PS12-13. Comparative Parasitism and Production Performance in Beef Calves Over A 90-Day Grazing Period When Treated with Two Parasiticides.

Abstract Control of gastrointestinal nematodes is a critical aspect of extensive beef production. Uncontrolled, parasites can erode welfare and performance in affected production classes of cattle. The current study was conducted to compare two anthelmintics: a broad spectrum dual-acting combination endectocide (T01, doramectin + levamisole) and an extended-release single ingredient parasiticide (T02, eprinomectin). Evaluations of fecal egg count reduction and growth performance in weaned beef calves were conducted, as well as an economic comparison in costs for the two treatment groups. Calves were randomly assigned to one of two treatment groups where they received either T01 (n = 230) or T02 (n = 230) on day 0. Calves were individually weighed at time of enrollment, and at study completion on day 90. Fecal samples were collected from a subset of calves from each treatment group on day 0, day 21, and day 90 for a total of 52 calves, with 26 represented per treatment group. At enrollment, calves had similar weights (P = 0.67) between treatments T01 (280.68kg), and T02 (281.6kg). Calves had similar final body weights (P = 0.27) at completion of the study on day 90, and similar average daily gain (P = 0.29) between treatment groups. Of the pooled fecal egg count samples taken on Day 21, cattle in T01 receiving a combination of doramectin + levamisole tended to have fewer fecal egg count (P = 0.09) than cattle in T02 receiving eprinomectin, resulting in a 95% fecal egg reduction in calves receiving T01 from Day 0 sampling, and 85% reduction for calves in T02. At the current dosage and cost per mL, treatment cost for calves at the initiation of the study was significantly (P < 0.0001) lower for calves in T01 ($4.40 USD/animal) compared with calves in T02 ($7.84 USD/animal). While there was not a difference in performance as indicated by final body weight and average daily gain, the findings in this study demonstrate both the effectiveness and economic benefit of using a dual-acting combination endectocide compared to use of an extended-release single ingredient parasiticide for control of gastrointestinal nematodes.