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 |
EAEEnzootic 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
|
MVMaedi-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 |
CLACaseous 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 |
BDVBorder 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.
Comments are closed.