NADIS disease forecast (sheep) – May

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.

NADIS disease forecasts are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare. The forecasts are based on national trends and farmers are advised to discuss their individual farm circumstances with their veterinary surgeon .

May 2005


NADIS Sheep Disease Forecast

Weather conditions have a major effect on the seasonal pattern of sheep production limiting diseases, and summary of the situation throughout the UK sheep can prove to be difficult when it is based mostly on experiences from one part of the country.  Weather conditions in the south-east of Scotland during the latter part of April and first two weeks of May were mostly cold, with drying northerly winds. 

As a result, few problems associated with nematodirosis or other helminth worms were encountered, but the incidence of mastitis in ewes was high, associated with poor pasture growth causing ewes to go off their milk.  Two days of awful weather conditions at the end of April, with cold winds and heavy snowfall resulted in substantial and upsetting lamb losses due to primary hypothermia in many flocks in the south-east of Scotland.  Some sheep farmers in the south-east of Scotland were still supplementing their April-lambed ewes with concentrates during the second week of May.  The situation elsewhere in the UK would appear to have been different, with high risks of nematodirosis published in the farming press. 

Mastitis in ewes
The early signs of acute mastitis in ewes are failure to eat and lameness in the hind limb on the same side as the affected half of the udder.  Unfortunately, these signs are easily missed at this time of year, when most ewes are not receiving supplementary feed and many are lame associated with scald.  The udder is initially swollen, hard, warm and painful, but is often cold and purple-coloured by the time that cases are identified. 

Tilmicosin (Micotil) is now licensed for the treatment of mastitis in ewes and while results of large scale, controlled studies are unavailable, many sheep farmers report an excellent response to treatment in cases which are detected early, while the udder is still warm and swollen.   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.  The udder of surviving ewes usually sloughs to reveal finger-like protrusions of deeper glandular tissue, which become secondarily infected and fly-struck.  These cases present an unacceptable welfare concern. 

In less severe cases of mastitis, 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.  These cases often go unrecognised during the initial stages of the disease, but are 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 Mannheimia (Pasteurella) haemolytica.  S. aureus is present on the teats of all ewes and M. 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.  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.

Orf lesions around the base of the teats or exposure of the teats to cold winds are often reported to predispose to mastitis.  In reality, orf-like lesions around the base of the teats are usually caused by bacteria such as Staphylococcus aureus, associated with lamb sucking behaviour due to poor milk production, while the primary effect of cold winds is to stop ewes from feeding, thus reducing their milk supply.  It is important, therefore, not to dismiss outbreaks of mastitis as being due to unmanageable factors such as orf and cold winds, but first to address the potential primary problem.

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.

Joint ill
The incidence of joint ill in 2 to 4 week old lambs has been particularly high this year, characterised by lameness with pain, heat and fluctuating swelling of several limb joints, leading to poor sucking behaviour and ill-thrift.  Recent articles in the farming press have indicated that outbreaks of joint ill might be associated with infection due to the bacterium Erysipelas rhusiopathiae, which might be prevented in future years by vaccination.  However, while E. rhusiopathiae joint ill can cause serious annual losses in a few flocks, most cases are caused by non-specific bacterial infections such as Escherichia coli and Arcanobacterium pyogenes. 

Joint ill associated with non-specific bacteraemias
High incidences of joint ill are associated with inadequate or poor quality colostrum intake during the lambs’ first few hours of life, and a high level of environmental contamination.  Cold and wet weather over the lambing period and the use of poor quality, damp straw for housed ewes would have contributed to the particularly high incidence of the problem this year. 

