Basic HTML Version
SUMMER 2014 ISSUE
LIVESTOCK MATTERS
6
BVD - THE FACTS
Theoretically, the birth of PI calves can be
prevented by vaccinating cows against BVD
before they are served. However, herd
vaccination is not a fail-safe approach.
Reasons for this include:
l
Incorrect timing of vaccination - in
particular, heifers must have finished the
primary vaccination course before they
are served.
l
Incorrect storage, or administration,
of vaccine.
l
Concurrent disease (e.g. mastitis)
means a cow may fail to respond to
the vaccine.
l
Vaccinating a PI is of no benefit - PI status
is for life, and a PI will always give birth
to a PI.
It is a sobering fact that a great number
of herds that vaccinate for BVD will have
active disease on the farm. This is not
to say that vaccination is unhelpful;
vaccination plays an important role in the
control of BVD, but it is not enough on its
own. Attempts to become BVD free through
vaccination alone will fail, unless PIs are
removed from the herd.
I vaccinate, therefore BVD can't be a problem… or can it?
A PI is an animal that is Persistently Infected
(PI) with BVD virus (BVDv). If a cow is
exposed to BVDv for the first time during
early pregnancy, she may abort.
Alternatively, the calf may continue to
develop, and although the cow will
develop immunity, the calf will not. As a
result it will be ‘persistently infected’ with
virus; a PI. These calves frequently fail
to thrive and die young, sometimes of
'mucosal disease', but until this point they
will continually shed huge amounts of virus.
BVDv suppresses the immune system of all
animals in contact, and as a result a whole
host of diseases can become much more
prevalent. In addition, PIs will maintain
infection on the farm, making control and
eradication of the disease difficult.
It is important to remember, an animal
cannot become a PI, it can only be born
a PI. PI status is for life and vaccination
will not prevent it from shedding virus. Don't
forget also, that a PI which survives until
breeding age will always give birth to a PI.
Therefore any attempt to free your
farm of BVD must involve the removal
of PIs from the herd.
PIs. What are they exactly?
PI facts
PIs continually shed huge amounts
of BVD virus
An animal cannot become a PI,
it can only be
born
a PI
Once a PI,
always
a PI - vaccination
will make no difference
A PI cow will
always
give birth
to a PI calf
Buying in cattle inevitably carries the risk
of buying in various diseases, but steps can
be taken to minimise the risks. In terms of
BVD, as highlighted above, purchasing
youngstock from a vaccinated herd is not a
fail-safe approach. You do NOT want PIs
on your farm - even if they are not obviously
stunted, they will prevent the rest of the
group from developing to their full potential.
As it is not possible to tell that an animal is
a PI just by looking at it, laboratory tests
are required - either a blood test, or a
tissue-sampling tag. The XLVets BVD Free
campaign supports the use of BVD CHECK
TAGS; uncomplicated ear tags which
harvest a sample for virus-testing, either
during the normal tagging of new-born
calves, or alternatively pre-movement.
The branded white tags provide an
easily identifiable and highly visible
prompt for calf buyers, and test results
can be checked via an online database
www.bvdcheck.co.uk
before purchase.
I don't breed cattle, therefore I can't
do anything about BVD… or can I ?
Checking the BVD status of purchased
animals shouldn't only concern youngstock
buyers - the above applies to all incoming
stock, not least for bulls. A bull will come into
contact with the entire breeding herd, so if he
is carrying infection or is a PI, the effects can
be devastating. Exposure of an adult, non-PI
bull to BVD virus can be equally problematic,
as the high temperature that may develop
as a result can cause a reduction in semen
quality for as long as two months, by which
time the breeding period may be over.
Virus may also be shed in the semen for
an extended period.
Don't let BVD hold you
back; join the XLVets BVD
Free campaign - it's time
to take control.