NADIS disease forecast – sheep (June)

NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases of cattle, sheep and pigs in the UK.

NADIS data can highlight potential livestock disease and parasite incidences before they peak, providing a valuable early warning for the month ahead.

June 2004

By Neil Sargison BA VetMB DSHP FRCVS

NADIS Sheep Disease Forecast

While weather conditions for spring lambing were generally colder and wetter than during recent years, there were few NADIS reports of significant lambing-related disease problems. 

Lamb mortality rates were generally low and there were few reports of watery mouth, joint ill and navel ill in lambs. There were more reports of ewes requiring caesareans than during recent years, probably reflecting sustained optimism for the sheep industry rather than any trend towards dystocia problems.

More flock problems of pregnancy toxaemia were reported than during recent years. While some of these were associated with poor hay or silage quality, others were related to concurrent disease such as footrot. 

Management of clinical cases of footrot can prove particularly difficult in housed, late-pregnant ewes, highlighting the importance of disease control early in the year, before it becomes production limiting.

For most flocks lambing has now passed and the focus has changed to ensuring optimal lamb growth rates. 

Pasture growth has been good in most regions, but poor lamb growth rates have been reported caused by nematodirosis, coccidiosis and spring teladorsagiosis. Mastitis has been an important cause of poor individual lamb performance.

Cases of blowfly strike have been reported in south-east Scotland, significantly earlier in the year than usual.

The incidence of acute mastitis has been high in some flocks. Most cases of acute mastitis have been seen within the first 2 weeks after lambing. 

Affected ewes don’t feed and often appear lame in one hind limb. The udder is initially swollen, hard, warm and painful, but may become cold and purple-coloured within a few hours. Many ewes die as a result of generalised toxaemia. 

Those that survive are generally ill thrifty and the affected side of the udder eventually sloughs to reveal finger-like protrusions of deeper glandular tissue, which become secondarily infected and fly-struck. 

In less severe cases, the udder does not become cold and necrotic, but deep abscesses form within the udder as the acute infection subsides. Lamb growth rates and weaning weights are poor. Chronic mastitis may go unrecognised during the initial stages of the disease, but is later identified by the presence of hard swellings within the udder. 

These cases are often not detected at the time of weaning when ewes are still lactating, but are found after the subsequent lambing when milk production is poor. In problem flocks, ewes’ udders should, therefore, be re-checked before mating.

Mastitis in lactating ewes usually results from bacterial infection of the udder by the bacteria Staphylococcus aureus or Pasteurella haemolytica. S. aureus is present on the teats of all ewes and P. haemolytica is found in the mouths of most young lambs. 

Mastitis occurs when these bacteria have the opportunity to enter into the normally protective teat canal. This can occur when the ewes’ milk supply is insufficient, resulting in excessive suckling by lambs and teat injury.

Orf lesions on the teats, or exposure of the teats to cold winds can also predispose to mastitis. Occasionally other opportunistic pathogens such as Escherichia coli are involved, associated with a wet, dirty environment, or dirty hands while checking newly-lambed ewes for milk flow.

Early cases respond well to antibiotic (tilmicosin) treatment. However, the treatment response is poor where the udder is already cold, purple-coloured and gangrenous, in which case ewes should be euthanased to avoid further suffering and ill thrift associated with chronic suppurative infection. 

Prevention of acute mastitis depends on identifying the predisposing factors. In most cases the underlying cause is poor milk production, which can be addressed in subsequent years by attention to the body condition and protein nutrition of ewes during the second half of pregnancy. Your vet can help you to identify the important predisposing factors for mastitis in your flock and provide advice on appropriate management to reduce the risk.

Pulpy kidney in lambs
There have been several reports of sudden death in both ewes and lambs due to pulpy kidney.  

Effective prevention of pulpy kidney is achieved through vaccination using a multi-component vaccine containing toxoids of C. perfringens.  Vaccination of ewes protects their newborn lambs against pulpy kidney up to about 16 weeks of age. 

Previously unvaccinated ewes should be given an initial course of two injections 4 – 6 weeks apart when they enter the breeding flock, followed by an annual booster about 6 weeks before lambing. Lambs born to vaccinated dams should receive a first sensitiser dose at about 8 – 12 weeks old, followed by a second booster at least 4 weeks later. 

Vaccination should be combined with good stock husbandry, including good hygiene at lambing, the insurance of adequate early colostrum intake and careful introduction to improved planes of nutrition.

Many UK sheep are inadequately vaccinated against clostridial diseases and severe outbreaks of pulpy kidney occur sporadically. In these cases it is important to instigate a vaccination programme immediately. Where a sensitiser, but no booster dose of vaccine has been previously used, a single injection of vaccine in the face of an outbreak usually provides immediate protection. 

Even when no vaccine has been used, a single injection of vaccine offers significant protection within 48 hours, probably because most animals are naturally sensitised by the presence of small amounts of toxin in their intestines. 

