Biosecurity measures to prevent introduction of important
diseases, such as ovine pulmonary adenomatosis (also known as OPA,
SPA, and Jaagsiekte) are inadequate on many sheep farms.
However, farmers must not forget the large number of highly
efficacious vaccines without which intensive sheep farming would
prove very difficult indeed. The two most effective vaccines used
in sheep are Clostridial and Pasteurella vaccines
(often used in combination).
Industry figures consistently show farmers spend £3.50-£5 per
ewe on vet and medicines every year - what is your money spent on,
and does it provide a benefit:cost? There are few
flocks where vaccination against the most common diseases would not
prove to be financially beneficial in addition to animal welfare
Fig 1 Are so many losses over several days not an
animal welfare concern?
Clostridial diseases remain a serious threat to unvaccinated
sheep; death occurs within hours of rapid bacterial multiplication
and exotoxin production although lambs with tetanus can survive for
several days. There are long-established vaccination protocols
using toxoid vaccines which prevent all common clostridial diseases
in sheep. Initially, two vaccinations are given four to six weeks
apart followed by annual vaccination four to six weeks before the
expected lambing date to ensure adequate accumulation of protective
immunoglobulins in colostrum. Lambs are vaccinated from three
to four month-old with the programme complete before weaning unless
sold for slaughter before waning of maternal antibody at around
four to five month-old. All cases of clostridial disease are fatal
despite treatment except for a small percentage of cases of
malignant oedema (bighead) and blackleg which receive
veterinary treatment during the very early stages of disease.
The more common clostridial diseases are lamb dysentery,
tetanus, pulpy kidney, black disease, blackleg, struck and
braxy. Large losses can be experienced when sheep are not
correctly vaccinated therefore it is surprising that a UK survey
revealed that almost 20 per cent of sheep farmers did not vaccinate
their sheep on a regular basis.
Sporadic cases of clostridial disease may occur in the flock in
those lambs which have received nil or inadequate specific antibody
in colostrum due to various factors including individual ewe not
correctly vaccinated, lack of colostrum accumulation in the ewe's
udder due to poor feeding/mastitis, large litter, or feeding
colostrum supplements/bovine colostrum from unvaccinated
Fig 2: Lambs affected by lamb dysentery are
typically found dead without any observed clinical
Lambs less than one week are
affected at the beginning of the outbreak (Fig 2), thereafter
losses occur in older lambs. Lambs are typically found dead without
any observed clinical signs.
Fig 3: Pulpy kidney occurs from six months-old when
passively derived antibody has waned and the lambs themselves have
not been vaccinated.
Pulpy kidney occurs in four to ten
week-old lambs born to unvaccinated dams, and in weaned lambs from
six month-old when passively derived antibody has waned and the
lambs themselves have not been vaccinated. The major clinical
feature is sudden death (Figs 1 and 3).
Braxy is characteristically
seen in unvaccinated weaned lambs during the winter months
associated with ingestion of frosted root crops. Affected sheep are
almost invariably found dead.
Black disease is typically
associated with migration of immature liver flukes during late
summer/early autumn and can affect unvaccinated sheep of all ages.
Clinical signs are rarely observed and sheep are simply found
Entry of clostridia
occurs through skin wounds, dog bites, shearing cuts, via
contaminated needles/injection equipment, untreated umbilicus, and
trauma to the posterior reproductive tract during attempted
dystocia correction. Typically, affected sheep are very dull,
inappetant, and have a fever (>41.0°).
Involvement of one limb results in sudden onset severe
Fig 4: Bighead affecting a Texel shearling
Malignant oedema is typically seen
in rams during late summer/early autumn when head butting is a
common behaviour. The most obvious clinical sign is marked swelling
of the head particularly surrounding the eyes which forces the
eyelids closed (Fig 4).
Fig 5: Lambs with tetanus show hind leg stiffness
progressing to lateral recumbency, seizure activity and death -
such losses are unacceptable.
Lambs show hind leg stiffness and
difficulty walking leading to lateral recumbency, seizure activity
(Fig 5) progressing to opisthotonus, and death from respiratory
haemolytica (previously termed P. haemolytica biotype
A, but now more correctly called Mannheimia haemolytica)
is of considerable economic importance to the sheep industry
causing septicaemia in young lambs, pneumonia in older sheep and
mastitis in ewes. Bibersteinia trehalosi
(previously termed Pasteurella trehalosi) causes
septicaemia in 4 to 10 month old lambs. Systemic pasteurellosis
caused by B. trehalosi is the most common cause of sudden
death in lambs in the UK between August and December (Fig 6).
Fig 6: Systemic
pasteurellosis is the most common cause of sudden death in lambs in
the UK between August and December.
Prevention is best attempted
using vaccines incorporating iron-regulated proteins. Since these
iron-regulated proteins are antigenically similar they confer cross
protection against other serotypes. Breeding ewes require a primary
course of two injections four to six weeks apart followed by an
annual booster four to six weeks before lambing. The pasteurella
vaccine is combined with clostridial disease vaccines. However,
this pasteurella vaccination regimen of the dam only provides
passive immunity to the lambs for up to five weeks.
Lambs can be protected by two doses
of vaccine administered from 10 day-old as colostral antibody does
not interfere with the development of active immunity.
Alternatively, lambs can be protected against systemic
pasteurellosis by two doses of vaccine given four weeks apart with
the second injection two weeks before weaning/sale but this has
rarely been undertaken in most store lambs presented at
Fig 7: Farmers must not
forget the large number of highly efficacious vaccines without
which intensive sheep farming would prove very difficult
Farmers are advised to vaccinate their ewes against the
clostridial diseases four weeks before lambing. It is advisable to
vaccinate the flock as two separate groups with the later lambing
ewes vaccinated one week to 10 days later than those ewes lambing
in the first week. The ewes must be dry when they are vaccinated
and care must be taken to ensure correct subcutaneous injection of
every ewe (Fig 7). Subcutaneous injection of ewes when they are wet
may result in contamination of the needle and abscess formation.
Patient handling of the pregnant ewes is essential during the
operation; speed is not important. Farm dogs should be kept out of
the way whenever possible to reduce stress.
Fig 8: How many lamb
losses on your farm could have been prevented by appropriate
By ensuring ewes are in good
condition at vaccination time, and receiving an appropriate level
of supplementation plentiful accumulation of protective antibodies
in the ewes' colostrum will be guaranteed at lambing time. The
importance of ensuring passive antibody transfer within the first
two hours of the lamb's life cannot be over emphasised.