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W O R M I N G
SPRING 2011 ISSUE
EQUINE MATTERS
6
The XLVets Equine Forum has done a lot of
work to develop a modern approach to worm
control in the horse, in conjunction with
Professor Chris Proudman, a recognised world
authority on the subject. There are three main
areas where those of us who keep and care
for the horse need to alter our approach to
worm control;
l
Effective pasture management
l
Identifying those horses with significant
worm burdens
l
Appreciating what is an acceptable level
of worm burden in the horse
Effective Pasture Management
Pasture management alone can be a highly
effective method of worm control for the
horse. The life-cycle of worms requires eggs
passed in the faeces to contaminate the
pasture, whereby the larvae from the hatched
worm eggs can go on to re-infect that, or
other horses. Efficient removal of the faeces
from the pasture is a great method of
breaking that life-cycle. Many owners do
clear droppings from the pasture and
traditional advice has been that this should
be done twice a week. Many owners who,
for whatever reason, cannot achieve this rate
of pasture clearance may not be motivated
to use this highly effective method of control.
Recent research has shown that clearing the
droppings even on a less frequent basis, up
to once per fortnight can still be highly
effective at controlling horse worm burdens.
If the stocking density is high then more
frequent clearance of droppings may be
necessary, but, for average stocking densities
(1-2 horses per acre) once a fortnight
clearance of droppings is highly effective
and a much more achievable target for
most horse owners.
Faecal Worm Egg Counts (WEC)
Measuring the concentration of worm eggs in
the horse’s faeces can not only tell us a how
severe an infestation of worms that particular
horse has, but it can also be used to measure
how effective the anthelmintic (wormers) drugs
are being.
In any group of horses there are usually only
a few (10-20% or 1 or 2 out of every 10)
that are significantly contaminating the pasture
with a high concentration of worm eggs in
their faeces. Performing WEC’s allows us to
identify which of the group of horses have
these high concentrations of worm eggs in
their faeces, so we can target our treatments
at these horses. A lot of owners believe
that they need to try to keep their horses
‘worm-free’ and the aim of their worm
management programme is to try to achieve
this. One of the new ideas we need to
embrace is the concept of horses having an
acceptable level of worm burden. In the same
way that we recognise that trying to rid the
human body of all bacteria is not only
impossible but also really bad for our health
and well-being. We need to realise that the
presence of a few worms in our horses may
actually be good for them. There is research
to suggest that acceptable levels of worms in
horses may help prevent nasty conditions such
as Grass Sickness and research from human
medicine points to low levels of worm burdens
being protective against allergic respiratory
conditions such as asthma. As more and more
work is done in this area, there is likely to be
more valuable information like this.
Worm egg count (WEC) results in the region
of 200-400 eggs per gram of faeces should
be considered as acceptable and only horses
returning results higher than this will require
treatment with a wormer.
Another use of the WEC tests is to measure the
effectiveness of the wormers we use to treat the
horses. If a faecal sample is tested 2 - 4 weeks
after a treatment with a wormer and the result
is not zero, then there is a strong suspicion
that there is a resistance problem in the worm
population, on that premises, to the wormer
used. This is valuable information which vets
can use to help formulate and adapt the worm
control programme on that premises. Using
WEC’s as part of the standard worm control
programme for our horses is something we are
all going to have to get used to and the ability
to identify those horses that actually need
treatment and only treat those horses is not
only a more efficient use of the worming drugs,
it also makes financial sense, too. Nobody
would think it sensible to treat our horses with
antibiotics every 6 weeks just in case there
might be an infection, so we need to
appreciate the way we have been used
to using anthelmintics (wormers) is similarly
inappropriate.
The XLVets Equine Forum has produced a
booklet entitled ‘Effective Worm Control in
Horses’ which is available from your local
XLVets practice. The booklet explains in detail,
the modern approach to worm control and
shows plans for different age groups of
horses. If you need further advice your vet will
be happy to discuss a programme with you.
J U L I AN R I S HWORTH
...One of the new ideas we need to embrace is the
concept of horses having an acceptable level of worm
burden. We need to realise that the presence of a few
worms in our horses may actually be a good thing.