Effects of Single Administration of Half-dose Injectable Doramectin, Full-dose Injectable Doramectin, or Fenthion on Fecal Egg Counts, Growth Performance and Carcass Characteristics in Cattle

carcass quality

Abstract

This clinical trial was designed to compare the effects of a single administration of half-dose doramectina, full-dose doramectin, or fenthionb only on growth performance, hot carcass weight, carcass quality grade and fecal egg count in a group of cattle of western US origin and finished in eastern Nebraska. Two hundred ninetyfive crossbred steers (mean weight 667 lb; 303 kg) were purchased from auction barns in California, processed and allocated to the study in Idaho, and finished in a commercial feedlot in eastern Nebraska. At arrival to the backgrounding yard in Idaho, the calves were randomly assigned to one of three treatment groups: 1) fenthion only (0.5 oz/cwt); 2) half-dose (0.55 ml/cwt) of injectable doramectin; or 3) full-dose (1.1 ml/cwt) of injectable doramectin. Cattle in the fenthion treated group were poured with fenthion for ectoparasite control. At arrival, individual weights were recorded and fecal samples collected and assayed to determine nematode egg counts. Individual cattle weights and fecal samples were collected and recorded again when cattle were reimplanted (day 76). Carcass data were collected at harvest and individual live weights were calculated from individual carcass weight and group dressing percentage. In this study, there was significant improvement (p = 0.022) in hot carcass weight (HCW) in cattle administered full-dose doramectin as compared to cattle administered half-dose doramectin or fenthion pour-on only. Average daily gain (ADG) was greater in the group treated with full-dose doramectin than in the fenthion only group (p = 0.016). Significant differences in fecal egg counts were not found between experimental treatment groups (p = 0.078).