82. A Fecal Egg Count Reduction Test Comparing the Efficacy of Generic Injectable Moxidectin to the Pioneer Brand in Weaned Beef Calves

Abstract Cattle are exposed to gastrointestinal parasites creating a negative impact on overall production and health. Internal parasites are typically managed with oral, topical, or injectable commercial products and many are available in pioneer and generic formulations. However, the widespread use of these products has created drug resistant parasite populations, and the Cooperia species, which is highly prevalent in cattle, is known to be resistant to macrocyclic lactones. The objective of this study was to compare the efficacy of pioneer moxidectin (Cydectin) with generic moxidectin (Tauramox) and a negative control. Efficacy was accessed using a fecal egg count reduction (FECR) test and growth performance in grazing beef calves. This study was conducted at the University of Arkansas Beef Cattle Research Unit located in Fayetteville, Arkansas. Steer and heifer calves (n = 27, BW = 234 kg) from a herd with known macrocyclic lactone resistance were assigned to 1 of 3 treatment groups based on their stratified d -8 fecal egg count (FEC). On d 0, calves were either a) injected with Cydectin at 0.2 mg/kg of body weight (n = 10); b) injected with Tauramox at 0.2 mg/kg of body weight (n = 9); or c) calves received no anthelmintic product (n = 8). FEC were completed on days -8, 0, 14, and 28, and body weights were taken on days –8, 0, 14, 28, and 46. Calves were grazed together and maintained on grass pastures for the duration of the study. Log-transformed mean FEC, average daily gain (ADG), and body weights were analyzed using the MIXED procedure of SAS 9.4. Significance was declared at P < 0.05 and tendencies were observed between 0.05 ≤ P < 0.10. The results indicated that on day 14 post treatment, Tauramox had lower FEC than the other treatments (P < 0.0495). However, FECR on day 14 was 64.5% for Tauramox compared to 40% for Cydectin. On day 28 post treatment, FECR for Tauramox treated calves were still lower than the negative control (P < 0.0417), but not different than the Cydectin treatment. On day 28, FECR was 29.2% greater for Tauramox and 43.3% greater for Cydectin when compared to day 0. There were no significant differences in body weights between treatments (P > 0.3755); however, overall ADG (P < 0.0130) was 0.15 kg for Tauramox, 0.28 kg for Cydectin, and -0.10 kg for the negative control calves. Although Tauramox slightly outperformed Cydectin, neither product suppressed FEC to the >90% FECR standard at any time.