In advanced cases of joint ill associated with non-specific bacteraemias, with obvious distension of several joints, the treatment response to prolonged courses of antibiotics and anti-inflammatory drugs is poor.  In most situations, the most appropriate management is to humanely euthanase severely affected lambs, with attention focused on prevention of similar problems in subsequent years.  Prevention depends on ensuring good maternal nutrition, control of abortion and prevention of dystocia to ensure that lambs are able to receive an adequate early colostrum feed, as well as ensuring adequate hygeine of the lambing environment, for example by –
– employing sufficient skilled assistants to monitor all neonatal lambs, to detect and investigate disease and instigate early treatment 
– installing good access to lambing pens and good lighting
– aiming for a compact lambing period to maximise the use of labour and minimise the potential for build-up of disease in the lambing environment.  This strategy depends on correct feeding of ewes and rams pre-mating and a good ram:ewe ratio
– maintaining strict hygiene of lambing accommodation.  In the case of housed ewes, it is important that both the lambing courts and individual pens are kept clean, to minimise contamination of ewes’ fleeces and udders.  Buildings should be well ventilated and drained.  Individual pens should be well-lit, easily accessible and cleaned between occupants.  Hoggs and long-tailed ewes should be dagged prior to entering lambing accommodation. Daily application of paraformaldehyde granules to the bedding is advocated by some authors
– ensuring that the stocking rate of housed lambing accommodation doesn’t exceed one ewe per 1.1 m2 .  Provision of one individual pen per 8 housed ewes is recommended
– dipping all lambs’ navels in strong iodine solution at birth (and again four hours later).  Dipping is preferable to spraying with oxytetracycline
– ensuring that all lambs receive adequate colostrum within the first 4 hours of life.  If in doubt, administer 50 ml/kg of colostrum or colostrum substitute by stomach tube
– ensuring that hot water and a full clean lambing kit is easily available
– checking all penned lambs regularly for signs of brightness and full stomachs.  Navels should be brittle by 36 hours-old

Streptococcus dysgalactiae joint ill
During recent years, Streptococcus dysgalactiae has been identified as an important cause of joint ill in lambs less than 4 weeks old.  In the acute stages joints are not grossly distended, with enlargement due to pus appearing as a chronic feature.  It is thought that lambs acquire infection in the first 2 weeks of life, perhaps from the teats or milk of a carrier ewe, although this is not proven.  The bacterium survives very well on dry straw and wool, so infection may be from a heavily contaminated environment.  Morbidity rates can be high, despite good hygiene and colostrum management.  The disease is often seen in both lambs from a pair of twins.  In many flocks, the disease recurs in subsequent years.

Erysipelas rhusiopathiae joint ill
E. rhusiopathiae has a wide host range and can survive for long periods in the soil, especially at low temperatures.  Recently born lambs acquire the infection in the same way as they acquire other forms of joint-ill.  Older lambs usually become infected via docking or castration wounds or abrasions acquired through dipping (post dipping lameness).

In neonatal lambs, a bacteraemia results in organisms settling in the joints, where they cause a fibrinopurulent polyarthritis in addition to osteomyelitis and in some cases endocarditis.  Morbidity can reach 40%, although mortality is low.  Affected lambs are stiff and may have high rectal temperatures.  In the early stages, the joints are not markedly swollen.  If untreated, the disease becomes chronic and results in serious ill-thrift.  By this stage, the joints are markedly swollen and may be ankylosed. 

In early stages, treatment with high doses of parenteral penicillin is effective.  Control requires good husbandry and management.  In addition, in flocks with a recognised problem, vaccination of the dam with two doses of bacterin, 4 – 6 weeks apart in the first year and one booster dose 3 – 4 weeks before lambing in subsequent years is effective. 

The underlying cause and management of joint ill depends on the specific bacterial cause of the problem.  Your vet can reach a specific diagnosis, based on the clinical signs, postmortem findings and bacterial culture of pus or fibrin from affected joints.  A blood test is available to assist with the diagnosis of chronic joint ill caused by E. rhusiopathiae.  

