Interactions between trace minerals and growth promoting practices in beef cattle.

Trace minerals (TM) are necessary to support optimum animal growth. While TM requirements to prevent deficiency were recently updated, the requirements of beef cattle to support optimal performance remain ill defined. Advancements in animal genetics and utilization of technologies to promote growth of feedlot cattle have dramatically advanced production efficiencies in the beef industry. Trace minerals (Co, Cu, Fe, I, Mn, Se and Zn) are integral in a variety of growth processes in the body, including supporting metalloproteins involved in DNA synthesis, collagen production, energy utilization and critical antioxidant enzymes. Over 80% of feedlot cattle are estimated to receive hormone implants to enhance growth and efficiency. Recently, we examined the effect of feeding no supplemental TM, TM supplemented at NRC recommendations, or TM supplemented at industry recommended concentrations (all inorganic sources), fed to Angus cross steers receiving no implant or implanted with Component TE-IS, followed by Component TE-200 on d 56. Harvested on d 124, HCW was, as expected, improved (P = 0.0001) by implant, but HCW was also improved by 15 kg (P = 0.01) in steers supplemented at industry TM concentrations vs. those receiving no supplemental TM. Additional work is needed to clarify the potentially greater need for TM in cattle receiving hormone implants. Introduction of beta adrenergic agonists revolutionized late stage finishing cattle performance, increasing feed efficiency, ADG, and often HCW of cattle. In a series of studies we have found that increasing supplementation of Zn (from a combination of inorganic and organic sources) to steers fed ractopamine hydrochloride increases cattle performance (ADG, feed efficiency, and HCW in some studies) during the ractopamine feeding period. Zinc is thought to inhibit breakdown of the intracellular signalling molecule, cAMP, perhaps potentiating the growth response. Alternately, demand for Zn and other TM may simply be greater due to increased growth rates. We recently found the retention of Zn and N to be positively correlated and that both ractopamine hydrochloride and Zn increase N retention in steers. It seems likely that growth enhancing technologies influence TM requirements of cattle, and further work is needed to determine TM requirements that optimize cattle performance and maximize producer profitability.