WORM EGG COUNTS
Parasite resistance is a common problem on many equestrian properties and as such, we recommend our clients conduct worm egg counts on their properties and implement a strategic parasite control program. The fact is, some commercially available wormers are not effective if the population of parasites on a particular property is resistant. On the flip side, the overuse of an effective wormer will eventually result in resistance.
We offer in-house worm egg counts and the cost associated with this test is $35. So that we can keep the cost of this test as low as possible, we ask that clients provide credit card details at the time of sample delivery.
Sample collection kits are available for pick up from our office at 4/4-6 Guelph Street, Somerville. Kits can be collected between 9am and 4pm on Tuesdays.
Please download our submission form.
Please find following, our general recommendations for using the results of faecal egg counts in a strategic worming program;
These general recommendations are for horses over 2 years of age.
- Administer wormer when faecal egg count > 200 epg.
- Calculate and administer adequate dose of wormer based on accurate body weight.
- Conduct faecal egg count reduction test at least once per year or when choosing a wormer that contains an active ingredient to which resistance has been reported such as benzimidazoles (e.g. fenbendazole or oxibendazole).
The aim of the faecal egg count reduction test is to estimate the efficacy of a wormer by comparing eggs per gram of faeces of an individual horse at the time of treatment and again 10-14 days after treatment. Average reduction in egg counts should be 90% or greater. If the reduction in egg count is less than 90% it is likely that drug resistant worms are present.
- Be aware that the time required for eggs to reappear after treatment with a wormer depends on the following;
- Active ingredient in wormer.
- Parasite burden of the horse.
- Eggs generally reappear 8 to 10 weeks after treatment with ivermectin.
- Eggs generally reappear no less than 12 weeks after treatment with moxidectin.
- Eggs generally reappear 4 to 6 weeks after treatment with a benzamidazole compound.
We believe this is how the general rule of worming every 6 weeks found its way into equine folklore. Once upon a time, before the invention of ivermectins the main equine wormers were benzamidazole based. It was logical at the time to worm based on the reappearance of eggs in the faeces and this was an effective strategy for a number of years until resistance began to emerge to this class of drug due to it’s overuse.
Additional Management Strategies for Reducing Parasite Burdens
- Manure removal from pasture, especially areas of high horse density or pastures holding more vulnerable horses (e.g. yearlings).
- Manure removal from stables and appropriate disposal.
- Do not spread fresh manure on pastures.
- Avoid placing manure piles where rain could wash infective larvae onto pastures.
- Pasture rest to reduce larvae numbers.
- Tilling and reseeding pastures to reduce numbers.
- Alternate grazing of pastures between horses and ruminants. Grazing by one species will destroy strongylid parasites of the other. Note that Trichostrongylus axei is cross-infective and can potentially cause clinical disease in horses.
- Harrowing pasture to expose larvae to dessication. This is effective only in dry weather. In wet weather this will result in disperal of larvae and will probably increase worm burden in the horses grazing that pasture.
- Avoid overcrowding of paddocks.