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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