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By John Byrd, DVM
How do you know my horse has worms? How do you know you got rid of the worms my horse had? These two questions were commonly asked when I dewormed horses as a general equine veterinarian. My standard response was that the drug companies tell us they work.
When the daily dewormers came on the market many of my clients requested that I get these dewormers for their horses. I often told them I thought it was unnecessary because most of the horses were already being dewormed every 2 months. In addition, 90% of the horses I cared for in southern California were kept in clean box stalls 22 hours a day except when they were being ridden or exercised. I did not see how these horses could have many worms, if any at all. Therefore, I decided to seek the answers to these common questions for myself by doing fecal egg counts before I dewormed my horses.
What I found was that less than 1 out of 20 horses had any eggs in the stool sample to indicate they were infected with adult worms. After consulting with several experts in equine parasitology and recognizing that no one was performing routine fecal egg counts for horse owners, I started Horsemen’s Laboratory to fill this void. I felt owners should have the opportunity to know whether or not their horses had worms rather than just treating them blindly.
For several years now researchers have known that many of the worms that horses have were becoming resistant to the dewormers that were being used to treat them. There also appears to be a link between the over use of these dewormers and the developing resistance. What appears to be occurring is that the dewormers kill most of the worms that are sensitive, leaving only the resistant few to mate with each other. These worms then create more worms that are resistant and soon we have large populations of worms that are now resistant to the dewormer. Performing fecal egg counts can help owners identify if their horse has resistant worms and can also indicate which dewormers an owner should be using.
Stool samples will also indicate which horses are passing the most eggs and therefore identifying the worst contaminators of the pasture. Horses can then be dewormed according to how rapidly they are spreading eggs that will become infective larva on their pasture and in their environment. Research shows that 20% of the horses in a pasture are responsible for 80% of the eggs in a pasture.
Regular stool samples will give horse owners the peace of mind that they have a worm control program that is working to protect their horse from the effects of these parasites. There is no other way of evaluating whether or not you have an effective worm control program. By testing a stool sample before automatically deworming, you may also be helping to slow the development of resistance to dewormers by only deworming when it is necessary. In the long run this may reduce the cost of their worm control program and give owners the confidence that it is truly effective.
HORSEMEN’S LABORATORY has made it affordable and convenient to have fecal egg counts done on your horses. Visit www.horsemenslab.com or call (800) 544-0599 and take advantage of this great service to help protect your horse from worms.
By John Byrd, DVM
Recently one of Horsemen’s Laboratory clients asked about the accuracy of our testing methods. Horsemen’s Laboratory was established in 1992 and since then we have done over 46,000 samples. Over the years we have sent samples to the University Of Illinois School Of Veterinary Medicine Department Of Parasitology and to East Tennessee Clinical Research, Inc., a very competent laboratory that does extensive testing and research in the field of parasitology, owned by Craig R. Reinemeyer, DVM, PhD, Dipl. ACVM. The results found at all three laboratories were very comparable; placing each horse in the same category as far as egg shedding was concerned.
There are several factors that can affect the accuracy of the results of a sample. The most common generally occurs when the sample is collected. To help address this we have printed instructions in red stating “to fill the container completely” right on the plastic bag that the container is sent in. Many times we receive the sample and it consists of only a few small twigs of used hay and a couple of used oats.
There are 2 reasons we need the container filled completely and packed firmly.
I. Is to insure we have plenty of sample to check.
II. When packed firmly it reduces the space for oxygen in the container, which the eggs need for larvae to develop.
This preserves the eggs so they are much easier to find and count in the sample.
The fresher the sample is when it is mailed also may improve the results. Therefore, we recommend trying to collect samples on Monday and dropping them in the mail the day they are collected. We receive 80-85% of samples within 3-5 days of when they are mailed. When samples take longer and are not packed firmly the eggs have a tendency to hatch and we find the larvae swimming in the solution when viewing it on the counting chamber. However, the samples we receive that are packed firmly, the eggs have only developed slightly if at all. Occasionally it takes 10-14 days for samples to reach Horsemen’s Laboratory and if they are packed firmly the larvae in the eggs again will appear only slightly developed, while the samples packed less tightly will have dead larvae floating in solution on the counting chamber. Since each egg only produces one larva we just count the larvae.
As stated there are many factors that affect the accuracy of doing fecal eggs counts, it is not an absolute or precise science. However, it is the best evaluating system we have for determining the presence of intestinal parasites (worms) in live horses. It is also the best method of measuring pasture and environmental contamination that can lead to worm transmission from horse to horse. Therefore, it is the method of choice to evaluate individual horses and herd worm control programs. It is also the method that has been used to evaluate treatment of worms in horses and other livestock for many years. It is also far better than guessing the effectiveness of your horses’ worm control program.
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