AQHA MAGAZINE May / June 2020 AQHA May-June YB 2020 WEB LR | Page 66

PG.64
HORSE HEALTH
that the traditional approaches for parasite control
are not sustainable and new strategies are needed.
Over 60 years ago worm treatment of all horses on a
property at the same time every 6-8 weeks, rotation
of wormers and FEC were recommended. All except
the latter are now ‘out-dated, dangerous and old
school’ because the unexpected consequence was
the development of multi-drug resistance. Drugs that
were once effective are now no longer so. Whereas
once our goal was to clear a horse of all worms, due to
drug resistance (the major equine wormers belong to
just three chemical groups) the new goal is to focus on
those horses that are shedding the most worm eggs and
contaminating pastures and to use the appropriate drug
at the appropriate time – both of which require a FEC.
The FEC is a snapshot in time – numbers of eggs in
manure change with season, age and stress. Many
factors may raise or lower a horse’s shedding level, so it
is important to continue to monitor FECs at least yearly,
even on horses who are previously low shedders.
The presence and extent of resistant worms in your
horses and on your pastures can be estimated using
the faecal egg count reduction test (FERT) – a FEC
done before and 7 to 14 days after using a wormer – a
reduction of less than 90% is suggestive of resistance.
Test each anthelmintic class at least once every three
years and base you control program on drug efficacy
and horses’ shedding status. Also useful is the egg
reappearance period (the time from treatment to the
reappearance of eggs in the manure as new adult worm
populations establish), which can be used to determine
the treatment interval for your particular control plan.
piles. Grazing cattle and sheep on horse paddocks can
reduce the number of infective larvae on the grass.
However, cattle tend to eat the upper layers of
pasture and most larvae live at the bottom, so they
could lead to a higher number of infective larvae per
kg of grass. On the other hand, one sheep grazing
pasture with 3000 larvae/kg of grass could remove
90,000 infective larvae every day. Don’t spread
uncomposted manure on paddocks and because
larvae and tapeworm mites migrate across grass
manure heaps should be distant from grazing areas.
There are no blanket recommendations as each
property and horse is different and regional and
seasonal weather patterns vary so much. Routine
FEC are a direct measure of the rate at which pasture
contamination is taking place. They also confirm
the continuing efficacy of the drugs used and can
be used to determine optimum treatment intervals.
Work with your vet in conducting a FEC on your
horses and developing the best, most economical and
sustainable control program. Under-dosing increases
resistance so take care to always use the correct dose
of wormer – based on the weight of your horse using
scales or a weigh tape (available at Jenquine.com).
The recent availability of nematophagous (ie
worm-eating) fungi that will destroy larvae
in the manure is an exciting development.
Foals are at increased risk due to the peri-parturient
relaxation of resistance (PPRR) whereby a reduction in
the mares immune-suppression of worms allows her
resident population to massively increase egg output
when foals are born – maximising the worms chances
of infecting more horses. ‘Clean’ pasture are best for
foals - although adult horses observe areas for grazing
as distinct from areas for voiding urine and manure,
foals show no such aversion to grazing close to manure
DISCLAIMER: All content provided in this editorial is for general use and information only and does not
constitute advice or a veterinary opinion. It is not intended as specific medical advice or opinion and
should not be relied on in place of consultation with your veterinarian.
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