Page 81 - The Veterinary Care of the Horse

Strategic treatments target species of worms and stages of development that cannot be

detected by FEC testing, e.g. small redworm larvae that often encyst in the gut wall during
VetBooks.ir autumn and winter. Until recently a late autumn/winter treatment with moxidectin was
recommended for the majority of horses to eliminate the encysted larvae. However, with the

new blood test for small redworm it will be possible to identify and treat only those horses
that need it. A blood test is recommended for animals with low or moderate risk; a strategic

treatment with moxidectin is recommended for high risk animals and those with an FEC of
more than 200 EPG.

Targeted treatment

Treatment is based on the results of diagnostic tests which include the blood test for small
redworm, FECs and a blood or saliva test for tapeworm.

The advantages of targeted treatment are:
• individual animals with high egg counts causing most of the pasture contamination are

identified

• unnecessary treatments are avoided
• the risk of worm resistance to the anthelmintics is reduced

• there is less contamination of the environment from drug residues in the droppings

• there is often a reduction in cost

FREQUENCY OF WORM EGG COUNTS

Worm egg counts are recommended at regular intervals throughout the grazing season
between March and October. If the egg count is below 200 EPG no treatment is required. The
frequency of testing is influenced by the anthelmintic used, as each has a different interval

before worm eggs reappear after use. With moxidectin the minimum recommended interval
for testing after treatment is 12 weeks, for ivermectin and fenbendazole it is 8 weeks, for

pyrantel embonate 6 weeks.

Most adult horses have low small strongyle infection levels; younger and older horses
tend to have higher infection levels. Regular FEC testing is an essential part of caring for

your horse.

TESTING FOR RESISTANCE

If resistance is suspected, a faecal egg count reduction test is helpful. This involves testing

dung samples from a number of horses in the field before dosing and again 14 days later. The
selected horses should have a FEC of at least 200 EPG. If significant numbers of eggs are