NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases of cattle, sheep and pigs in the UK.
By Neil Sargison BA VetMB DSHP FRCVS
NADIS Sheep Disease Forecast
Sheep veterinary work during May and the first half of June was extremely quiet, associated with mostly warm and dry weather.
There were fewer reports during this period of nematodirosis and parasitic gastroenteritis (teladorsagiosis) than during recent years (these diseases were described in the NADIS report for May 2004).
However, two days of heavy rainfall and cold winds towards the end of June resulted in heavy losses of recently shorn ewes in many flocks throughout the south-east of Scotland.
MANY RECENTLY SHORN EWES DIED FROM HYOPOTHERMIA
There were reports of coccidiosis in lambs (the disease is described in the NADIS report for May 2004). In some cases, concern was expressed about the poor response to treatment.
Whenever a poor treatment response is suspected, the diagnosis should be reviewed. Coccidiosis is essentially a disease associated with intensive husbandry, and outbreaks in extensive pasture reared lambs are unusual.
The specific diagnosis of coccidiosis is problematic and other diseases such as nematodirosis, teladorsagisosis or even nephrosis may present with similar clinical signs.
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, and because the appearance of disease is not necessarily directly related to the presence of oocysts of pathogenic species. Confirmation of the diagnosis relies on post mortem findings.
THE DIAGNOSIS OF COCCIDIOSIS CANNOT BE CONFIRMED BY IDENTIFICATION OF OOCYSTS IN FAECAL SAMPLES
Individual lambs with coccidiosis are usually treated using injections of sulpha drugs. However, most of these drugs are no longer available, the only remaining product (sulphadimidine) requiring a very large dose (initial dose rate 13ml for a 20 kg lamb).
Coccidiosis is essentially a management related disease, so prevention should be aimed at reducing stocking density and attention to environmental hygiene, for example by regular cleaning and moving of creep feeders and application of lime to likely heavily contaminated areas around water troughs and feeders. It can be useful to keep later born lambs on different areas to early born lambs.
REGULAR MOVEMENT OF CREEP FEEDERS CAN HELP TO REDUCE THE RISK OF COCCIDIOSIS
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, so 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. Used in this way, diclazuril can prove very useful, although it is generally less effective for the treatment of clinical disease. Specific advice on the management of coccidiosis can be obtained from your vet.
There was a significant increase in the incidence of blowfly strike during May, associated with warm and muggy weather, scouring lambs and un-shorn ewes. Blowfly strike prevention was discussed in the NADIS report for May 2004.
The usual seasonal increase was seen in lameness problems in lambs. Most outbreaks were due to scald, although footrot, foot abscess, toe granulomas and thorn injury to the sole were also reported (the management of all of these diseases has been described in recent NADIS disease focus articles).
THORN INJURY (ARROW)
Scald is the most common cause of lameness in sheep, which occurs on all farms. Typically many animals in the flock are lame in one or more foot. In extreme cases, 90% of the flock can be affected. Rubbing caused by long grass can exacerbate the problem and lameness can persist for several months if untreated.
The diagnosis of scald is usually based on clinical examination of lame animals. In mild cases the interdigital skin is red and swollen and covered by a thin layer of white necrotic material.
In more severe cases, the interdigital skin is eroded to expose deeper, sensitive subcutaneous tissue. Unlike cases of footrot, there is no under-running of the hoof wall or sole and no foul smell.
SCALD – INFLAMMATION OF THE INTERDIGITAL SPACE
Uncomplicated cases of scald often recover spontaneously when sheep are moved to dry pasture, although this is seldom a practical management strategy.
Pasture around feed troughs and gateways can become trampled, muddy and heavily contaminated with faeces. Regular movement of troughs and avoidance of these areas can significantly reduce the incidence of foot diseases.
Individual cases of scald can be treated topically using antibiotic aerosol sprays. When several animals are affected, weekly walking of sheep through a 10% zinc sulphate solution or 5% formalin usually provides effective control.
