Growth and economic performance of grazing steers as influenced by growth implant and anthelmintic strategy
DOI:
https://doi.org/10.21423/bovine-vol1998no32.2p19-24Keywords:
animal parasitic nematodes, anthelmintics, benzimidazoles, contamination, controlled release, economics, fenbendazole, grazing, growth, head, helminths, ivermectin, liveweight gain, parasites, pastures, shedding, steers, weight gainAbstract
460 yearling steer calves were grazed on 6 improved mountain pastures in western North Carolina for 128 days. The pastures were matched into 3 pairs based on acreage, topography and botanical composition. Within each pair of pastures, calves in 1 pasture received a sustained release bolus containing ivermectin (Ivomec SR Bolus), and calves in the other pasture were drenched with fenbendazole at 5 mg/kg (Safe-Guard Suspension 10%). In the fenbendazole treatment groups, a loose mineral and fenbendazole mix (Safe-Guard Free-Choice Mineral) was provided to the calves for 5 days beginning at day 28 and day 56 to provide 5 mg/kg/animal over the 5 day period. Within each pasture, calves received 1 of 4 commercial implant treatments: Ralgro (36 mg zeranol), Synovex-S (20 mg estradiol benzoate and 200 mg progesterone), Revalor-G (8 mg estradiol-17 beta and 40 mg trenbolone acetate) or no implant. Calves receiving the Ivomec SR Bolus had a significantly higher average daily gain than the Safe-Guard treated calves (0.96 vs. 0.88 kg/day) resulting in a 11.93 kg advantage. At the end of the trial, 8 of 29 randomly sampled calves on the Safe-Guard treatment were shedding parasite eggs. No calf receiving the ivermectin bolus was shedding clinically significant levels of parasite eggs. When value of gain, cost of product, labour and equipment costs were considered, it was determined that the cattle treated with the Ivomec SR Bolus returned $6.70/head more than the cattle treated with Safeguard. Implanted calves gained more than the non-implanted calves with average daily gains of 0.83, 0.95, 0.95 and 0.94 kg/day for the control, Ralgro, Synovex-S and Revalor-G cattle, respectively. An economic analysis, which included the value of gain, the product cost and the labour to administer the implants, showed an average of $15.31 greater return for the implanted calves compared with control calves. It is suggested that the Ivomec SR Bolus should be considered for calves grazing large mountain pastures for extended periods.
