Effect of zinc and copper source on finishing steer feedlot performance and incidence of footrot

Abstract Text: A commercial feedlot study compared a combination of inorganic and organic copper and zinc trace minerals (CON) to basic copper chloride and zinc hydroxychloride trace minerals (BCHZ) on performance and carcass characteristics as well as the incidence of footrot in feedlot cattle.  Crossbred yearling steers (n=1471, initial BW 273 ± 10 kg) were allocated to pens by sorting every 5 steers into 1 of 2 pens prior to processing within cattle origin.  Pens were blocked by cattle origin and were assigned randomly to 1 of 2 treatments (8 pens/ treatment).   Treatments consisted of adding 19 (finishing) or 25 (growing) mg/kg of copper and 108 (finishing) or 136 (growing) mg/kg of zinc. However, CON consisted of copper sulfate, and a 65% zinc sulfate and 35% zinc methionine complex, whereas BCHZ consisted of basic copper chloride and zinc hydroxychloride trace minerals.  Total dietary zinc ranged from 94-146 mg/kg based on analysis.  Total dietary copper ranged from 15-29 mg/kg.  Upon initiation of the trial, all steers were implanted with Revalor IS.  Cattle were fed a growing ration for the first 75 d of the trial and then transitioned to the finishing ration.  Cattle were re-implanted with Revalor IS after the growing period and implanted again with Revalor 200 on d 154.  Mean d on feed was 216.  All steers were fed Zilmax at 8.3 mg/kg of DM for 20 d at the end of the feeding period followed by a 3-d withdrawal period before harvest.  Live performance was calculated from pen BW shrunk 4%. Data were analyzed using the Glimmix procedure of SAS.   There was a 4 kg significant difference in initial BW, thus initial BW was used as a covariate in the model.  There were no differences in DMI, ADG, final BW, and G:F (P ≥ 0.14).  Hot carcass weight, dressing percentage and marbling score were also unaffected (P ≥ 0.17) by source of trace mineral supplementation.  There was no difference (P ≥ 0.28) in total morbidity or footrot treatments in terms of total number of pulls or re-treated animals when comparing CON to BCHZ.  Cattle that received basic copper chloride and zinc hydroxychloride trace mineral supplement performed similar to cattle that received a conventional trace mineral program. 

Keywords: cattle, feedlot performance, trace mineral