Download BPA-2007-Neuro_Article

NEUROLOGICAL DISEASES IN SHEEP
Diseases affecting the nervous system can lead to a number of different clinical
syndromes – blindness, depression, behavioural changes, circling and difficulty walking
or standing are just some of the symptoms which may be seen. Sheep of all ages can be
affected by a great number of different neurological diseases, as outlined in the following
article.
METABOLIC DISEASE
Perhaps the most significant of neurological disorders, metabolic disease tends to affect
adult sheep, particularly around lambing time.
Pregnancy Toxaemia/Twin Lamb Disease
This occurs in late pregnancy in ewes carrying multiple lambs. It usually affects thinner
ewes that have not received enough concentrate. The first sign is usually loss of appetite,
the ewe separating herself off, standing still and seeming blind.
 Treatment should be immediate – drench with Twin Lamb Drench or Ketol.
Repeat in a few hours and offer good hay and some concentrates.
 If the ewe does not respond in a few hours, veterinary assistance should be sought
for the administration of intravenous medication
 Control of this condition can be achieved by condition scoring ewes, separating
ewes below CS3 and feeding good quality concentrate. Scanning for lamb
numbers will also help predict which ewes are likely to need a higher level of
feeding.
Hypocalcaemia
In contrast to the equivalent condition in cattle (milk fever), disease tends to be seen in
late pregnancy rather than early lactation. Ewes in any condition can be affected,
particularly following stress such as gathering for housing or vaccination. Ewes have
difficulty walking or lie down, are depressed and may develop bloat.
 The condition worsens over hours, resulting in death, so should be treated straight
away. Some ewes will respond to 50-100ml calcium 20% (blue top) under the
skin.
 If this does not cure the problem, veterinary examination is required for
intravenous calcium administration
 Control can be difficult – watch the flock closely after gathering etc and have
calcium injection handy
Hypomagnesaemia
This nearly always occurs at peak lactation. Lush grass is low in magnesium so ewes are
particularly at risk when grazing this pasture. Signs come on very rapidly: excitability,
shaking and convulsions. Death follows rapidly so ewes are often found dead.
 If cases are found, give 50ml Magnesium Sulphate (black top) under the skin
 If ewe does not recover, veterinary treatment is required
 Watch the flock closely after moving onto lush pasture and have magnesium
injection handy. Magnesium supplementation can be given by enriched cake,
rumen bullets or licks in high risk flocks.
SCRAPIE
Scrapie is a Transmissable Spongiform Encephalopathy (TSE), a fatal brain disease in the
same bracket as BSE in cattle. It has the potential to infect humans, and as such
controlling it is of great importance. It is a notifiable disease i.e. any suspected cases must
be reported to the local Animal Health Divisional Office (AHDO).
Scrapie is an infectious disease. The way in which it is spread remains unclear, however
it is known that infection is resistant to most disinfectants and can persist in the
environment for many years.
There is a long delay between infection and clinical disease, so cases tend to arise in
older animals (usually around 3½ years old), with only 1 or 2 individual sheep being
affected at a time. Clinical signs include scratching, nervousness, depression, loss of
coordination, weakness and becoming unable to stand. The condition is untreatable so
the eventual outcome is death.
How can it be controlled?
The different genetics of different sheep affects how likely it is an individual will develop
scrapie. This can be assessed by a blood test. The genotype which is most resistant to
scrapie is ARR and the most susceptible is VRQ. By breeding only from the more
resistant genotypes, the national flock will, over the years, become less at risk of this
serious disease. This is the concept behind the National Scrapie Plan (NSP).
National Scrapie Plan
This government-funded initiative was set up in July 2001. The scheme is voluntary and
is mainly focussed on rams. Funding is currently under review and is likely to be altered
from Spring 2008.
