William Barr MRCVS
William Lockhart MRCVS |
(017683) 71359 |
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| We aim to provide a friendly, helpful
and affordable veterinary service to all our clients. |
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Worms
in Horses and Ponies
 Back
to Horse Owner's Factsheets Index |
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| Every
horse owner has heard about the danger of worms
but without some knowledge it is hard to understand
the full impact of a worm infestation (or burden).
Intestinal worms can seriously damage your horse
and in some circumstances can kill it - implementing
an effective worming programme is one the greatest
responsibilities of a horse owner. |
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| What
are worms? |
| Worms
are parasites which means that they live within,
and take nourishment from the host (your horse).
The four most common types of internal
parasites are Strongyles, Ascarids, tapeworms
and Bots.
| Parasite |
Stage I |
Stage II |
Stage III |
| Strongyles
(blood or red worms) and Ascarids (roundworms) |
Eggs are passed in
the horse's faeces and contaminate grass,
hay or water. The grazing horse eats
the eggs or newly hatched larvae in
the contaminated feed. |
Larvae burrow through
the gut wall and migrate through the
internal organs for several months causing
irritation and damage, which can result
in attacks of colic. They then return
to the gut where they mature. |
Adult worms live in
the gut where the females can produce
thousands of eggs per day. |
| Tapeworms |
Segments containing
eggs are passed in the faeces. The eggs
contaminate hay and are eaten by an
intermediate host - the forage mite. |
Larvae develop inside
the mites which are eaten by horses
feeding on contaminated hay. The larvae
develop into adult worms in the horse's
gut. |
Adults live in the
ileo-caecal junction of the gut where
they attach to the gut wall by hooks.
They cause inflammation which together
with decreased gut motility leads to
an increased risk of gut obstruction
or even rupture. |
| Bots or warbles |
Adult flies lay yellow-coloured eggs
on the chest, forelegs, throat and nose
of the horse. |
When the horse grooms, the larvae
hatch and enter the mouth. They migrate
to the stomach and attach to the stomach
lining causing irritation, digestive
problems and gut obstruction. After
8-10 months, they are passed in the
faeces. They burrow into the ground
to pupate. |
Bot or warble flies emerge from the
ground. |
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| Blood
testing |
It
is possible for a horse to have a heavy larval
infestation but have very low faecal egg counts.
This is because the larval stages do not produce
eggs. A blood test is the only way to detect
whether a horse is infected with larvae. It
measures certain chemicals in the blood produced
by inflammatory responses to the migration
of the larvae.
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| How
does my horse get worms? |
Your
horse will get worms if it is turned out with
horses or donkeys that have worms, because
the pasture will be contaminated with eggs
and larvae. Your horse will eat these as it
grazes. Pastures can remain contaminated for
a considerable time after horses are removed
so even if your horse is turned out alone,
it could still get worms from the pasture
or contaminated hay. Bots can affect any horse.
Similarly, if your horse has worms, it can
infect other horses grazing in the same field.
Horses most at risk from heavy worm infestations
are young or older animals or those on multi-horse
premises, eg livery yards with grazing paddocks.
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| What
can I do about worms? |
Effective
parasite control is achieved by three steps:
pasture management, faecal egg count monitoring
and worming treatments. Your secret weapon
in the attack against internal parasites is
your vet. He/she can advise you on the most
effective programme for your horse.
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| 1.
Pasture management |
| The
aim of this is to break the cycle of infection
by removing the infective eggs and larvae
from the pasture.
Removal of faeces
The most effective method is to remove
and dispose of faeces from the pasture every
day which is obviously time consuming. If
you cannot achieve this daily, removing
the faeces on a regular basis (at least
twice a week) is still effective in reducing
the numbers of larvae on pasture. Mowing
and harrowing the pasture helps to reduce
larvae numbers by breaking up faeces and
exposing the larvae to the elements and
to predators.
Pasture rotation
Pasture rotation can also be an effective
way of reducing the number of larvae on
the grass. However, larvae are very resistant
and can survive for long periods (many months)
on pasture. The pasture should be rested
for at least 6 months to successfully reduce
the numbers of larvae. Allowing other livestock,
such as sheep, cattle and goats, to graze
on the pasture can help to break the lifecycles
of the equine worms.
It is essential to worm all horses 48 hours
before they are moved on to fresh, rested
paddock, preferably with the same wormer,
to prevent them contaminating it immediately
with worms they are already carrying.
Other important steps in pasture management
include:
- Keeping the number of horses per acre
to a minimum to reduce the amount of faecal
contamination.
- Turning out horses of similar age together
to reduce exposure to certain parasites
and to increase the effectiveness of your
worming programme.
- Supplying hay or grain in a rack rather
than feeding from the ground where it
could become contaminated.
- Regular grooming - if you spot bot eggs
take care to remove them completely.
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| 3.
Wormers |
Dosing
your horse with wormers has two beneficial
effects: adult worms in the intestine are
removed (some wormers also attack migrating
larvae) and the risk of re-infection is reduced
because the number of infective larvae in
the faeces is reduced.
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| My
horse hates being wormed - what should I do? |
Wormers
in the form of oral paste or gel syringes
or feed additives are very popular because
they are so convenient to use. However, some
horses find these unpalatable and spit them
out. For the wormer to be effective it is
essential that the horse swallows the full
dose based on its weight. If you find it difficult
to worm your horse in this way, your vet will
need to administer the wormer via a tube placed
directly into the stomach (nasogastric tube).
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| How
do I know what to buy? |
Worming
treatments can become ineffective over a period
of time because the parasites build up resistance
to them. To reduce the chance of this happening,
it is extremely important to rotate the worming
treatments you use. It is vital that you not
only change the brand of the worming treatment
but that you use a product with a different
'active ingredient'. Resistance to wormers
is a particular problem in some areas, particularly
the south of England. It is also important
to remember than no single wormer is effective
against all parasites and so combinations
of products should be used. Ask your vet for
advice on the rotation and combination of
treatments as this will also depend on your
location and the time of year.
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| How
regularly do I need to worm my horse? |
The
dosing frequency of worming treatments varies
according to the age of your horse, its management,
climatic conditions and season: you should
expect to worm your horse every 8-12 weeks.
Your vet is the best person to draw up the
most effective worming schedule tailored for
your horse. Some useful guidelines are:
- Keep written records detailing the
date or worming and the type of product
used for each of your horses.
- Worm all horses that share the same
grazing at the same time with the same
product.
- New arrivals should be stabled and isolated
for 48-72 hours and wormed according to
your vet's instructions.
- Mares should be wormed immediately
on return from stud and 4-6 weeks before
foaling.
- Foals can be wormed from 4-6 weeks of
age.
- Always give the correct dose based on
the weight of your horse.
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| If your horse has any health problems at all please
do not hesitate to contact us. You can be assured
that everyone at Barr and Lockhart
will do their very best to be of assistance. contact |
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This
method is extremely useful as it identifies
the type of parasite, and gives an indication
of the number of adult worms in the intestine
which, in turn, gives a measure of the degree
of pasture contamination. A fresh sample of
faeces should be placed in a clean plastic
bag and taken to your vet who will arrange
for it to be tested. The count is given as
'eggs per gram' (EPG).