January Newsletter 2023

Johnes and Neospora .... a 21st century
solution to loss of herd genetics.
A diagnosis of Johnes or Neospora in a
cow or heifer can be devastating as it
often means the end of her breeding
career. Tyndale Vets have been boarding
these animals and producing disease free
embryos by IVF for several years with great
success.
In this article we look at practical control measures for these
important diseases and suggest an option for infected animals.
Johnes disease
This is probably the most difficult disease of cattle to control.
Animals are infected many years before they test positive
and indeed can be infectious to other animals whilst still
themselves testing negative.
The cause is a hardy bacterium called Mycobacterium
avium subsp. Paratuberculosis or thankfully MAP for short.
The vast majority of affected animals became infected under
6 months of age. Any test for the disease at this stage will
likely be negative. The bacteria lodge themselves in the small
intestine and take up permanent residence within the cells of
the calf. At this stage the animal is clinically well but at some
time, often years later, the bacteria begin to shed themselves
in the faeces allowing infection of other young animals. The
infected cow will also produce antibodies that will yield a
positive Johnes blood test result. Shedding and becoming
antibody test positive unfortunately do not occur at the same
time meaning that in an infected herd you do not necessarily
know which animals are shedding and which are not. However,
removing antibody positive animals significantly reduces the
amount of MAP in the environment, reducing the likelihood of
new infections.
To make matters worse, the stress of calving and lactation
make progression of the disease to the shedding stage more
likely. Calving also now means that there are multiple disease
susceptible calves around making the whole situation worse.
Many infected dams will infect their own calf and infection
becomes almost a certainty once the dam is antibody positive.
Remember though that this calf will be infected but will
remain antibody negative for several years. Antibody positive
dams will likely be shedding much more than antibody
negative ones and they become a risk to calves other than
their own, especially when calving indoors.
Practical control measures in a suckler herd are more limited
than in dairy herds as the calves will nearly always be running
with their dams and often a bull as well. Several control
schemes are available and a good place to start looking at
these is the CHECS website (www.CHECS.co.uk) which is an
industry led, not for profit organisation for cattle disease
control.
Fundamentally, all schemes work towards the same end
goal. They identify the positive animals, enabling them to be
removed from the portion of the herd with calves present.
Retaining daughters from a positive animal for breeding
purposes simply keeps, and indeed magnifies, the problem
within the herd for future years.
The good news is that infected cows and heifers produce
clean embryos from both conventional and IVF embryo
production processes. Whilst these animals are blood positive
but clinically well, success in embryo production is within the
normal range. Sadly, once an animal is clinically unwell results
are poor.
At Tyndale Vets we have a dedicated shed for blood positive
Johnes animals. Bedding is separated for spreading onto
arable land and contact with clean stock is avoided. These
cows and heifers have been successful in producing disease
free embryos for transfer back to the herd of origin thus
maintaining valuable genetic lines that might otherwise be
lost. We can produce embryos using a variety of bulls to
increase breeding options and this can be an opportunity to
introduce new lines instead.
Neospora disease.
Neospora is the main infectious cause of loss of pregnancy in
cattle, often between 5 and 7 months gestation. Remarkably
it was only discovered as recently as the 1980s. The cause
is a protozoan that is closely related to Toxoplasma, a
similar disease of sheep. Both parasites have 2 hosts in their
lifecycles. In the case of Neospora it has to go from cow to
dog and back again. Cows rarely infect other cows however
dogs can infect other dogs. The only exception to this is via the
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No bull works harder for the farmer, the plate and the planet