This chapter covers notifiable diseases, and other diseases that do not occur either in a particular age group or at a specific time in the annual production cycle. It is not practicable to cover every possible disease that may occur, particularly rare ones, but we have tried to pick out the most important ones.

Notifiable Diseases

These are diseases that, by law, you must report to the local Animal Health Office if you suspect them. Details are on the Defra web site www.defra.gov.uk. If you do not know who to contact, your vet will be able to tell you.

Foot and Mouth Disease (FMD)

After the epidemic of 2001 and the escape of virus in 2007, everyone hopes such disasters will never occur again. Movement regulations have been tightened up considerably to reduce the risk of the massive spread that occurred in 2001, so if these sometimes seem restrictive, it is for the good of the national flock.

In sheep, the signs vary from mild lameness and lethargy, to more obvious illness in pregnant ewes or sudden death in newborn lambs. The most characteristic signs are blisters in the mouth and around the top of the hooves, but these may not be very obvious. Remember that sheep often get traumatic ulcers on their gums, particularly in the centre below the teeth in the lower jaw, but these are abrasions caused by rough grazing and should not be confused with FMD.

Bluetongue (BT)

This viral disease is spread by midges, and there is always a risk of disease-carrying midges being blown across the English Channel from northern Europe during the summer months. Signs of infection are swelling of the head, especially the lips and tongue, a high temperature, nasal discharge and lameness. (See Chapter 4 for details on vaccination.)

Tuberculosis (TB)

Sheep have generally been considered to be fairly resistant to TB, but with the widespread problems of TB in cattle and the link to badgers, more sheep are likely to be exposed to infection. During the writing of this book an outbreak in sheep was reported, showing as chronic weight loss with internal abscesses similar to those found in CLA (see Chapter 6).

Scrapie

This neurological disease, which has been known for centuries, has been very topical in recent years mainly because of its being very similar to BSE in cattle and vCJD in people, and its control has been politically driven because of public health concerns; however, these now seem unlikely. The susceptibility of sheep to the classical disease depends on their genetic make-up, and this has been used as the basis for a control plan, the National Scrapie Plan (NSP), to reduce the number of susceptible sheep in the national flock. Most of the NSP schemes have been wound down, but in flocks in which classical scrapie is diagnosed, it is mandatory either to slaughter the flock or to genotype them and remove the susceptible ones.

Fig. 571 Most notifiable diseases have implications for the health and future of whole flocks.

In recent years, a different type of scrapie called atypical scrapie has been diagnosed in a small number of sheep. This is not thought to be of any danger to the rest of the flock, so the same control measures are not applied.

Suspected cases of either type must be notified. It mainly affects sheep over about two years of age, and the clinical signs can be any combination of intense itching, an unsteady gait, behavioural changes and weight loss.

 

There are various other rare and exotic diseases, the possibility of which should never be forgotten. If in doubt over sheep which are becoming ill, behaving oddly, or dying for no apparent explanation, always seek veterinary advice.

Other Diseases and Problems

Skin and Wool Problems

The most important diseases in this category are undoubtedly those caused by external parasites, already covered in Chapter 7. Any flock problem involving sheep being itchy and losing their wool should be viewed as being likely to be due to parasites, and should be investigated to find the cause before choosing an appropriate treatment. There are many other diseases that lead to scabbing of the skin or wool loss.

Fig. 573 This sheep has woolbreak as the result of a previous illness. Normal fleece will regrow.

Wool Loss

Natural shedding: Some breeds and some individuals naturally shed part or all of their fleeces in spring. This is a throwback to what happens in primitive sheep and is of no concern, apart from loss of the value of the fleece (very little!), and the mess it creates in the field.

Woolbreak: This often occurs after sheep have been under some form of stress, such as food shortage, pregnancy toxaemia, a difficult lambing or mastitis. The growth of wool is affected, leading to thinning of the fibres, which become weak and break, leading to partial loss of the fleece. The skin is normal, and once the sheep recovers, normal wool growth starts again.

Skin Infections

Orf: We have already encountered this viral disease as a cause of teat lesions in ewes, mouth and lip lesions in lambs, and as part of the cause of strawberry footrot. This virus can affect any age group of lambs or sheep, and most often appears as characteristic scabs around the mouth; however, sometimes it can cause proliferative lesions at other sites on the face, ears or legs. Most sheep recover, but occasionally there are individuals that do not seem able to mount an immune response, and the lesion persists. See Chapter 4 on vaccination, and remember that this virus can infect people, so wear protective gloves when handling infected sheep or the vaccine.

