Resistance can’t be diagnosed by fecal egg counts alone and results can easily be misinterpreted DULUTH, Ga. — May 12, 2008 — With recent hype about anthelmintic-resistant parasites, producers are getting offers for free anthelmintic evaluations and diagnoses from all directions. “Some animal health companies are offering fecal egg count reduction tests (FECRT) as the gold standard for diagnosing anthelmintic-resistant parasites,” says Dr. Frank Hurtig, Director of Merial Veterinary Services. “FECRTs alone are not accurate indicators of anthelmintic resistance, especially when not conducted by third-party experts.”¹ FECRTs can easily be misinterpreted if collected or analyzed improperly, Dr. Hurtig says. Merial recommends that producers have their veterinarian collect fecal samples for them and then work with independent state labs or vet schools for FECRT analysis and additional tests. Dr. Hurtig says producers should not rely on commercial labs or a manufacturer’s lab. The following are some guidelines that are followed to help achieve the most accurate results:
Sample 14 to 20 days following treatment
Sample at least 10% of the herd or 30 animals
Collect a 5 gram sample — being sure to accurately measure the sample weight
Avoid misidentification of false parasite eggs
If strongylid-type eggs are noted, have a coproculture performed to differentiate species present
“While an FECRT can help producers identify specific parasite problems in their herd, truly assessing anthelmintic efficacy requires well-controlled critical studies where animals are sacrificed and parasites are counted,” Dr. Hurtig says. “One of the most important things producers should look at in FECRT results is what parasite eggs are present and know what that means for their herd.” FECRT results may indicate large numbers of parasite eggs; however, Dr. Hurtig says it is highly common for the eggs to be from Cooperia. “Cooperia are the dose-limiting nematodes for endectocides, meaning that producers must use the approved dose rate to have the desired effect,” Dr. Hurtig says. “But, Cooperia have little economic impact and are considered minimally pathogenic cattle nematodes, unlike main targets like Ostertagia.” Cooperia also are prolific egg producers, so a small number of Cooperia can result in a higher egg-per-gram count than would be expected with the same number of another parasite. “The bottom line is that there are only two well-documented cases of parasite resistance to ivermectin in cattle in the United States,2,3 and one of the cases was with stocker cattle being managed very intensively for a period of 23 years,” Dr. Hurtig says. “It’s best for producers to rule out more common causes for lack of efficacy before looking to resistance.” For producers wanting to protect their herd and their endectocide investment, Dr. Hurtig recommends using endectocides that are backed by the manufacturer, such as Merial, the maker of IVOMEC® Brand Products. All IVOMEC Brand Products are backed by a 100% product satisfaction guarantee. “Merial encourages producers to be informed about resistance and to not let data be misused, such as by indicating that Cooperia eggs in an FECRT indicate resistance,” Dr. Hurtig advises. “If producers are genuinely seeing a lack of efficacy and poor herd performance, they should see their veterinarian and work through third-party outlets to determine the problem.” Merial is a world-leading, innovation-driven animal health company, providing a comprehensive range of products to enhance the health, well-being and performance of a wide range of animals. Merial employs more than 5,000 people and operates in more than 150 countries worldwide. Its 2007 sales were nearly $2.5 billion. Merial Limited is a joint venture between Merck & Co., Inc. and sanofi-aventis. For more information, please see www.merial.com . ### IVOMEC Plus (ivermectin/clorsulon): Do not treat cattle within 49 days of slaughter. Do not use in dairy cattle of breeding age or in veal calves. IVOMEC (ivermectin) Pour-On: Do not treat cattle within 48 days of slaughter. Do not use in dairy cattle of breeding age or in veal calves. IVOMEC 1% Injection for Cattle and Swine: Do not treat cattle within 35 days of slaughter. Do not use in dairy cattle of breeding age or in veal calves. Do not treat swine within 18 days of slaughter. IVOMEC EPRINEX® (eprinomectin) Pour-On for Beef and Dairy: No meat or milk withdrawal is required when used according to label. All IVOMEC Brand Products: Do not use in other animal species not on the label as severe adverse reactions, including fatalities in dogs, may result. Consult your veterinarian for the proper treatment timing in your area in order to avoid potentially serious side effects associated with grubs. 1Stromberg BE. Fecal Egg Count Reduction Test (FECRT) Standardization Recommendations for Cattle — An Introduction. Proceedings AAVP 2007:73.
2Smith LL, Gasbarre LC. The Identification of Cattle Nematode Parasites Resistant to Multiple Classes of Anthelmintics in a Commercial Cattle Population, in Proceedings. Joint Meeting of AAVP and ASP, 2004:54.
3Smith LL, Gasbarre LC. Evaluation of Individual or a Combination of Anthelmintics in a Commercial Cattle Population Where Anthelmintic Resistant Parasites Had Been Observed the Previous Year, in Proceedings AAVP 2005:63-64. ®IVOMEC and EPRINEX are registered trademarks of Merial.
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