Yarding of animals for vaccination and restricted feeding usually halt the progress of the disease until the vaccination programme is complete. Your vet will be able to provide more specific advice on the control of clostridial diseases.

Blowfly strike
Fly struck sheep appear restless and repeatedly bite or kick at the affected area. Lambs are typically affected over the hindquarters and perineum, associated with faecal contamination, but can be struck at other sites. 

On close examination, the wool overlying struck areas is discoloured, moist and foul-smelling.

During the early stages, the maggots, which are approximately 1.5 cm long, are only visible, end-on, when the wool is parted, but as the disease progresses, the wool falls out to reveal the underlying affected tissue. Unless promptly recognised and treated, tissue degradation products and maggot secretions can result in toxaemia and death. 

Most of the blowfly lifecycle occurs off the sheep. Flies over-winter in the soil as pupae, which emerge as soil temperatures rise during the spring. 

Blowfly populations are greatest during the summer months, when given favourable conditions of humidity and warmth, the entire life cycle from egg to adult occurs in less than 10 days.

Despite a good understanding of blowfly biology, the effective prevention of flystrike remains problematic. 

Blowflies can travel for several miles, so unlike lice and scab mites, they cannot be eradicated from a farm. Furthermore, while modern insecticides are extremely effective, in practice correct application of these drugs to achieve satisfactory residual activity is difficult.  

The effective control of flystrike is seldom achieved by the use of insecticides alone. Freshly dead animals, faecal material and rotting vegetation provide protein for blowflies, so the prompt burial of carcasses and attention to general farm hygiene can aid in their control. 

Blowflies prefer a warm, moist and sheltered environment, so moving sheep to more exposed pastures can reduce the risk of strike. The smell of wool grease and the presence of foot rot, urine soaked wool, skin diseases, scour, or infected cuts attract blowflies to sheep. 

Established strike lesions attract even more blowflies. Recently shorn sheep are seldom struck and effective control of gastrointestinal parasites and footrot, general animal health care, crutching and trimming around the pizzle can further aid in the control of flystrike.        

The choice of dip chemical is partly governed by the length of protection required, which varies from as little as 2 weeks for some organophosphate plunge dips up to 16 weeks for the insect growth regulator pour-on, dicyclanil. Your vet can advise you about the best method of flystrike control for your flock.

Fly struck sheep need to be treated immediately. Struck areas are sensitive to sunburn, so should not be clipped other than to gain access to the wound. 

Application of an organophosphate or high-cis cypermethrin dressing will then kill the maggots and protect the surrounding skin from secondary strike. 

If plunge dip solution is used, it should be diluted to normal dip strength. Insect growth regulators (cyromazine and dicyclanil) are ineffective for the treatment of established flystrike.

Weather conditions during April were generally warm and wet enough to allow most Nematodirus battus eggs to hatch.  Thus there is a risk of nematodirosis in spring-born lambs grazing on pastures used by young lambs last year.

Nematodirosis is usually seen in young lambs and is characterised by acute onset profuse watery diarrhoea, lethargy, abdominal pain rapid weight loss, dehydration and sudden deaths.  

The life cycle of N. battus differs importantly from the other gastrointestinal parasites of sheep. Infective larvae develop within the parasite egg and can survive freezing and very low temperatures on pasture for a period of up to 2 years. 

Hatching and release of infective larvae only occurs after a period of cold exposure followed by daily maximum temperatures above 10oC. 

Such conditions usually occur during May and June, when infective larvae can appear en masse.  When this hatch coincides with the presence of susceptible grazing lambs, it can result in the appearance of acute disease. 

The life cycle of N. battus involves only lambs (and occasionally dairy calves) and the accumulation of infection on pasture takes place over a period of several years of grazing by susceptible animals. Lambs which are grazed on pastures used for young lambs last year are at greatest risk. 

Most of the modern wormers are effective against N. battus, with the exception of injectable moxidectin. However, none of the wormers available in Britain provides persistent protection against N. battus, so during high risk years two or three anthelmintic treatments may be required before weaning.

There have been several reports of coccidiosis in 3 to 6 week-old lambs characterised by acute onset diarrhoea, dullness, anorexia, dehydration and weight loss affecting a high proportion of the lamb flock.

Outbreaks of coccidiosis in sheep are caused by two species of sheep specific protozoan parasites. Following the ingestion of coccidia oocysts from a contaminated environment, the parasite invades and multiplies in the cells of the lining of the intestine. After a period of 2 – 3 weeks oocysts are shed in the faeces, further contaminating the environment. 

Under suitable damp conditions many oocysts survive over winter in buildings and on pasture. Oocyst shedding by healthy ewes also contributes to the environmental contamination. Coccidiosis is essentially a disease of intensive husbandry and the severity of disease is proportional to the level of environmental oocyst contamination.

