Volume 22 • Issue 05 • 2018
R - 13 Sep 2013
As a practice we have discussed this disease and
its implications and our opinions may be similar
or completely different. We have an extremely
high prevalence of this disease in and amongst
our dairy herds. The number of post mortems
that we do that point to EBL as the primary cause
of death are just a fraction of the clinical cases
that we see with generalised lymphadenopathy,
which in turn are just a fraction of the number
of subclinical cases grazing and milking (quite
happily/unhappily).
Ultimately the number of clinical cases and PM’s
of EBL that I see hardly compare to those of
sub-acute rumen acidosis, Redwater, Clostridial
infections, Listeria, Lumpy Skin, etc. etc. I
definitely feel it is a disease to be aware of and
understand, but how much does EBL affect overall
herd fertility/performance/mastitis/costs? It is
hard to say and I think there are greater problems
affecting dairy herds than this disease. Besides,
with no vaccination available and with the disease
being transmitted through vaccination needles/
rectal gloves/infected fomites and possibly even
biting midges and flies, how can one practically
control EBL?
With high prevalence and transmission how can
a slaughter out policy work and if most farms
are positive for the disease is it worthwhile
testing and buying only EBL negative animals?
With regards to the losses that Jan du Preez talks
about, are these not tied in with other causes
either primary or secondary (Hypocalcaemias /
Keto-acidosis / metritis). This is a chronic disease
and for one herd to lose 30 animals within a short
space of time doesn’t sound like an EBL epidemic.
WS - 15 Sep 2013
I think the most pressing question from farmers
is to what extent in monetary terms does the
EBL erode the business. That is the outstanding
answer the veterinary profession in SA owes its
farmer clients. Once we know what it costs, we
can decide how much money we can throw at
the disease...If it costs the farmer R10, then it is
futile to spend R100 in control measures. Yes,
I know it's more complicated than that! I think
there may be overseas surveys that could shed
light on this, so, a good literature search would
be appropriate. The most appropriate way for a
local, South-African study, with all the statistics
& production economics etc. included, would
be to compare within the same herd, in several
herds, in several different systems, the difference
in production and reproduction parameters of
affected (sero-positive?, carriers) versus those
that are NEGATIVE/ clean over an extended
period of time, say at least for one year...where
there is a solidly, well-understood and managed
electronic record system in place.
RM - 8 Nov 2014
Yes, there is a problem out there. But, we have
more serious issues to worry about. We cannot
even control CA in SA. EBL is not economically
important in mega herds as they seldom have a
high proportion of cows that stay for long enough
to become clinically sick with lymphomas. Let’s
rather get the basics right, and once we have
ticked that box, we can saddle new projects.
PT - 15 Sep 2013
I agree the issue of impact of the disease is one
of the most important to address. Some studies
on this have been done overseas, as mentioned
by Will Gratwick recently. Currently we have two
postgraduate students, one of whom is Will, who
are starting with a study, or rather two small
combined studies, to estimate the herd-level
prevalence of EBL in commercial dairy herds in
SA and to identify herd-level risk factors for BLV
infection. This is being done in collaboration with
the MPO (Jan du Preez) and we have applied to
Milk SA for funding to randomly sample and test
a large number of herds across the country using
a bulk tank ELISA. Depending on the funding
received we will extend the testing to individual
animals within herds. We believe the first step
towards addressing the problem is to know its
extent and distribution, hence the prevalence
survey. This will then help us to identify suitable
farms for further studies, which may be along
the lines of what Willem suggests, depending on
the availability of a good student and sufficient
sponsorship. This is also advance warning that
we may possibly be calling on Ruralvet colleagues
at some stage to help with sample and/or other
data collection.
CONCLUSION
MvdL - 20 Sep 2013
Some information & an approach that might also
be shared with a client.
Virus induced. No treatment. No vaccination.
The majority of cows are asymptomatic. Less
than 5% of infected animals develop clinical
signs & die. About 30% of infected animals may
show decreased milk production & altered milk
components of up to 3%. It is almost exclusively
transmitted by transferring infected blood or
blood products from animal to animal through
objects (horizontal transmission by needles,
palpation sleeves, dehorners, etc.). At a low
prevalence it is not considered a significant
disease/threat. At a high prevalence, & once the
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