University of Arkansas, Fayetteville Division of Agriculture
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Abstract

Utilizing small groups of naturally infected replacement heifers, fecal egg count reduction tests (FECRT) were conducted in the later months of 2007 at the University of Arkansas Savoy Research Station. Each test was 28 d in length, consisting of individual fecal nematode egg counts (EPG) and coprocultures. For the first test, the calves were ranked by beginning EPG, blocked, and randomly assigned treatment within each block. Nine to ten animals were in each treatment group. In this test, neither IVOMEC (® Merial) or IVERMECTIN (® Durvet), both delivered as an injectable at the rate of 0.2 mg of ivermectin kg-1 BW, resulted in egg count reductions of ≥ 90%. Post-treatment coprocultures relative to both products contained a mixture of Cooperia and Haemonchus spp larvae. Also in this first test, Safe-Guard (® Intervet), delivered as a suspension at the rate of 5.0 mg of fenbendazole kg-1 BW, resulted in egg count reductions of 100% (d 7 and 14) and 88-87% (d 21 and 28). Posttreatment coprocultures specific to Safe-Guard yielded only Cooperia spp larvae. In the second test, which was of follow-up treatments given immediately after the first test (animals re-sorted to treatment group), Safe-Guard at the above rate resulted in egg count reductions of 99-100% (d 7 and 14) and 54-18% (d 21 and 28). Also in the second test, Cydectin (® Fort Dodge) treatment at the rate of 0.2 mg of moxidectin kg-1 BW resulted in egg count reductions of 96-92% (d 7 to 28) and SafeGuard treatment at the rate of 10 mg of fenbendazole kg-1 BW resulted in egg count reductions of 100-88% (d 7 to 28). As was the case in the first test, post-treatment coprocultures from animals treated with Safe-Guard yielded only Cooperia spp larvae. Treatment of cattle with Cydectin resulted in coprocultures that primarily yielded Cooperia, but with a trace of Haemonchus spp larvae.

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