Researchers at Texas Tech University recently conducted experiments to evaluate the effects of copper (Cu) and zinc (Zn) source on performance, morbidity and humoral immune response in lightweight, newly arrived feedyard heifers. In both experiments, heifers received either an inorganic or an organic source of Cu and Zn in their receiving diets. The minerals were supplemented at rates to provide 10 ppm of Cu and 75 ppm of Zn. The first experiment looked at treatment effects on dry-matter intake, average daily gain, feed conversion and bovine respiratory disease morbidity. The second test evaluated the effects on humoral immune response to a vaccine administered on day 0 and day 14. The researchers found neither source of Cu or Zn affected DMI, ADG, feed conversion or BRD morbidity. Immune response was greater in heifers receiving organic Zn than inorganic Zn, but inorganic Cu had a greater response than organic Cu.