Staphylococcal dermatitis: Bacteria called staphylococci that live on the skin can cause small papules of no significance; however, some pathogenic strains can cause more serious skin disease, where deep bleeding ulcers occur. These usually have a zone of hair loss surrounding the scabbed area. They are most commonwhere there is a shortage of trough space, and sheep bang their heads and legs as they push to get food. They can be treated with antibiotics, but may leave behind a hairless, scarred area. These are the same bacteria that can cause serious teat lesions in lactating ewes (see Chapter 12).

Dermatophilus infection (mycotic dermatitis, lumpy wool): This is a bacterial disease that can cause anything from mild scabs on the nose or ears, through to severe exudation and scabbing of the skin along the whole of the back. It is most common in the wetter conditions of the western parts of the country, particularly in sheep whose fleeces tend to gather water, rather than longer fleeces where the water runs off. When the woolled areas are affected, the scabs that form on the skin surface dry out and grow out with the fleece as the wool grows, causing it to become matted and spoiled. Treatment is usually only needed in severe cases. Injectable antibiotics are effective, or a wash of zinc sulphate solution can be used. It is best to remove the wool from the affected area first.

Ringworm: Although a more common problem in cattle, there seem to have been an increasing number of cases in sheep recently. The ringworm lesions are usually seen as scabby areas on the head or ears, but they are occasionally seen on the body if newly shorn sheep become infected. Remember that this disease is infectious to people. There is no licensed treatment available, although antiseptics such as iodine may be helpful.

Photosensitization: This occurs in two ways: either by the sheep eating specific plants that contain chemicals, which get into the bloodstream and sensitize the skin to light; or as a result of impaired liver function, which allows a breakdown product of chlorophyll (in grass) to get into the general circulation. In either case, the sheep looks miserable, and the unpigmented parts of the skin, particularly the head and ears, swell up, exude serum and eventually dry up and crack. Commonly, the tips of the ears are lost. Most animals recover if they are housed or can find shade, although if the origin is liver disease this may well adversely affect chances of recovery.

Midge hypersensitivity: This sporadic problem seems to affect particular flocks of sheep, particularly those with dark-coloured bellies. It is almost certainly the sheep equivalent of sweet itch in horses and starts in late spring, lasting through to the first frosts of autumn. Affected sheep show great irritation with the head, ears, legs, udder and perineal skin being affected; this becomes thickened and damaged as a result of the sheep constantly rubbing. The seasonal occurrence is diagnostic.

The severity of the attack can be reduced by applying a synthetic pyrethroid (SP) pour-on before the midge season starts, repeating as necessary during the summer, together with better management of overgrown vegetation to reduce the midge habitat.

Neurological Problems

Neurological diseases are common, and can affect individual animals or several of a group. Diagnosis can be difficult, but the age of the affected animal(s), the sex, and the stage of the production cycle can all help narrow down the possibilities. We have already covered scrapie, the common problems of ewes around lambing, as well as some affecting rams and lambs of various ages. Other possibilities are described below.

Gid

Affected sheep (usually less than two years old) commonly show the following symptoms: they turn in circles, are blind in one eye, and become increasingly dull. Gid is the result of a tapeworm cyst, picked up from infected dog faeces, which forms in the brain, often growing to a considerable size. The site of the cyst determines the clinical picture, so sometimes different neurological signs are present.

Some cysts can be surgically removed successfully, though this may not be financially worthwhile; however, some vets like the challenge of brain surgery! Regular dosing of dogs with an effective tapeworm treatment, and proper disposal of carcases, reduces the likelihood of this disease occurring.

Cerebrocortical Necrosis (CCN)

CCN is most common in growing lambs, but can also be seen sporadically in adults, and is the result of thiamine (vitamin B1) deficiency. This may be precipitated by a change in diet. The characteristic signs are ‘star gazing’, where the head is thrown back with the nose pointing upwards, blindness, with the eyes rolled upwards, and stiffness of the legs. Treatment with vitamin B1 is usually successful if given in the early stages, but permanent brain damage occurs in the later stages.

Middle Ear Infection

This infection is another sporadic disease that can cause an altered head and leg position, and one-sided paralysis of the facial muscles leading to a drooping ear, eyelid and muzzle. The head is usually tilted to one side, and the animal may walk in circles or fall over. It can be confused with listeriosis (see Chapter 10). Treatment with antibiotics may be successful if given promptly.

