Evaluation of anthelmintic resistance in Oklahoma beef cattle herds and assessment of composite sampling for herd level fecal egg count reduction testing

Abstract

Beef cow-calf producers submitted fecal samples for fecal egg count reduction (FECR) tests. Anthelmintic administration practices were not controlled, and producers were encouraged to follow standard procedures for each herd. Fecal egg counts (FEC) were determined using the Wisconsin method with alimit of detection of 1 egg per gram (EPG). Inclusion criteria included a pretreatment FEC of 25 EPG. A FECR of ≤ 90% was considered indicative of resistance. Seventeen herds submitted a total of 19 sample sets. All major classes of anthelmintics were represented except for levamisole. Injectable, pour-onand oral as well as original label and generic products were represented. Sample sets from 3 herds were excluded from the final analysis based on inadequate pretreatment FEC. Of the 16 sample sets included in the final analysis, 13 exhibited resistance based on the arithmetic mean of individual FECR tests (FECRT). In addition to individual FEC, composite samples for each herd were created using 1 gram of feces from each animal. Four grams of each composite sample were used to determine a composite FEC. Composite samples from 13 herds were included in the final analysis and 11 of 13 exhibited resistance. There was complete agreement between the individual and composite samples for the detection of resistance. Based on the results of this small survey, apparent anthelmintic resistance appears to be widespread in beef cow-calf herds in Oklahoma. Composite sampling appears to be an effectivemethod for detection of herd level resistance.