The Farmers Mart Jun-Jul 2020 - Issue 69 | Page 19

• JUN/JUL 2020
LIVESTOCK 19
down through the eggs)
through an inactivated
‘killed’ vaccine given at
16-20 weeks old (individually
injected) following
initial ‘priming’ with live
vaccines.
• Live ‘attenuated’ vaccines
are described as three different
‘hotness’ levels (mild,
intermediate and intermediate
plus), this essentially
just indicates the ability
of the vaccine to ‘break
through’ the MDA levels and
achieve a response from
the bird itself. Care should
be taken as the ‘hotter’
these vaccines are the more
likely they are to replicate,
damage the Bursa and
cause immunosuppression.
In most flocks, a well-timed
intermediate vaccine works
well.
• Vaccine timing prediction
can be calculated using the
levels of MDA present in the
blood of day old birds using
the Deventer formula. This
will need to repeat for each
parent flock code as the
levels of MDA are variable.
It usually requires 20 birds
from each flock code/house
to be culled and blood
sampled.
• New in-ovo vaccination is
a technique for vaccinating
birds before hatching and
will mean that in theory
there will be a more uniform
uptake of vaccine. It is
already well established in
hatcheries over in Europe.
• There are other novel
vaccines available, these
include;
• Live viral vector vaccination
using a different
attenuated virus (such as
HVT) either by the in ovo
or subcutaneous route
at 1 day old. The vector
virus will have Gumboro
viral antigens presented
on its surface but will not
cause the disease. It also
allows us to bypass the
MDAs that are obstacles
in normal live attenuated
viral vaccination.
• Immune complex vaccines
could be used in
ovo or by subcutaneous
vaccination in hatchery
at day old. They bypass
the MDA’s and have
been shown to provide
better immunity against
Gumboro than conventional
live vaccination.
• Testing for Gumboro virus
in the flock should be done
regularly to check for both
vaccine and field strains;
• This can be done by taking
bursal samples at 28 days
old to PCR test.
• Blood samples can be
analysed for antibodies
using an antibody ELISA
test. This will give an
indication of exposure to
field and vaccine strains of
Gumboro virus.
A close association with your
veterinary practice will be key in
monitoring the health status of
your flock. They will also assist
you in assessing your current
vaccination protocols including
technique, timing and the choice
of vaccine to use.
Authors Dr Elizabeth Ford BVetMed
MRCVS, PHS vets Sutton Bonington
Branch and David Parsons B.Vet.
Med., MSc, CertPMP, NSch, MRCVS-
PHS vets Hereford branch.