Using fecal egg count reduction tests
Many producers rely on fecal egg count reduction tests to determine which parasites are affecting their herds or whether they might have resistant parasites on their property. However, knowing the facts about the tests can help you decide whether they are the right choice for your cattle--and your wallet.
An FECRT is a field-based tool that gives a qualitative estimate of internal parasite reduction in animals treated with a parasiticide. Many producers and veterinarians use FECRTs, but because the tests have many limitations, they often are misused or misinterpreted.
"FERCTs can be a useful tool if the producer has the right expectations of what they are looking for and are aware of the test limitations," says Gary Sides, Ph.D., cattle nutritionist, Cattle and Equine Technical Services, Pfizer Animal Health. "This test can help determine which adult parasite groups are present and qualitatively evaluate the efficacy of recent deworming treatments."
Even though many producers rely on them, FECRTs may often provide misleading results, Sides notes.
"You cannot distinguish between worm species that have similar-looking eggs," Sides says. "And FECRTs are not able to account for larval stages since larvae do not lay eggs. Also, because of the immune system response, fecal egg counts do not correlate to abomasal or intestinal worm burdens in animals older than 6 months."
In calves less than 6 months of age, there can be a fair correlation between egg numbers and adult worm numbers, except for the internal roundworm genus, Nematodirus. Additionally, fecal counts will produce a false negative results for inhibited larvae of Ostertagia ostertagi (the brown stomach worm)--one of the most damaging parasites.
For FECRTs to provide valid results and show the success of an operation's deworming practices, the fecal sample must also be collected and analyzed properly.
"For the most accurate results, fecal samples must be taken all from the same animal, before treatment and again about three weeks after treatment," Sides says. "These samples also need to be taken from the rectum--not off the ground--to ensure the feces are not contaminated with soil nematode eggs. Once samples are collected and submitted, a laboratory technician will conduct an analysis and report the findings on an eggs-per-gram basis."
Sides adds that although fecal egg counts and FECRTs can be useful in evaluating your parasite-control program, conducting yearly performance evaluations and keeping accurate performance records are much more reliable and useful than counting eggs.
"To ensure that you are maximizing your parasite-control program, animals should be dosed properly, products should be stored according to label indications, and you should work with your veterinarian to design a strategic deworming program that includes all classes of dewormers in the spring and fall," Sides says. "This conversation with your veterinarian should give you a reliable, efficient way to protect your cattle and bottom line."