Texel and Beltex Wobblers

Wobbler syndrome is a problem recently identified as the result of pressure on the spinal cord in the lower neck region by a pad of fat that protrudes into the spinal canal. Affected animals have, as the name suggests, a wobbly or swaying gait. There is no cure, and there may be a genetic predisposition, so offspring of affected animals should not be kept for breeding.

Eye Problems

Entropion (Inturned Eyelids)

A big problem in some flocks, this has already been covered in Chapter 11. This condition should always be suspected if young lambs develop runny eyes and the cornea becomes cloudy-looking.

Pink Eye (Ovine Keratoconjunctivitis)

This infectious eye disease can be a big problem in some flocks, causing runny, reddened eyes, cloudiness of the cornea and sometimes more serious corneal damage. If both eyes are badly affected the animal can become temporarily blind and disoriented. The main cause is a bacterium called Mycoplasma conjunctivae, though other bacteria can also be implicated. Immunity after infection is not very good, so the disease can rumble on in a flock for months. Mild cases often recover by themselves, but more severe cases need treating to avoid permanent eye damage, though this is not easy.

Antibiotic ointment needs to be applied two or three times daily, which is not very practical. The best treatment is the injection of antibiotic near the eye, which your vet will need to do. If animals are so badly affected that they cannot see, they will need to be put in a safe area such as a small paddock or loosebox, and supplied with food and water until they recover.

Fig. 582 The Texel wobbler problem may be related to the very short necks of this breed.

Silage Eye

Silage eye is a different type of eye infection caused by the same organism that causes listeriosis; it is thought to get into the eyes when sheep are rummaging in contaminated silage. Again, infected animals have painful runny eyes, this time with changes inside as well as on the surface. Treatment is also by injection of antibiotic, with steroid too, close to the eye given by your vet.

Poisoning

One of the most important causes of poisoning in sheep is due to excessive intake of copper, but eating various plants can cause illness and deaths, particularly in snowy conditions where normal grazing is covered and bushes laden with snow become within reach of hungry animals. Confirmation of a diagnosis of poisoning may require post-mortem examination, although circumstantial evidence such as obviously eaten leaves or branches is often a pointer.

Copper

We have already drawn attention to the complex relationship between copper and sheep nutrition, together with the variation in tolerance between and within breeds. Copper deficiency (strictly speaking, molybdenum toxicity) is responsible for swayback and increased mortality in newborn lambs (see Chapters 11 and 12). Copper toxicity occurs when there is too much copper in the diet, commonly brought about by feeding cattle concentrates or minerals to sheep.

Fig. 590 Do not give cattle concentrates or minerals to sheep as these contain higher amounts of copper that can easily lead to poisoning and death.

Alternatively it may occur when diets containing relatively normal amounts of copper are fed for prolonged periods, for example to show sheep, or when management is changed from outwintering to housing. This removes the intake of molybdenum and other minerals in the soil that would otherwise make copper in the diet less available.

Another cause can be dosing with copper preparations to animals that already have an adequate copper status. The end result is often sudden death, with the carcase being jaundiced, and the appearance of the liver and kidneys being typically dark. If animals are seen alive, treatment is not very rewarding, since chronic liver damage is likely. The source of the copper needs identifying and removing, and great care needs to be taken in feeding or administering anything containing copper.

Lead

Poisoning with lead occurs occasionally where sheep are grazing on ground naturally containing high levels of lead – this may be indicated by the presence of lead mines in the past. Animals may fail to thrive, and show bone deformities and fractures.

Acorns

In years when there is a large crop of acorns, problems can occur as some sheep find them very attractive to eat. Many eat them without any apparent ill effects, but some do become ill, showing constipation or dark-coloured diarrhoea, and dullness; they eventually die from kidney damage.

Fig. 591 Some sheep eat acorns with relish, but they can sometimes be poisonous.

Bracken

Cattle are more susceptible to bracken poisoning than are sheep, but occasionally long-term intake causes blindness, referred to as ‘bright blindness’. This is irreversible, as the retina at the back of the eye is permanently damaged. Eating bracken over an extended period has also been associated with tumour formation, for example, in the jaw and bladder.

Ragwort

Sheep do not normally eat ragwort, but they may do so if grazing is sparse or if hay containing the plant is fed. It causes chronic liver damage, loss of weight and death.

Laurel and Rhododendron

Poisoning with laurel and rhododendron usually occurs in bad winter weather when normal food is not available, or sometimes if garden waste is thrown into fields where sheep are grazing. Both cause collapse and death, with rhodendrons specifically causing attempts to vomit.

Yew

Yew is usually considered to be almost instantly fatal if eaten, but there have been reports of sheep surviving eating it in bad winter weather.