Effects of extended-release eprinomectin on productivity measures in cow-calf systems and subsequent feedlot performance and carcass characteristics of calves

The objective of this study was to estimate the impact of a single injection of extended-release eprinomectin on economically relevant production variables in beef cows and calves as well as subsequent feedlot health, performance and carcass traits of calves compared to a traditional, short-duration anthelmintic. Animals from 13 cooperator herds across 7 states were stratified within herd and assigned to 1 of 2 treatments; injectable doramectin (DOR) or injectable extended-release eprinomectin (EPR). There were no differences in pre-weaning cow or calf performance including weight, ADG, reproductive success, or weaning weight. Although EPR cows did have a lower incidence of pinkeye, there were no differences in pinkeye incidence of calves. Fecal samples collected at the start and end of the grazing season indicated a greater reduction in fecal egg counts (FEC) for EPR cows, however, FEC at each timepoint were well below threshold indicative of clinical parasitism. When evaluating feedlot performance, EPR calves tended to have lower incidence of morbidity, however there were no differences in growth performance. When evaluating carcass traits, calves treated with EPR during the pre-weaning phase had a greater marbling score and a greater average quality grade. While there were noted improvements for EPR calves during the feedlot phase including improved morbidity and quality grade, we believe that a lack of parasitic infection during the grazing season may have resulted in a lack of performance differences in this study.