Comparison of a reimplant program using Synovex Choice and Synovex Plus versus Revalor-XS in feedlot steers

Five experiments were conducted with beef steers to compare the effects of a reimplant program (Synovex Choice-Synovex Plus, SC-SP) on feedlot steer performance and carcass characteristics with those of a 1-implant program of Revalor-XS (RXS). Studies were conducted in Ordway, Colorado (n = 820); Morgan, Minnesota (n = 751); Cactus, Texas (n = 1,972); Larned, Kansas (n = 1,509); and Wellington, Colorado (n = 1,500). Steers were administered either Synovex Choice on d 0 followed by Synovex Plus between 52 and 92 d or Revalor-XS on d 0. Each experiment was conducted as a randomized complete block design with pen as the experimental unit. Cattle were blocked by arrival date and were randomly allotted, several at a time, to a pen within a block. On d 0, implants were administered and steers were weighed. Steers were fed typical finishing diets and were slaughtered in commercial facilities for carcass evaluation. Statistical analysis models for individual studies included the fixed effects of treatment and random effects of block and block-by-treatment interaction; additional effects were included as appropriate. Within each experiment, there were treatment differences in carcass-adjusted final BW, total BW gain, ADG, DMI, G:F, HCW, QG, and YG. However, there were no consistent differences between the 2 treatments for the various variables across the 5 experiments. From a numerical perspective in 4 of 5 experiments, carcass-adjusted final BW, total BW gain, ADG, and HCW were increased for SC-SP compared with RXS. Gain efficiency was numerically improved in all 5 experiments for the reimplant program of SC-SP versus a single dose of RXS. Percentage of US Prime plus Choice carcasses numerically favored the RXS treatment compared with SC-SP in 4 of 5 experiments. In the majority of experiments (3 or more), USDA YG 1 and 2 were numerically increased, and USDA YG 4 decreased for SC-SP versus RXS.