Pasteurellosis in lambs
There were several reports of ill thrift and death in 4 to 6 week-old lambs caused by Mannheimia (Pasteurella) haemolytica.  Pasteurellosis resulted in the loss of 2% of the lambs in an upland flock in the south-east of Scotland.  This unusually high incidence of this problem would have been associated with the predisposing stress factors of periods of cold and wet weather, rather than new introduction of infection to the flock.

The postmortem findings are usually characteristic, with areas of lung consolidation, pleurisy, pericarditis and peritonitis, often with fibrin tags on the surface of the liver.  Confirmation of the diagnosis is based on culture of the causative bacterium from these sites.

Many of the reported cases were in lambs which had been born to dams which were boosted with Heptavac P Plus 4 to 6 weeks before lambing.  Unfortunately, while this modern vaccine provides good protection against the biotypes of M. haemolytica which are most commonly involved, passive immunity in the lambs is short-lived and usually wanes by about 4 weeks-old. 

Lambs can be actively immunised from 10 days old, using two injections of a Pasteurella/Mannheimia vaccine 3 to 4 weeks apart.  However, active immunity is also short lived, and the potential for further losses seldom justifies the cost and impracticalities involved.  Whole flock antibiotic treatment for the control of bacteraemic pasterurellosis in grazing lambs is unproven and unlikely to be practical. 

Your vet can diagnose the cause of lamb deaths in your flock and advise you about their prevention.  Unfortunately, little useful practical advice can be afforded for the control of bacteraemic pasteurellosis, which is essentially a stress-related disease. 

High barren rates
At the end of April, a group of upland ewes which had not lambed during the first 4 weeks of the lambing period, and were not obviously pregnant, were ultrasound scanned to determine whether or not they were pregnant.  40 ewes (about 10% of the flock) were identified as barren. 

The target barren rate for upland ewes following a two-cycle (36 day) mating period is 2%, although up 4% is accepted in most flocks.  Subsequent investigations showed the cause of the 10% barren rate to be multi-factorial.  About 10 ewes were thought to have aborted or resorbed their lambs, and several barren gimmers had high Toxoplasma gondii antibody titres, suggesting, but not proving, that they were barren due to toxoplasmosis.  The gimmers had not been vaccinated with Toxovax due to unavailability of the vaccine before the mating period.  Several of the barren ewes had been mated in the same group, suggesting, but not proving the existence of a subfertile ram.  However, about half of the barren ewes were in poor body condition associated with broken mouth.  These ewes had been retained to enable expansion of the flock. 

While the cost of maintaining non-productive ewes would previously have been offset by their ability to generate subsidy income, this is no longer the case.  With the implementation of the single farm payment, it is now important to ensure that all ewes in the flock are productive and retaining potentially non-productive older ewes could prove costly.  If a decision is made in future years to retain older, broken mouthed ewes, then they should be scanned during mid gestation and culled if not in lamb or in poor body condition, rather than remain unproductive but requiring feeding throughout the late pregnancy period.

Kangaroo gait
Several cases of kangaroo gait were reported in lactating crossbred ewes.  Kangaroo gait is usually seen in inadequately fed ewes suckling twins, but the cause is unknown.  Affected sheep show difficulty in placing their forelimbs and move with shortened strides with their hindlimbs drawn under the body.    Most affected animals recover when their lambs are weaned.

Your vet can advise you about the diagnosis, treatment, management and prevention of metabolic diseases in your lactating ewes.

Pulpy kidney in lambs
There were a few reports during the first two weeks in May 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.

The list of other problems reported in young lambs during the second half or April and beginning of May includes :-

• orf in lambs
• lameness in lambs due to scald and thorn injuries q scald and footrot in adult sheep
• listeriosis in lambs and in adult sheep
• Johne’s disease
• unconfirmed outbreaks of coccidiosis in lambs
• so-called “wobbler syndrome” in Texel rams
• King’s evil (actinobacillosis
) in ewes
• rectal and vaginal prolapse in ewes

Copyright © NADIS 2005

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.


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