1 A survey of anthelmintic resistance in Angus bulls participating in centralized performance tests in Appalachia

Abstract

Abstract Parasitism in weaned calves and anthelmintic resistance can negatively impact performance and reduce profitability. To better understand anthelmintic resistance, bulls were evaluated for fecal egg count (FEC) at performance test facilities in Virginia and West Virginia. Over a two-year period, 532 Angus bull calves were tested at bull development facilities in Wardensville, WV (n = 274), Culpeper, VA (n = 167), and Wytheville, VA (n = 91). Fecal samples were collected upon arrival and 14 d later, representing the warm-up or transition period. At arrival, bulls were treated with either albendazole (Wardensville) or moxidectin (both VA tests). Data were analyzed via the general linear model of SAS with fixed effects of station and year. Correlation analysis of arrival FEC and transition ADG was analyzed using the correlation procedure in SAS. The average FEC reduction (FECR) in bulls at Wardensville was 98%; whereas, FECR at Culpeper and Wytheville was 46% and 16% respectively. Average FEC of bulls at Wytheville, Culpeper and Wardensville were different (P < 0.05) after treatment and had a FEC of 133, 51, 3 eggs/g, respectively. Transition ADG favored bulls from Wardensville and Culpeper (2.43 and 2.31 kg/d; P > 0.05) where bulls at Wytheville had lower ADG compared to either station (1.03 kg/d; P < 0.01). Correlation between arrival FEC and transition ADG was negative for bulls in Wardensville (-0.22; P = 0.0003). This same response was not observed at other stations. Lack of a correlation was most likely due to infection level being so low that abundant feed resources masked effects of parasitism, or parasitism was so great that all cattle transitioned poorly. Nonetheless, these data clearly demonstrate the efficacy of albendazole in significantly reducing fecal egg output in bull calves and identify potential resistance to moxidectin.