Page 82 - The Veterinary Care of the Horse

still present, then your vet will recommend a different treatment. A reduction of less than

90% for fenbendazole and pyrantel anthelmintics and 95% for moxidectin and ivermectin is
VetBooks.ir suggestive of resistance.

WHICH ANTHELMINTIC?

The choice of anthelmintic depends on which parasites your horse is exposed to. Diagnostic
testing and discussion with your vet can establish this. Moxidectin is generally reserved for
larvicidal treatments in the autumn/winter and praziquantel for autumn treatment of

tapeworms. Ivermectin and pyrantel are currently recommended for treatment of horses with
an FEC greater than 200 EPG during the grazing season. However, this advice may change,

so always discuss planned treatment with your vet.

General rules for worming horses

• Every horse in the field should have regular worm egg counts between March and

October, a blood test for small redworm once or twice a year depending on the risk and a
blood or saliva test for tapeworm every 6 months unless infection risk has been shown to

be low, in which case once a year in the autumn may be sufficient. All the horses should
be tested at the same time.

• It is essential that each horse receives the correct dose based on bodyweight.

• A record should be kept of the product used and the date given.
• The efficacy of the programme should be monitored by regular diagnostic testing.

• New horses with unknown history should be treated with moxidectin and tested for

tapeworm. Following treatment, they should be kept in for 3 days before going on to the
pasture.

• Pregnant mares should be treated with moxidectin a month before foaling or with
ivermectin closer to the foaling date.

• Discuss worming of foals and young horses with your vet as they are high risk.

COMMON REASONS FOR FAILURE OF ANTHELMINTIC PROGRAMMES

1 The dosing interval is too long. It is important to remember that different classes of
anthelmintic suppress the output of worm eggs for different lengths of time.

2 Failure to check all animals at the same time. A single horse that misses a treatment can
release millions of eggs onto the pasture each day and put all the others at risk.

3 A horse has not received an adequate dose. This may be because the body-weight was
underestimated or the horse rejected the feed or spat out the paste unnoticed. Under