86 - Anthelmintic Resistance in Angus Bulls Participating in Regional Performance Tests

Resistance to anthelmintics, more commonly referred to as “de-wormers,” has been on the rise in parasites that affect cattle. Parasite infection can have severe impacts on calf productivity resulting in reduced profitability. Therefore, we sought to better understand anthelmintic resistance in Appalachia by surveying Angus bulls entering performance tests in VA and WV. During a four-year period, over 1050 Angus bulls were tested at bull development facilities in Wardensville, WV, Culpeper, VA, and Wytheville, VA. Fecal samples were collected at arrival and 14 days later for determination of fecal egg count (FEC) reduction. Upon arrival, all bulls received either fenbendazole (Wardensville, WV) or moxidectin (both VA tests). In Wardensville, treatment with albendazole had a 96.7% FEC reduction, whereas, treatment with moxidectin at Culpeper and Wytheville stations resulted in FEC reduction of 29% and 34.9%, respectively. Gain during these 14 days was significantly lower for bulls from Wytheville (0.87 kg/d) than those of Culpeper and Wardensville (1.87 and 2.1 kg/d; respectively). These data can be partially explained by higher bull FEC after treatment in Wytheville (101 eggs/g) compared to bulls in Wardensville and Culpeper (3.4 and 46.4 eggs/g respectively). Additionally, there was a negative correlation between delivery FEC and average daily gain. Taken together these data demonstrate resistance to moxidectin in bulls from the Appalachian region, and that elevated parasite infection may have contributed to reduced gain during the transition period.