Recently one of our clients at Horsemen’s Laboratory asked about the accuracy of our testing methods. Horsemen’s Laboratory was established in 1991 and since then we have tested over 66,000 samples. In addition, 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 and is owned by Craig R. Reinemeyer, DVM, PhD, Dipl. ACVM to confirm our results. Both of these laboratories placed horses in the same category of egg shedding as Horsemen’s Laboratory, confirming our results.

There are several factors that can affect the testing accuracy, the most common issue occurs when the sample is collected. We instruct clients to completely fill the container we provide and pack the sample firmly. Often we receive samples consisting 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.

  1. 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 easier to find and count in the sample.
  2. To insure Horsemen’s Laboratory has enough of a sample to properly test.

The fresher the fecal sample is also improves results. Therefore, we recommend collecting samples on Monday and mailing them immediately. We receive 80-85% of samples within 3-5 days. 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, when samples are packed firmly, the eggs have only developed slightly if at all. Occasionally it takes longer for samples to reach Horsemen’s Laboratory and if they are firmly packed the larvae in the eggs again will appear only slightly developed. Samples less tightly packed will have dead larvae floating in solution on the counting chamber, since each egg only produces one larva we just count the larvae.

There are many factors that affect the accuracy of fecal eggs counts, plus the fact that 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 far better than guessing the effectiveness of your horses’ worm control program.