There is still some concern about
worm infestations in sheep and horses that have become resistant to all available
treatments and the thought is that we could do more to stop the problem
developing. It has long been known there are resistant strains of strongyl worms. The problem was first reported in
Correct Dosing
Important things to remember to
stop the development of resistant worms are to make sure that the sheep are
given the correct dose. Weight them if you can and calculate the dose for the
heaviest animals in the group. When worms are in contact with a drug that is
not concentrated enough to kill them resistance is likely to develop.
There are several different worms
that cause problems for sheep. So far the ones that have become resistant are
the ones like Haemonchus contortus
that cause weight loss late in the summer and autumn. There is less concern
about the ways in which you control worms in the spring and early summer as
parasites like Nematodirus battus
are less prone to developing resistance.
When the animals are drenched all
of the susceptible worms perish, but a small number of resistant worms survive
and will start to build up on the pastures. Within the host animal there is
competition between the various worm species. It has been found that in the
summer and autumn it is better to turn treated animals back onto contaminated
pasture so that they will start to take in a board spectrum of worms so that
the resistant ones will be edged out by competition from others from the
pasture.
If you think you’re tried and
trusted worming regime is starting to be less effective the way to monitor the
situation is to get ten or twelve animals into a clean pen with a solid floor
one week after they have been drenched. Collect the dropping from the floor
into one bag so that we can check how many worms are present. If the wormer is
not reducing the egg count then a different class of drug should be used and
more samples taken. With the way that sheep move around I suspect that if we
were to look hard enough we would find that this is a problem to some degree on
many farms. The trick is to limit the build up of resistant worms in the summer
and let them fight it out with the ones that you are more able to control.
There is more about this problem on the Defra Website.
Worming Cattle
In the past five years or so there
has been a considerable change in the way that we tackle worms in cattle. There
has been a noticeable move away from struggling with drenches to pour on
products, which cover a broader range of parasites and are much easier to
administer. You might still have to drench your cattle if you have problems
with fluke.
Many high yielding Dairy Cows are
wormed every year and it is quite noticeable how this improves their milk yield
and stops them suffering the effects of mange and lice in the winter. Sheep do
share some of the gut worms that affect cattle, but fortunately there does not
seem to be any signs that there is resistance to any of the wormers that are
given to cattle.
Worming Horses
There have been reported cases of
resistant strongyl worms in horses. Brood mares are a
particular problem here as they are liable to move onto contaminated fields at
a stud farm at the time when they are most susceptible to developing worm
infections. Again all of the different wormers fall into just three chemical
groups. Many horse owners will be concerned about Bots and use an Ivomectin type product early in the winter and a double
dose of Strongid P at some stage during the year to
combat tapeworms.
These are strategies that are
liable to limit the development of resistant worms. Some horse owners with restricted
grazing tend to pick up and compost any dropping which further restricts the
contamination of their fields. In many ways the problem is much easier to
control in horses as long as regular samples are taken to monitor the
effectiveness of the dosing regime.
Neurology Project
We are participating in a project
at the moment on behalf of the National Disease Information Service to do a
series of simple neurological tests on cows destined for the Casualty Slaughter
Scheme. Part of the reason behind this is to determine whether Vets in Practice
can gather information useful to researchers working on various conditions in
cattle.
Sheep Scab or Louse Infestations
This is the time of the year when
sheep start to rub. Now that fewer animals are dipped it can be difficult in
the early stages to determine if the rubbing is caused by sheep scab or by
biting lice. Neither of these parasites is easy to live with, with scab you do
have the option of injecting instead of dipping. Sometimes if you are selling
fat lambs you might be able to put up with a low grade louse infection to allow
the sale of some of the least affected animals without having to deal with drug
residues.
Free Testing
From now until the end of February
the Veterinary Laboratories Agency will look at wool samples free of charge to
determine whether there are any scab mites or lice
present. The best samples to bring are plucked wool from the edge of the
lesions or from any new lesions, not necessarily where the skin is most
damages. If you can sample three or four different animals
and put the wool in separated bags. We have already had a case of sheep
scab this winter, involving just one animal, without a lot of rubbing. Take
time to watch the ewes in the field to see if there have been any changes in
their behavior. It is quite possible to effectively treat scab before it has a
chance to get established as long as you catch it early enough.
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