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September Newsletter 2003 |
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Summer Problems August has it seems been a good
time for farm stock and we have spent more of our time testing cattle for
tuberculosis and sheep for maedi visna and scrapie than we have dealing
with outbreaks of disease. There have been several outbreaks of pneumonia in
calves and it has been quite noticeable that dairy cows are coughing on some
of the farms that we visit as they battle with migrating lungworm larvae.
Several farms are still having problems with high cell counts. At this time
of the year we see a drop in the number of cases of environmental mastitis as
teats tend to be clean and dry. When that goes into the background it is Strept uberus and Staph aureus that
is revealed on the samples that we culture. Often it can be difficult to
detect the quarter that the infection is in, but if you are able to take milk
samples it will be evident in a plastic container that the milk is of poor
quality and likely to grow some significant organisms. Some of the samples
lately have had a very restricted sensitivity pattern leaving only one or
possibly two drugs that they are likely to respond to. It is important to
identify these cows and treat them intensively to halt the spread of infection
within the herd. Calf Pneumonia Often when we are treating
respiratory infections in calves we cannot be entirely sure what the likely
cause is. It is sometimes only the age of the animals and the presenting
signs that point towards the most likely dominant organism involved. Now and
again in a severe outbreak if there are any losses there will be a chance to
get samples from a postmortem examination. Sometimes this can be frustrating
because of the time it takes for tissues to be cultured or examined under the
microscope. It may be several weeks before all of the tests are completed and
the disease may be long gone before a definitive diagnosis is made. This is
always the case when Mycoplasma bovis is
present we know that it will be two or three weeks before any significant
results will turn up. Mycoplasmas cause severe
pneumonias as they cause a lot of fluid to accumulate in the lungs and the
airways will get blocked. Mycoplasma infections are
difficult to treat because even the drugs that are
supposed to have some activity against them need to be given for a prolonged
period and too much damage has often been done before the treatment is
started. Ewes with eye infections Also in August we seem to have
had a large number of eyes to treat for various reasons. Sheep sometimes get
an eye infection called Infectious Keratoconjunctivitis.
It will occur also around lambing time when the ewes are fed from a trough
and knock their heads as they feed. Outbreaks that occur in the summer when
it is dry and dusty seem to take longer to respond to treatments. It might be
that the bright sunlight aggravates the infection and makes things worse.
Mild cases may not be noticed as one or both eyes may be watery for two to
three days before the inflammation subsides. In severe cases the eyes will be
inflamed and have a white film over them, if both eyes are affected they will
not be able to see very well and may lose contact with the rest of the flock.
Early cases will often respond to one dose of an antibiotic eye ointment. If
the disease has developed and especially if both eyes are involved it is
often better to inject antibiotics as well to stop the infection penetrating
deep into the eye. Sometimes on sunny days it is necessary to house
individuals that are worst affected as they do not seem to be able to cope
with intense sunlight. Calves with eye infections New Forest Disease is the bovine
equivalent of Infectious Ketatoconjunctivitis
although it is caused by a different organism Moraxella bovis. This bacterial infection is
more severe in the way that it will cause ulceration on the surface of the
eye. These can develop rapidly and may cause a permanent scar to form if the
infection is not treated at the earliest opportunity. Modern eye ointment are
very good in the way that they have been formulated to be absorbed onto the
surface of the eye and remain active for at least twenty four hours. Where
the infection is well established we sometimes have to give antibiotic
injections under the membranes of the eye so that they slowly release the
antibiotic close to the infection. This will usually give a better result and
a swifter recovery. Listeria The other eye infection that
cattle get is caused by a bacterial infection that comes from the soil. Listeria acts in a different way when it infects the
surface of the eye. It does not seem to cause too much damage on the surface
but rapidly penetrates to the deep structures infecting the whole of the
front part of the eye. Eyes do not cope well with inflammation and it is
often this rather than the infection itself that is the source of the
discomfort. Antibiotics do help to control the infection, but because the
infection is deep within the eye a better response is seen if anti
inflammatory drugs are given at the same time. Sometimes the eye is affected
to such an extent that there will be hemorrhage within the eye and the whole
structure will go white. It is surprising that these eyes will eventually
heal with seemingly little detriment to vision. Cataracts Earlier today I found myself
looking into the eyes of a yearling beef heifer who
was thought to have had a problem with her eyes since she was a calf. This
animal was housed and was difficult to catch as she was most confused when
separated from her companions. Closer examination revealed that her eyes were
cloudy and that she was keeping both of them as wide open as she could to
make the best use of her restricted vision. It is not uncommon for calves to
be born with cataracts. One of the causes is if the mother of this calf contracted
the Bovine Viral Diarrhea Virus when she was pregnant and the eyes were
damaged before birth. Sometimes there can be other causes. This heifer was
obviously able to cope with her disability and had grown at the same rate as
her companions. Cattle are able to make better use of their other senses when
they cannot see properly and there is no reason why she will not be able to
fatten as well as the others in the shed. Acorn Poisoning Some of the worst years that we
have had for acorn poisoning have followed a dry summer so there is a risk to
cattle in the coming two months. Acorns are bitter and most cows will not
touch them although certain individuals will actively search for them often
with fatal consequences. If there is an abundant crop of acorns this year do try to organize the grazing so that cattle do
not have access to them. Spreading slurry under the trees may be enough to
deter stock from taking an interest in the acorns as the poisoning is
difficult to treat once it occurs. |
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