LAUSR

Trace minerals (TM) are required for many biochemical processes and support optimal animal growth. However, as animal genetics and feed technologies in the beef industry have advanced, our understanding of the TM requirements of modern cattle has lagged. Recently, Zn and Cu have emerged as potential targets for better understanding the interaction between nutrition and growth-promoting technologies like anabolic implants and β-agonists (BA). Both Zn and Cu are phosphodiesterase inhibitors, potentially maintaining cAMP concentrations, potentiating the BA signal. Zinc supplementation well above national recommendations can improve ADG or HCW in finishing cattle during the BA feeding period, and N retention is increased by both Zn and BA supplementation, suggesting a major role for Zn is in protein accretion. Interestingly, Cu status of feedlot steers appears to affect ADG during the BA period, where steers with moderate liver Cu and 10 mg Cu/kg diet DM gaining more than steers with high or low Cu status. Anabolic implants likely improve growth through altering protein deposition, degradation and satellite cell proliferation, processes that can be linked to Cu and Zn metalloproteins. Implanting cattle decreases both plasma and liver Zn, and heifers receiving a long-lasting implant had greater HCW when supplemented with 100 mg Zn/kg DM when compared with 30 mg Zn/kg DM. It is apparent Cu status and supplementation also affect the response to hormone implants. Steers supplemented with 20 mg Cu/kg DM had greater liver Cu concentrations and a lesser response to an implant than steers supplemented with 10 mg Cu/kg DM. Current state of knowledge suggests TM status and diet concentrations can impact the response to growth promoting technologies. Much remains to be learned about cattle requirements for dietary TM, and the appropriate TM concentrations to optimize feedlot cattle performance.