. In his day, animals received an injection of 33 per cent sulphamethazine solution subcutaneously. Nowadays, I would give tilmicosin subcutaneously. This is only licensed for veterinary administration, so if injections were left to the owner, I would choose tylosin sulphate or lincomycin hydrochloride. Chorioptic mange can cause lesions on the lower limbs of sheep, with intense pruritis, in a similar fashion to Psoroptes ovis. 2 / 16

3 The conditions are difficult to differentiate clinically, but the mites can be distinguished microscopically. The psoroptic mites are twice as large as the chorioptic mites. Sarcoptic mites are said to be halfway in size between the two. A trained parasitologist would obviously notice morphological differences. However, as a rule of thumb, if the sheep s body is invested, it is likely to be P ovis, such as sheep scab. If it is just on the lower legs, it is likely to be Chorioptes species, such as foot mange. Other causes of foot lameness The following conditions are rare, but they can cause trouble. Interdigital hyperplasia Rams do get interdigital hyperplasia, but this does not seem to cause lameness unless accompanied by an infection. If this can be controlled, the lameness will normally disappear, avoiding the need for radical surgery. In my experience, surgery for this condition in bulls is worthwhile and usually straightforward. This is not so in rams, which seem even more susceptible to infections after surgery than before. Abscesses Rams seem particularly prone to granulation tissue from a solar abscess. Care must be taken not to remove too much horn tissue when draining these abscesses. If the granulation tissue bubbles out from the hole, the hard horn tissue cannot grow over the top. The granulation tissue then grows more, in a vicious cycle. The granulation tissue, which is vascular but free of nerve endings, needs to be pared back and the whole foot should be bandaged; this should be changed twice weekly for at least two weeks. If the animal is a pet, a red-coloured bandage will help to mask the blood. As a sequel to footrot, whiteline abscesses are common. The under-running infection needs to be exposed, but as much horn as possible should be saved on the wall. Lincomycin hydrochloride injections for five days will help to remove bacterial problems. Topical application of the ubiquitous oxytetracycline spray is useful. Viruses Viruses that cause lameness in sheep can be notifiable. Bluetongue. This disease is uppermost in most farm vets sheep will be stiff or lame, and reluctant to move. They will have a high fever, and the pathognomic foot lesion is a dark red or purple band in the skin, just above the coronet. 3 / 16

4 If clinicians are suspicious, they should stay on the farm and contact DEFRA. Depending on the risk, DEFRA may allow the clinician to leave the premises. Foot-and-mouth disease. You must never leave the farm until told to do so if foot-andmouth is suspected. Sheep will show a transitory fever and lameness. Unlike bluetongue, the coronet is ulcerated. Soil balling was seen during the 2001 foot-and-mouth disease outbreak. Although we did not have the disease in Norfolk, movement was restricted and farmers were forced to keep their sheep on pastures, which became a sea of mud. The soil balling occurred when dry weather arrived. Primary irritant contact dermatitis This disease may catch out the unwary. It can be seen in pet sheep kept in back gardens and on old waste ground. Treatment with bland oily cream is straightforward after the feet have been hosed down. The sheep must be removed from the irritant. Lameness in lambs The causes of foot lameness in adult sheep also affect lambs, particularly if they are older. However, they are rare in very young lambs but this age group has its own problems. Swayback was common when I was a boy, before its aetiology was discovered. By the time I had been to Africa and returned to the UK in 1975, the farmers had the condition under control by treating the ewes with copper between the 10th and 16th week of pregnancy. It is easy to diagnose clinically, as uncoordinated bilateral hindleg movement in an otherwise bright lamb is pathognomic. In my experience, these lambs are born like this and somehow manage to reach up and suck. Delayed swayback has been reported, but I have never seen it. I cannot understand the aetiology surely if the myelin is damaged in the womb, the lamb will be affected at birth? Perhaps the cases are missed at birth. Two other conditions might be confused with swayback: rickets and white muscle disease. Rickets is extremely rare in lambs; I have never seen it in the UK. When I saw the condition in sheep kept in the forests on Mount Kenya, the bent legs were easy to recognise. On the other hand, white muscle disease leaves lambs like rag dolls; they are weak and do not appear bright like swayback lambs. The aetiology is confusing, and I suspect there are actually two forms: selenium deficient and vitamin E deficient. The same commercial injection, containing both 4 / 16

5 selenium and vitamin E, is used for both types. If several cases are seen, I believe it is justifiable to inject each lamb as a preventive measure when the rubber ring is put on the tail. Joint ill is common in young lambs, particularly if they do not receive enough good-quality colostrum. The organism can enter the body through the tonsils, as well as the navel. It is also much more prevalent if the lambing pens are dirty. Treating the navels with iodine or oxytetracycline rarely stops the disease if the ewe s udders are dirty. Older lambs can get septic arthritis from dipping in contaminated solution. Erysipelothrix rhusiopathiae is involved. Tetanus I thought this disease was a thing of the past, as most commercial flocks even organic ones are fully vaccinated against clostridial diseases. However, this is not the case with pet sheep. Although our practice runs smallholder courses and constantly stresses the need for vaccination in our newsletters, many sheep slip through the net. I consider this a welfare issue and I have little patience with negligent owners. The vaccine is very inexpensive and it is possible to supply individual doses for small flocks. Treatment is possible if the disease is caught early enough. A large dose of tetanus antitoxin for example, 6,000IU should be given subcutaneously immediately. Penicillin should be given daily and, although acetyl-promazine is recommended to relax the muscles, I believe that tetanic spasm to this extent warrants euthanasia on welfare grounds. Laminitis I rarely worry about laminitis, as very large numbers of lambs are fed ad-lib creep feed with no ill effects. In addition, ram lambs and shearlings are given large quantities of food to get them ready for sale, to no ill effect. Septic arthritis We have discussed this in lambs, but it also occurs in adults. The most common location, in my experience, is the pedal joint. I would exercise caution before removing the affected claw, as one would with cattle. My experience with sheep is that the whole foot becomes infected, with disastrous results after the operation. With careful pain relief, antibiotics and bandaging, some septic arthritic pedal joints fuse and become pain free. This is a preferable approach compared to surgery. 5 / 16

6 Joint ill is common in young lambs, particularly if they do not receive enough good-quality colostrum. The organism can enter the body through the tonsils, as well as the navel. 6 / 16

7 A well-managed group of sheep. Welfare always needs to be considered in cases of lameness 7 / 16

8 Examples of causes of lameness stemming from the foot: under-run. 8 / 16

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10 Examples of causes of lameness stemming from the foot: footrot. 10 / 16

11 Examples of causes of lameness stemming from the foot: flystrike. 11 / 16

12 An example of a fractured carpus 12 / 16

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14 The author questions the need for topical antibiotics. 14 / 16

15 This lamb was caught in a gate and suffered bilateral carpal fractures. 15 / 16

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