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Infectious Diseases in Sheep

Rose Young BVM BVS MRCVS, Molecare Veterinary Services

Those involved in the sheep industry may be aware of some of the infectious diseases that can affect our national flock; you will have seen the “MV accredited” sheds at regional livestock shows, and many farms have unfortunately seen the consequences of Enzootic Abortion, often via bought-in animals. But how much do you know about these diseases in sheep? And how much risk do they pose to the average farm? This short article aims to answer those questions, and provide some practical solutions to help you and your vet minimise the risks to your stock.

‘Hidden’ diseases

There are several infectious diseases affecting sheep which could be described as hidden; in which an infected animal may appear normal for a long period (sometimes years) before showing signs of disease, or those which result in animals becoming permanent “carriers” of disease. These conditions pose a problem, in that there may be no outward signs at all in the affected animal, or simply vague symptoms such as weight loss or chronic mastitis, which can easily be put down to other causes. If you are buying in animals without knowing their disease status, you could be buying in all kinds of problems. Similarly, if you don’t know the status of your own sheep, your own home-bred “closed” flock could be harbouring diseases which may affect fertility, growth rates and overall health.

Disease

Symptoms in individuals

Symptoms in flock

Cost to the farm

National prevalence

Control options

EAE

Enzootic abortion/ chlamydia

Abortion in first year of infection

Subsequent carrier status

Flurry of abortions following entry, abortion storm next year Around £85 per abortion Common – top three causes of abortion Vaccination

Biosecurity

Accreditation

Toxoplasmosis Abortion in first year of infection

Subsequent immunity

Abortions reduced scanning %

Weak lambs

Around £85 per abortion

High barren %

Common – top three causes of abortion Vaccination

Biosecurity

Cat control

CODD Contagious Ovine Digital Dermatitis

Severe foot infections, beginning at the coronary band High numbers affected

Poor recovery

 

Production losses

Treatment

Replacement

Present in 35-50% of flocks

Affects up to 50% individuals in an outbreak

Biosecurity & quarantine

Strict culling policy

 

MV

Maedi-visna

Long incubation

Wasting

Pneumonia

Mastitis

Arthritis

Permanent infection

High, early cull rate due to wasting

Poor flock fertility

Poor overall health

Production losses

Cull/replacement rates

Present in 3% UK flocks

25% infected in positive flocks

Accreditation

Test and cull eradication policy

CLA

Caseous Lymph-adenitis

Long incubation

Common in rams

Firm cutaneous abscess

Internal abscess

Wasting

Unlikely to cure

High culling rate

High mastitis rates

Reduced longevity

Production losses

Cull/replacement rates

Approx. 18% flocks affected – likely to be higher Biosecurity (esp. at shearing)

Quarantine

Test rams pre-purchase

Test and cull

BDV

Border Disease Virus

Ewes unaffected

Lambs stillborn or abnormal at birth

Surviving lambs persistently infected

Abortions esp. in first year

High barren %

Reduced lambing %

Reduced flock health

Production losses

Cull/replacement costs

Likely under-estimated

Top ten causes of abortion

Test and cull persistently infected animals

Test incoming stock

Johnes disease (as seen in cattle)

Long incubation

Wasting

Bottle jaw

Occasional scour

No cure

High cull rate

Reduced longevity

Production losses

Cull/replacement costs

Unknown flock %

Up to 10% individuals affected in positive flocks

Testing cull/bought-in ewes

Vaccination an option for positive flocks

Resistant parasites

Unmanageable worm (and fluke) burdens – weight loss, scour, death if severe Persistent parasitic gastro-enteritis despite treatment

Increased frequency of treatment

High production losses

Treatment costs

 

1BZ, 2LV, 3ML – resistance common and widespread

TBZ (fluke) – resistance increasing

Drench testing

“Clear-out” treatments

Pasture management

Quarantine and group 4 treat new stock

 

Investigation and control

The table above shows the breakdown of key information on eight specific conditions, but you may notice that control strategies are similar across many of these diseases. The most important factors come down to three main points;

Know your status – annual or biannual cull ewe blood testing can be an excellent marker of the range of infectious diseases circulating in your flock, be sure to test abortions and seek advice from your vet if you suffer unusual production losses or health issues in the flock. MV and EAE accreditation also available.

Purchase policy – unless you have a completely closed flock, you risk buying in disease with every purchase, either buy from farms known free of disease, or arrange for a sample of animals to be tested at the source farm before entering your holding, rams especially. Quarantine and testing after arrival is an option if necessary.

Quarantine/biosecurity protocol – some (not all) of the diseases discussed above can be limited by using a sound quarantine and strategic treatment protocol, discuss with your vet to see what’s needed on your farm. Robust biosecurity prevents access between your stock and neighbouring farms and should be a priority.

 

For more information phone us on 01392 872934.