Equine Worms are parasites that live in the digestive system of your
horse. Most types of worm do little damage to the horse but some
of the more dangerous ones can cause colic and death.
Most gut worms that affect horses live both inside the horse
and out on the pasture. Inside the guts they live on body fluids
and the lining of the guts causing a lot of damage. Eggs are laid
inside the horse and pass out in the droppings where they hatch on
the pasture ready to recontaminate another horse when they are
eaten along with the grass. Worms must therefore be controlled by
reducing contamination of droppings on the pasture and by a normal
regular worming programme.
Your horse may get serious worm problems because of grazing the
same pasture each day. In the wild horses will graze a much wider
area and the level of worm contamination does not build up as high
as on your pasture at home. In addition low levels of worm
infestation in the wild allow horses to develop a better and
stronger immune system against the worms.
The most dangerous worms are the redworms such as Strongylus
Vulgaris. Such worms are eaten by your horse and then bury through
the wall of the guts so that they can penetrate blood vessels
nearby. Here they grow doing much damage before burying back into
the guts so that they can live as adults, laying eggs and feeding
off the gut wall. These worms damage your horse by interfering
with the blood supply to the guts when they are living in the
blood vessels and by damaging the lining of the bowels when they
feed in the large intestines.
Encysted larvae: One danger with worms is there ability to ly dormant in the lining of the bowel over long periods. If not
treated properly large numbers of such larvae can suddenly hatch
out in the spring when conditions are right for them to live on
the pasture. Sudden hatching of all these dormant larvae can cause
serious problems but treatment with the right wormer at the right
time of year will avoid the problem.
Types of worm that do not cause a lot of damage are Tapeworms
and Bots. These should still be treated for since they can cause
blockage and physical obstruction and low grade soreness.
Treatment for Equine Worms
We will not discuss the various worming programs here but the
broad principles behind them.
The idea behind worming programs is to eliminate all worms in
the horse’s digestive system. Some might say that this is not a
good idea as the horse will not develop any ability to build up
its immune system. In reality there are likely to always be a few
worms around on most pasture.
The best way of checking whether your horse has a problem is by
doing egg counts in the droppings. Such egg counts will however
not measure how many immature worms have been eaten recently and
are living in the body. Counts will also not show up how many
encysted larvae are present. There is no way of knowing how many
immature worms are present or whether encysted larvae are a
problem – in such cases you have to rely on knowledge of whether
there have been problems before and worm accordingly.
It is possible to get away with limited use of worming agents
if you have excellent control of worms on the pasture by picking
up droppings regularly etc. Such management practices should be
carried out in conjunction with your local vet and regular worm
egg count checks. This is however dangerous practice and can lead
to serious problems. Remember that any new horse introduced into
your system may introduce new worms.
In the wild horses may eat plants which help control the worms
in their bowels. Currently there are a few herbal wormers
available. Owners should be aware that none of these herbal
wormers have been scientifically evaluated to show how effective
they are and it is dangerous to rely on them instead of chemical
wormers. Herbal wormers are best used as part of a worm control
program advised by your veterinary surgeon. Many plants do help to
reduce worm numbers however and feeding plants like garlic can be
very useful in helping limit the activity of worms.
Dangers of wormers:
Wormers are powerful chemicals which have side effects. Used
very 6 weeks over a number of years these side effects can damage
some horses. Read through the warnings on the wormers you are
using and discuss with your vet what steps are best to take to
limit side effects. Some feed supplements can be useful in this
regard.
Changing wormers:
Worms are clever little animals and can develop resistance to
chemical wormers designed to kill them off (just like bacteria
become resistant to antibiotics). Regularly changing the type of
wormer you use can help a lot and you should seek advice from your
vet as to what is the best program you can use.
Pasture Management Practices:
- Removing droppings twice weekly (before eggs hatch out)
- Divide paddocks into areas of long soar grass where horses
pass their droppings and close-cropped areas for grazing.
- Mixed grazing with cattle and sheep can help a little but is
not that effective at reducing worm numbers
Harrowing during dry spells can speed up the drying out of
droppings so that larvae die out more quickly. Do not do it when
pasture is damp.
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