Productivity Measures in Beef Cows and Calves Following a Single Subcutaneous Injection of Long Acting Eprinomectin

The objective of this study was to elucidate the effects of a single injection of long-acting eprinomectin on economically relevant production variables in beef cows and calves. Animals from 13 cooperator herds across 7 states were stratified within herd by cow age, calf birth date, calf birth BW, and calf sex and assigned to 1 of 2 treatments; injectable doramectin (DOR; Dectomax, Zoetis, Animal Health, Parsippany, NJ; n=756) or injectable eprinomectin (EPR; Longrange, Merial, Duluth, GA; n=770;) at a rate of 1 cc/50 kg. Average duration between treatment and the end of the grazing season was 133 ± 36 d. Fecal samples were randomly collected from 20 cows from 4 cooperator herds and consisted of both spring- and fall-calving herds. Fecal samples were collected at treatment and again at the end of the grazing season to evaluate fecal egg count (FEC). Continuous and categorical data were analyzed using the MIXED and GLIMMIX procedures of SAS, respectively. Cow treatment BW and end of grazing season BW were not different (P=0.32) between treatments. However, there was a treatment × season interaction for both cow change in BW (P=0.05) and percent change in BW (P=0.08) as spring-calving EPR cows tended to have greater increases in BW over the course of the treatment period. Initial and final BCS did not differ between treatments (P=0.76). While FEC at treatment did not differ (DOR=2.60; EPR=2.75; P=0.86), cows treated with EPR had less FEC at the end of the treatment period (DOR=2.03; EPR=0.71; P=0.03) and tended to have a greater reduction of FEC over the course of the grazing season (P=0.08). Calf treatment BW, weaning BW, and ADG did not differ between treatments (P=0.49). Calves treated with DOR had a tendency (P=0.08) for a lesser incidence of pinkeye. Incidence of pinkeye was tended to be less (P=0.06) for cows treated with EPR. Fly counts were not different between treatments (P=0.14). Pregnancy rates and expected calving interval based on ultrasound were not different between treatments (P=0.25). Lack of differences observed in the current study may likely be a function of low fecal egg counts in participating herds. As part of this ongoing study, calving interval and calf feedlot and carcass performance will be assessed.