P.O. BOX 231, BALCLUTHA 9240
BALCLUTHA CLINIC
Wilson Road - Phone (03) 418-1280
Fax (03) 418-1750
Merchandise Direct (03) 418-1281
[email protected]
MILTON CLINIC
Union Street - Phone (03) 417-8032
Fax (03) 417-8031
Horses have many species of internal and intestinal parasites, some of which are harmless, but many of
which are harmful and some deadly. Controlling parasites is important for your horse’s wellbeing, and
management of the process must be taken seriously. Ultimately, the concept of parasite control is to reduce
the load of parasites an animal has to deal with by reducing the number of infectious worms on the pasture.
An integrated approach is required, with worming with drench products (anthelmintics) an important aspect
of parasite control, but coming second to pasture management.
Picking up faeces from the paddock regularly (at least twice a week) is the most important thing you
can do to control the parasite burden your horses are exposed to – this reduces the number of
infectious larvae on the pasture by 80-90%. The number of larvae can be reduced further by cross
grazing 2-3 weeks after the horses have come out. You can cross graze with almost any other species of
animal (other than equids like donkeys or zebras), such as sheep, goats, cattle, or even deer (or geese, if
you have enough!). Feeding hard feed and hay above the ground also reduces the ingestion of infectious
larvae, e.g. use an un-tip-overable feed bucket (good luck with that – try putting the bucket in an old tyre)
and feed hay in a hay rack rather than on the ground. If foals are a part of the system, ensure that foaling
paddocks are kept clean, i.e. they were not used for foaling last season, and have not been grazed by
weanlings or yearlings within the last 6-12 months. Under New Zealand conditions, harrowing is a BAD idea.
It never gets hot and dry enough to kill the larvae, and simply acts to spread eggs and larvae around the
paddock to contaminate a larger area. In a drought in Northland there may be some benefit, but virtually
never south of Auckland.
The best way to gauge a horse’s worm status is by evaluating the faeces for the presence of worm eggs
(faecal egg count, or FEC). This will approximate the burden of worms for all species except for a stage in
the cyathostome (“redworm”) lifecycle, which is encysted (dormant) inside the gut wall. At Clutha Vets, the
cost for this is $12 for one sample, or $6.75 for multiple samples (get a group together!).
The most practical test for drench effectiveness is what’s colloquially called a “drench check”. First a FEC
sample is taken and assessed. If enough eggs are present (you can’t reduce eggs further than zero!), the
horse is drenched with the product concerned, and another FEC done 10 days later. If the drench is
effective, there should be no eggs present in the second sample.
In terms of which wormer we recommend, it’s a question of active ingredients rather than brand. As a rule of
thumb, combination drenches with multiple actives are more likely to be effective than single active
ingredient ones, and will continue to be effective over the longer term. The old advice of rotating drench
families annually is outdated – using combination drenches is much more effective at preventing drench
resistance. If a drench check has shown resistance to a wormer in the past, don’t use that again.
Different families have different effectiveness against the various parasites. Fenbendazole (Panacur) is
effective against nematode worms, including dormant redworms; Macrocyclic lactones (MLs), such as
moxidectin, ivermectin, abamectin, are effective against nematodes and bots; praziquantel is effective
against tape worms. Only moxidectin and fenbendazole are effective against dormant redworms, and it is
important to include these in your worming schedule. This is the purpose of a “Panacur Bomb”, which is 5
days of Panacur (fenbendazole) in a row; to get rid of the dormant redworms safely, without having them all
hatch at once as happens if you dose with e.g. ivermectin, which can be fatal if large numbers of dormant
redworms are present. BUT, resistance to Panacur is common. Moxidectin is probably most effective against
dormant redworms, and only requires a one-off dose. BUT… Resistance of other worms to moxidectin is
common, so it’s a good idea to use a combination product!!! See below.
Tape worms don’t actually cause any harm to the gut, but may be implicated in some forms of colic. It’s for
this reason that I advocate occasional treatment of tape worms – why take the risk. In addition, most
products have a tape killing drug in them anyway!
Dose schedule
Should you drench adult horses every 6 weeks? If they need it based on FEC, and your drench is 100% on a
drench check, then yes. But with a caveat – why is their intake of larvae so high that they are developing a
worm burden that quickly? If your drench is effective based on a drench check, and their FEC is rising that
quickly, there must be a problem with the grazing system. Every drench you give increases the likelihood
that resistance will develop, so giving them as sparingly as possible is the goal!
Foals
-
ML (moxidectin, ivermectin, abamectin) at 8 weeks
8 week intervals until winter with ML + Praziquantel
Weanlings/yearlings
- One dose of ML + Praziquantel in spring
- If poo is picked up, then 3 doses 10 weeks apart over summer
- If poo is left, keep dosing every 6-8 weeks (but bear in mind that this increases the risk for
developing resistance)
Mares
-
1-2 weeks pre-foaling, give a drench. Two days later, wash the udder and perineum to remove
any adherent eggs.
Clean foal boxes with steam or 10% NaOH
Otherwise, as for other adults
All adult horses
- If poo is picked up, 3 times per year, can be less if a large amount of cross-grazing with other
species occurs.
- Early spring with ML + Praziquantel
- End of summer with an ML
- End of autumn with ML + Praziquantel
- Or, drench based on FEC testing
Incoming horses
- Moxidectin + Praziquantel on arrival
- Quarrantine 24-48 hours, pick up and dispose of poo
- FEC on arrival and 10 days after drenching
Retail products and active ingredients
UltraMox – moxidectin, praziquantel, oxfendazole
Equitak EXCEL (also comes multidose)– abamectin, praziquantel, oxfendazole
PARADE – ivermectin, praziquantel
Equest plus tape – moxidectin, praziquantel
Triumph – ivermectin, oxbendazole, praziquantel
Panacur - fenbendazole
Compiled by Dr Isobel Topham, BVSc
YOUR VETERINARIAN
“THE ANIMAL HEALTH PROFESSIONAL”