NEMATODES
Small redworm (small
strongles/cyathostomes) are the most common parasite to effect your
horse. They are up to 2.5cm long,
thin and can range in colour from white to red. Small redworm larvae are picked up
by horses whilst grazing. Historically, the key period of risk was
spring and summer. However, recent climatic changes have led to hot,
dry summers, and warm, wet autumns and winters. Spring and autumn have
now become the periods of greatest risk. Furthermore, recent studies
that have involved monitoring pasture infectivity; have shown high
levels of infective larvae present on turnout paddocks, even in
January after snow. This means that “winter worming” is now just as
important as worming during the summer grazing season. Small redworm
larvae can develop into adults within a period of five weeks. In the
autumn, however, their development is prolonged and they remain in
cysts as tiny inhibited larvae (early L3 larvae) or as larger late 3rd
and 4th stage larvae within the gut wall. These are broadly termed
“encysted larvae” but in the late winter or spring, an unknown trigger
causes these larvae to resume their development. The symptoms of
simultaneous emergence of large numbers of 4th-stage larvae are colic,
weight loss, diarrhoea and can cause devastating damage to the large
intestine, sometimes resulting in death. Even before they emerge,
large numbers of encysted larvae can cause fatal disease. The encysted
larvae stages can account for over 90% of the total small redworm
burden so controlling these larval stages is an important part of any
equine worm control programme. Horses particularly at risk are
those that have grazed on heavily stocked and contaminated pasture,
have not been regularly wormed regularly or have mixed with other
horses that have not been treated regularly and the risk increases for
horses under 6 years old.
Horses that are subject to effective
worming procedures and where good pasture management is practised
through out the year will pass fewer small redworm eggs in their
droppings so the levels of worm burden will be less and therefore the
risk of encysted larvae will be reduced. However these worms have a
life cycle of between 6 weeks and up to 2 years so caution must be
exercised even when pastures have been rested.
It is possible for horses with an early EL3
infestation to appear healthy and well. Furthermore, if a Faecal Egg
Count (FEC) test is carried out on an EL3-infected horse, the small
redworm burden may not appear to be high because it is mainly present
in the dormant EL3 form.
Only 2 anthelmintics have claims of
efficacy against encysted small redworms they are:
Fenbendazole (5 day course)
Moxidectin (single dose)
Symptoms:
Diarrhoea, rapid and severe weight loss, colic and can even KILL
your horses. As cyathostomes
attach themselves to the gut and are absorbed into it they reduce
the efficacy of the gut wall to absorb essential nutrients which can
lead to general ill thrift in the horse and an incapability to
utilise properly a balanced diet.