Early born lambs may not ingest sufficient oocysts to become clinically affected, but contribute significantly to the contamination of the environment and disease in later born lambs.

The diagnosis of coccidiosis is based on the history of intensive lamb management and clinical signs. The important differential diagnosis is gastrointestinal parasitism, in particular nematodirosis in young grazing lambs. 

Faecal oocyst counts may support a diagnosis of coccidiosis, but alone are of limited diagnostic value, because many species of coccidia may be present without causing disease. The diagnosis is usually confirmed by post mortem findings.

Outbreaks of coccidiosis in lambs are usually managed by whole flock treatment with sulpha drugs and avoidance of intensive grazing. It can be useful to keep later born lambs on different areas to early born lambs.

The coccidiostat drug decoquinate can be included in lamb creep feed for the prevention of coccidiosis, or fed to ewes to reduce their contribution to environmental oocyst contamination. However, this strategy doesn’t enable good development of immunity and there is a danger of disease when the medication is stopped. 

Diclazuril can be administered orally to lambs as a single preventive treatment in anticipation of a problem. Specific advice on the management of coccidiosis can be obtained from your vet.

Parasitic gastroenteritis (worms)
There have already been several reports of spring teladorsagiosis in 8 – 10 week-old lambs associated with grazing on pasture which is heavily contaminated with over-wintered worm larvae. This appears to be an emerging problem which is related to prolonged grazing seasons associated with recent mild winters.  
Numbers of infective nematode parasite larvae on pasture will rise rapidly over the next two months. Susceptible sheep grazing on contaminated pasture invariably suffer from production losses through reduced growth rates. 

The aim of effective nematode parasite control during the spring should have been to limit the exposure of susceptible lambs to significant burdens of infective larvae on pasture. When safe grazing is available for lambs at weaning, they should be wormed before moving. 

Further anthelmintic treatments should not then be necessary until autumn, by which time most of the lambs may have been sold. 

When safe grazing is not available, anthelmintic treatments will probably need to be repeated throughout the summer months. The frequency of summer anthelmintic treatments will depend on the persistence of the product used. 

Non-persistent wormers (white drenches, levamisole, ivermectin and doramectin should be used at about 4 week intervals, while the dosing interval can be extended to 6 – 8 weeks if the persistent wormer, moxidectin is used. 

There are no simple recipes for the control of parasitic gastroenteritis. Your vet can provide advice about the sustainable control of the disease on your farm.   

There were several reports last year of poor production in lambs associated with helminth resistance to wormers. In some areas, benzimidazole (white drench) resistance is estimated to be present in 80% of sheep flocks. 

Levamisole resistance is also present and multiple resistance to all three wormer groups has now been seen in a few Scottish sheep flocks. It would therefore be prudent to check for the presence of wormer resistance in your flock. 

Bulked freshly voided faecal samples from 7-10 animals should be collected 7 – 10 days after worming (except where moxidectin has been used) and submitted to your vet for egg counting. Samples of about 2 grams (about a half of a teaspoonful) can be easily collected when sheep are disturbed and moved into the corner of a field. 

Positive post-treatment faecal egg counts indicate that the drench was not 100% effective, although an assumption is made that adult egg-laying parasites were present before drenching.

Rhododendron poisoning
Two separate cases of rhododendron poisoning were reported in the south-west of Scotland. 

Rhododendrons and Azaleas contain toxic compounds have effects on the circulatory, respiratory and nervous systems. 

Ewes usually avoid rhododendron plants and poisoning outbreaks are most commonly seen following periods of heavy snowfall when they are forced to graze on hedges. 

However, other possible predisposing factors include a move on to a field to which young sheep are unaccustomed, poor grazing management, or indiscriminate grazing by tired and hungry animals following transportation.

Clinical signs commence a few hours after the plant is eaten.  The first signs are excessive salivation, the presence of greenish froth around the mouth and nose and severe abdominal pain.  Some ewes appear to be unconscious, while others are recumbent, but excitable and make repeated unco-ordinated attempts to stand. 

These incidents are sometimes followed by unsuccessful attempts to vomit, during which the ewes adopt a “dog-sitting” position, extend their head and neck upwards and make loud, distressed, grunting noises. 

Most affected sheep recover after a few days, while some have a more prolonged recovery period or die after 3 to 7 days, usually due to secondary pneumonia. 

In common with many plant poisonings, the outcome of the disease is determined by the amount of toxin ingested, but in the early stages it is not possible to determine which sheep have ingested the most toxin. 

Several treatment regimes have been recommended, including use of purgatives and stimulants, but there is little evidence to show that any of these are successful. 

When provided with supportive therapy, most cases recover within 7 – 14 days. Administration of fluids by stomach tube evokes a painful nervous response, so should be avoided.

• While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions. All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon.

Copyright © NADIS 2002

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