Afterwards sheep should be allowed to stand in a dry area so that the formalin or zinc sulphate can dry on the feet. Failure of this strategy to control the problem often indicates the presence of footrot, which requires more radical control. Scald cannot be controlled by the use of footrot vaccines.
At concentrations greater than 5%, formalin can cause severe irritation of the interdigital space. The practice of regularly replenishing footbaths with a few splashes of concentrated solution should, therefore, be avoided.
FOOT BATHING – FORMALIN OR ZINC SULPHATE SOLUTION
Scald is also important because it is the first stage in the pathogenesis of footrot and suppurative infection of the distal interphalangeal joint (foot abscess).
In some regions lowground spring born lambs will be weaned during the next few weeks. The production efficiency of intensive lowground systems is greatest when lambs are finished as quickly as possible, because the daily feed requirement for maintenance of healthy lambs is the same as that of ill thrifty lambs, which take longer to reach slaughter weight.
Furthermore, finishing lambs quickly reduces the effect of production limiting diseases such as parasitic gastroenteritis (worms) flystrike, cobalt deficiency, lameness and pneumonia, which are usually most severe during the latter part of the grazing season.
WEANED LAMBS SHOULD BE MANAGED TO ACHIEVE OPTIMAL GROWTH RATES
There are a finite number of causes of ill thrift in lamb flocks, all of which can be identified and prevented by appropriate management. Consultation with your vet about ill thrift in lambs is therefore worthwhile.
As a general guide, when ill thrift is associated with poor lamb growth before weaning, for example due to poor ewe milk production, the problem is characterised by uneven lamb size and body condition. When the problem has arisen due to events after weaning, ill thrift is usually present in the whole group.
Important causes of ill thrift in weaned lambs:
parasitic gastroenteritis (worms)
other specific infectious and management problems such as:
• respiratory disease
• sheep scab
• border disease
Many of these causes of ill thrift can be identified on the basis of a relevant disease history, assessment of pasture and feed availability and examination of the flock for signs of lameness, coughing, scour and itching to determine the presence of specific problems such as footrot, enzootic pneumonia, and sheep scab.
However the clinical signs associated with parasitic gastroenteritis, trace element deficiencies and liver fluke are seldom specific and further diagnostic tests are usually required.
Faecal samples can be collected from 7 – 10 animals for worm egg counts, coccidia oocyst counts and/or identification of fluke eggs. Serum and blood samples can be taken for vitamin B12 and glutathione peroxidase assays for the diagnosis of cobalt and selenium deficiencies respectively.
Ill thrifty lambs may be of low financial value, so the humane destruction and post mortem examination of one or two of the worst affected animals is often a practical diagnostic tool. The postmortem examination is focussed on the common causes of ill thrift and does not require a detailed examination of all organ systems.
The procedure can confirm a diagnosis of gastrointestinal parasitism or liver fluke and provide the opportunity for the collection of useful samples for the diagnosis of trace element deficiencies.
Malnourished animals and parasitised animals are more susceptible to the effects of trace element deficiencies. In these cases, the trace element deficiency is frequently resolved when the primary problem is corrected. This confusion is avoided through the adoption of a scientific approach to determine the trace element status of animals.
Diseases of adult sheep
There were relatively few reports of significant flock disease problems in adult sheep during May and the first half of June. Cowped ewes and hypothermic recently-shorn ewes presented the greatest problem.
Several cases of acute mastitis were reported (described in the NADIS report for May 2004). A few cases of photosensitisation were seen associated with grazing lush green pasture.
COWPED EWES PRESENTED A PROBLEM DURING MAY
The list of other diseases reported during May in adult sheep includes:
inguinal hernia in a Suffolk ram
pizzle rot in a Suffolk ram
Johnes disease in Greyface ewes
jaagsiekte in a Greyface ewe
Your vet can advise you about the diagnosis and management of these diseases in your flock.
• 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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