Since the start of the NSP:
 Most resistant (ARR) genotype of rams in tested flocks have increased by 37%
 Most susceptible (VRQ) genotype has more than halved
 Five-fold reduction in the amount of scrapie seen in abattoirs (2006 survey) as a
knock-on effect in the national flock
 Up to date information is available via the DEFRA website at
www.defra.gov.uk/nsp
LISTERIOSIS
This disease, causing depression, drooping of the ear/eyelid and circling, is associated
with the feeding of silage. Poor quality, high pH silage, which has been air-spoiled or
contaminated with soil, carries most risk. Treatment, with antibiotics, is usually
unsuccessful with the eventual outcome being convulsions and death.
GID CYST
This condition is caused by the larval stage of the dog tapeworm. Sheep are infected via
dog faeces. Once in the sheep’s bloodstream the larvae migrate to the central nervous
system and develop into a cyst. Neurological symptoms will develop, the exact signs
depending on the position of the cyst in the brain. The symptoms will worsen as the cyst
grows larger, eventually leading to death. Cysts can be surgically removed, but
prevention is preferable:
 Worm dogs against tapeworm at least every 3 months
 Dispose of sheep carcases properly
 Avoid sheep grazing heavily infected pasture e.g. following sheepdog trials
LOUPING ILL
Louping ill is caused by a virus and is transmitted by ticks. As such the disease is only
significant in stock grazing tick pasture e.g. rough upland.
 Following infection, the virus travels via the blood to the brain where it
multiplies, causing disease 6-10 days later. Only 5-60% of infected sheep show
clinical signs, with stress (such as gathering, severe weather, concurrent disease)
making disease more likely. The severity of disease can also be quite variable.
 Clinical signs include nervousness, difficulty walking, paralysis, coma and
sometimes death.
 Animals which survive infection will become immune for life.
A vaccine is available. It is expensive but should be considered if Louping ill is
confirmed. Programmes to reduce tick populations can also be considered in serious
outbreaks.
SWAYBACK
This is a disease of lambs, as a result of ewes having had low copper concentrations in
late pregnancy. Signs may be present at birth, develop within a few days or not become
apparent until lambs are several weeks old. Lambs have difficulty walking, sometimes
appearing to have paralysed hindlimbs. They will often be able to suck and graze
normally.
Copper may have been insufficient in food or pasture, or may have been ‘locked up’ by
other minerals in grass and soil. Suspected copper deficiency must be treated with
caution as too much copper is poisonous.
BORDER DISEASE / HAIRY SHAKER LAMBS
Border Disease (BD) is caused by a virus closely related to that causing Bovine Viral
Diarrhoea (BVD) in cattle. The classic example of BD infection is the ‘Hairy Shaker’
lamb, which as the name suggests have a long hairy coat and trembling muscles. Most
grow slowly and fail to thrive.
 Hairy Shaker lambs are the result of ewes meeting the BD virus for the first time
in the first 85 days of pregnancy.
 Most commonly this results in abortion but occasionally the unborn lamb
survives, though never recognises the virus as a virus. It therefore doesn’t mount
an immune response and so is persistently infected (PI), is likely to be weak, and
will continually shed virus.
 Not all PIs are weak and hairy – they may go on to breed, perpetuating the
problem.
It is often advised to cull the entire lamb crop if BD is confirmed in a flock for the first
time. Alternatively blood sampling the flock can be performed to determine which
animals are infected.
In endemically infected flocks, it may be more practical to deliberately expose all future
breeding stock to the virus. This is a crude form of vaccination, achieved by mixing
future breeding stock with Hairy Shaker lambs. This should be carried out a minimum of
2 months before tupping. Close herding for at least 3 weeks and preferably indoors is
necessary for BD virus to be spread effectively.
DAFT LAMB DISEASE
This disease is thought to be hereditary and is seen most in Border Leicesters. It is
usually seen at birth or within the first few days of life, with lambs being mentally slow
and wandering aimlessly. Badly affected lambs will not be able to suck so should be
culled.
CEREBROCORTICAL NECROSIS (CCN)
This mainly affects lambs 2-6 months old, due to a deficiency of thiamine. Lambs
‘stargaze’ and wander for a few hours, then after a short period will become more
excitable and develop tremors and fits. Lambs are often found dead as the disease can
progress very rapidly. Some cases respond to vitamin B injections.