Reply from Dr. John Byrd:
When Horsemen’s Laboratory reports that a horse has a negative sample (no eggs found on counting chamber) it could possibly have 25 eggs/gm, as stated in the fine print at the bottom of the receipt. That is because the test we use is the McMaster Technique that has been used to evaluate the effectiveness of deworming medications for years.
When speaking of deworming schedules we most often base it on Strongyles because they are by far the most popular parasite we find. 30-33% of samples Horsemen’s Laboratory receives are positive. Over 95% of those positive samples are positive for Strongyles.
As far as deworming is concerned Horsemen’s Laboratory’s general recommendations are to deworm horses that are classified as negative 1-2 times a year and give something that contains praziquantel at least once a year for tapeworms as there is not a good test for tape worms. We occasionally find them, but if we do not find them it does not mean the horse definitely does not have them. There are presently 3 products that are readily available that contain praziquantel; Equimax, Zimecterin Gold, and Quest Plus.
There may be circumstances that dictate we may want to alter our general rule for deworming, for example:
1. Age of horse?
2. What part of the country the horse is located in?
3. How the horse is kept?
4. How often and how well is the environment kept clean of manure?
5. What is the previous history of horse?
6. When was last deworming?
7. What was last deworming medication used?
8. Whether a horse seems to fall in to the low, medium, or high egg shedding category?
If you are cleaning your pastures and stall on a daily basis what part of the country you live in will not have much of and impact on your parasite problem. Because even in the warmer climates that are ideal for egg hatching and larval development it will still take at least 2 days after passing for the eggs to develop into infective stage larva and leave the pile of manure.
Also, if you are checking your horses every 3 months until we establish what category they are in we should be able to catch any problem shedders before they contaminate your pastures to any extent.
One thing I want to stress, there are only a very few, if any statements that can be made about parasitology that are absolute and precise. This does not mean that we should ignore results and things we have learned about evaluating parasite control programs. Horsemen’s Laboratory is looking at ways we may better help horse owners learn more about this very important aspect of horse health. If anyone has suggestions of topics they would like more information about concerning parasites in their horses please let us know.