Some useful tips on worm
control are as follows:
How can resistance
develop? Resistance develops due to artificial selection
by wormers. Selection caused by the level of exposure
to a wormer and the level of effectiveness that
wormer has against a parasite.
·
Exposure to wormer: … High frequency of
dosing - "too -frequent" treatments with the same
molecule of wormer predisposes the parasite to
develop resistance. … Under dosing - parasites
are exposed to the drug, but not a sufficient
dosage to kill them and so they start to build
immunity to its effect.
·
Effectiveness of wormer: … Wormers that
are less than 90% effective against parasite select
for resistance as those left behind produce resistant
descendants.
To
rotate or not rotate
The idea to rotate horse wormers to reduce the
risk of resistance is actually derived from sheep
farming. However no studies in sheep, let alone
horses, have shown that rotation makes a significant
difference in the length of time it takes for
resistance to occur
As
such some experts are now of the opinion that,
instead of rotation, a better way to reduce the
risk of resistance building up is to:
· Worm less frequently, i.e. use wormers with
long dosing intervals
· Not use wormers with known resistance for routine
worm control, and
· Not under-dose, but to give your horse the correct
dose according to its weight.
| Active ingredient
of horse wormer |
Dosing interval |
Known resistance
in the UK |
| moxidectin
(EQUEST) |
13 weeks |
NO |
| praziquantel
(EQUITAPE) |
6 months* |
NO |
| ivermectin |
8-10 weeks |
NO |
| ivermectin+praziquantel |
8-10 weeks |
NO |
| pyrantel |
4-8
weeks |
Yes, reported
resistance in small and large redworms1 |
| fenbendazole |
6-8
weeks |
Yes, widespread
small redworm resistance |
| *Treatment
for tapeworm recommended in the spring and
autumn. 1. Coles G C et al 1999, Veterinary
Record, 145: 408 |
Suggested
worming programme Together EQUEST and EQUITAPE
offer a comprehensive, effective and simple worm
control programme.
A programme that does not require a 5 day course
for the control of encysted small redworm, nor
a double dose for the control of tapeworm. Plus
a programme which fulfils the requirement to reduce
the risk of resistance building up, with long
dosing intervals for EQUEST (every 13 weeks) and
EQUITAPE (6 months) and no known resistance to
either wormer.
As
such a programme from which there is no need to
rotate off, but one you can stick to using year-on-year**.
Now doesn't that make worming your horse simple!
| |
Spring |
Summer |
Autumn |
Winter |
| Routine roundworm
(including all stages of encysted small
redworm) and bot control |
EQUEST (single dose
every 13 weeks) |
EQUEST (single dose
every 13 weeks) |
EQUEST (single dose
every 13 weeks) |
EQUEST (single dose
every 13 weeks) |
| Tapeworm control |
EQUITAPE (single dose) |
|
EQUITAPE (single dose) |
|
**
Variability in worm challenge and susceptibility
does occur and your veterinary surgeon should
be contacted for specific advice. As with any
preventative medicine programme periodic assessment
is advisable.
|
