AUTUMN 2015 ISSUE
EQUINE MATTERS
6
The important factors are:
Pasture Management
Not overstocking your fields (1-1.5 acres
per horse) and poo-picking once or
preferably twice a week will prevent larvae
spreading on to your pasture. This is more
effective than any wormer. Muck should be
composted well away from grazing areas.
It is also useful if you can rotate your
grazing, rest paddocks for at least 3
months and cross graze with other species.
Harrowing pasture is only useful in dry, hot
conditions as eggs and larvae on pasture
survive wet, cold conditions.
Worm Egg Counts (WEC)
All you need to do is collect a fresh ‘ball’
of dropping (about 10g) in a clearly
labelled plastic bag or pot and drop it off
on the same day at your local XLVets
practice. They will be able to perform a
faecal worm egg count (WEC).
Horses
with persistently low or zero WECs do not
need to be tested again for six months.
Horses with high WECs should be treated
and retested in approximately 3 months
(depending on worming product used).
If your horse has consecutive very high
burden WECs they should be tested again
post-worming to check for resistance (eggs
per gram (epg).
Faecal worm egg counts are not a reliable
test for identifying a tapeworm burden.
Tapeworms are significantly associated
with spasmodic colic and ileal (part of the
small intestine) impaction. There is a blood
test that can be done as a one off test to
check for tapeworms and more recently a
saliva test has come on the market. These
tests are limited as they cannot discriminate
between non-infected horses and those with
low levels of infection and interpretation is
complicated if horses have been treated for
tapeworm in the last 4-6 months.
Praziquantel and double dose pyrantel are
both effective in treating tapeworm
burdens. WECs are also unable to pick
up larval cyathostomin (small redworm)
burdens in the gut wall. Large numbers of
larvae can accumulate as most wormers
are ineffective at killing these immature
worms. Large numbers of larvae emerging
from the gut wall can cause severe
inflammation, diarrhoea and even death.
This condition is called larval
cyathostominosis. Moxidectin is the only
wormer effective against encysted larvae to
which resistance has not yet developed
therefore an annual treatment with this
wormer is recommended in winter.
Worm egg counts >200 epg should be
treated with an appropriate wormer.
Using wormers effectively
If your horse's WEC comes back positive,
treat with either ivermectin or pyrantel. It is
important you accurately assess your horse’s
weight (with the use of a weigh band or
scales) and dose accordingly. If you are
using oral syringes, set to the correct dose
then remove the syringe cap. Stand at the
side of your horse, in front of their shoulder,
and open your horse’s mouth. Guide the
syringe into the corner of their mouth and aim
it towards the back of the tongue before
dispensing the wormer (do not dispense the
wormer at the corner or front of the mouth
where the horse may just spit it out). It may
be necessary to raise the horse’s head briefly
to ensure the wormer is swallowed. You can
mix wormers into part of your horse’s feed,
adding something tasty to tempt the horse.
Once the wormer has been eaten, the
remaining ration can then be fed.
As moxidectin is the only product still
effective at killing encysted cyathostomin
larvae, it should be reserved for this
use only.
Widespread resistance to benzimidazoles
now exists and therefore their use should be
restricted to premises where its efficacy has
been proven using faecal egg count
reduction tests.
Any new horses brought onto your yard
should be wormed with Equest Pramox to
target any encysted small redworm larvae
and tapeworm burdens. They should have
no access to grazing for 72 hours after
treatment to prevent contamination of pasture.
Worming of foals
Foals are particularly sensitive to worms as
they have no natural immunity and will start
to pick up eggs from the environment and
the mare’s milk from the day they are born.
This can result in infection from 2 weeks
of age.
To protect your foal it needs to be wormed;
Pyrantel, Fenbendazole and Ivermectin are
all safe to use in foals and should be
alternated to reduce the possibility of
resistance developing. Unless the infection
pressure is very high (for example on large
stud yards), it is advisable to start with the
first wormer at approximately 8 weeks
and repeat treatment every 6-12 weeks
(depending on product used and pasture
management). At that point the foal can be
treated like the other (adult) horses on the
yard. In foals younger than 4 months
Moxidectin should NOT be used as it
can cause serious side effects.
Pregnant mares should be treated 2 -3
months prior to foaling, to reduce their
worm burden and pasture contamination.
Interval dosing
In a busy livery yard or riding school
performing faecal egg counts may not be
possible, and instead interval dosing may be
the only option. This involves using
wormers at set intervals throughout the year.
In spring use an appropriate wormer for
roundworms and tapeworm; throughout
the summer grazing season treat for routine
worms at the appropriate frequency for the
product used; in the autumn treat for
tapeworm and in the winter use your
larvicidal dose of wormer for the encysted
redworm. Always remember to treat all
horses on the same day with the same
product and record what you have used. The
main disadvantage of this strategy is horses
being dosed unnecessarily which encourages
the development of resistance.
If this article has just opened up a can of
worms and left you confused contact your
local XLVet practice and they will be happy
to advise. Every situation is different and
programmes can be tailored to suit your
particular need.
Chemical Family
Active Ingredient
Benzimidazole
Fenbendazole
Benzimidazole
Mebendazole
Macrocyclic Lactones Ivermectin
Macrocyclic Lactones Moxidectin
Pyrimidine
Pyrantel
Quinolone derivative Praziquantel
Combination
Ivermectin and
Praziquantel
Combination
Moxidectin and
Praziquantel
EQU INE WORMING