C4-Lancaster Farming, Saturday, January 23, 1993
\
Pennsylvania
PRV HEADLINES /
A bi-weekly communication from S
PA Pseudorabies Committee and Penn State Extension v.
to alert you to developments in PRV and its control \
PSEUDORABIES
VACCINATION
QUESTIONS AND
ANSWERS
Dr. Amy J. Nesselrodt
Dr. Paul M. Pitcher
USDA Veterinarians
In the last edition of Pennsylva
nia PRV Headlines, issues sur
rounding pseudorabies vaccina
tion were discussed.
This week, commonly asked
questions will be answered.
More than 200 of Pennsylvani
a’s swine herds are being vacci
nated against pseudorabies. There
are many swine herds that are not
vaccinating but which should
because they are located near other
herds that are infected with
pseudorabies.
Will vaccination prevent
pseudorabies infection? Not
always. Vaccination does not pro
vide perfect protection against
infection.
Why, then, should I vaccinate?
Properly administered vaccination
is very effective at reducing or pre
venting signs of pseudorabies in a
swine herd.
These signs were discussed in
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an earlier article in this series
(October 24, 1992 issue of Lan
caster Farming). The signs of
pseudorabies can be obvious and
costly in an acute outbreak. Often,
however, the signs are not as obvi
ous. In the grow/finish herd, losses
because of slower and less effi
cient growth may be hard to
observe unless careful measure
ments of feed consumption and
days to market are made.
Even though these less obvious
signs are harder to observe, they
are very costly. Also, there is evi
dence that pseudorabies infection
makes a herd more prone to other,
more devastating diseases such as
rhinitis and pneumonia.
Properly vaccinated pigs have
greater resistance to infection with
pseudorabies than unvaccinated
pigs. This means that it takes a lar
ger amount of virus to infect a vac
cinated pig. Vaccination can allow
the swine producer to avoid being
quarantined for pseudorabies,
because this resistance will help
prevent infection of the herd if the
pigs are exposed to pseudorabies.
Exposure to infective doses of
pseudorabies virus is much more
likely during the cool months, so it
is important to boost herd protec
tion now.
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If they do become infected,
properly vaccinated pigs shed
much less virus than unvaccinatcd
pigs. This prevents new infections
and controls the spread of pseudo
rabies on the farm and to neighbor
ing farms.
Is it cost-effective to vaccinate
against pseudorabies? Yes. Field
studies in Illinois and Minnesota
have indicated that conversion of
feed to pork can be improved by 6
to 10 percent when pseudorabies
virus circulation is prevented by
vaccination of fat hogs. Daily gain
is also improved, so pigs reach
market weight sooner. The Minne
sota study found that one dose of
vaccine given to fat hogs relumed
an additional $l3 gross profit per
Pig!
The incidence of diseases such
as rhinitis and pneumonia can be
reduced by pseudorabies vaccina
tion. A producer in Illinois esti
mated that pseudorabics vaccina
tion returned S 3 to $4 in improved
performance for each $1 spent on
vaccine.
Do I need to vaccinate the entire
herd, or can I just vaccinate my
breeding herd? Experience has
shown that it is difficult to prevent
or eliminate the disease in a breed
ing herd if virus is circulating on a
nearby finish floor. Have fat hogs
blood-tested for pseudorabies to
determine if they have been circu
lating virus.
Vaccination is only one of sev
eral tools effective at eliminating
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pseudorabies from a herd. Several
top managers in Lancaster County
have apparently eliminated
pseudorabies from their finish
floors by using segregation and
biosecurity techniques (see the
Pennsylvania PRV Headlines col
umn in the December 19, 1992
issue of Lancaster Farming).
Their management skills ensure a
stress-free environment for their
hogs, which helps to prevent
pseudorabies virus circulation.
I have heard different recom
mendations of how often to vacci
nate for pseudorabies. What is the
best advice? In the past, we
advised vaccinating the breeding
herd against pseudorabies twice a
year or prior to each farrowing.
However, experience has shown
that the protection given by vacci-
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nation may be gone in less than six
months, making the herd prone to
infection before the next booster is
given. Ideally, the breeding herd
should be vaccinated every three
months, or four times per year. In
many herds, it appears that vacci
nating every four months or three
times per year provides continuous
protection against pseudorabics
infection.
A word of caution: If the herd is
severely challenged at a time when
protection is at a low ebb, vacci
nating every four months may not
be adequate to prevent infection of
the herd.
Try to time pseudorabies vacci
nation to anticipate periods when
severe challenge is likely (late fall,
winter, and early spring).
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