Influence of Supplemental Copper, Manganese, and Zinc Source on Reproduction, Mineral Status and Performance in a Grazing Beef Cow-Calf Herd over a Two-Year Period

The objective of this experiment was to evaluate the effects of supplemental Cu, Mn, and Zn source on reproduction, trace mineral (TM) status, and performance in a grazing cow-calf herd in eastern Colorado over a 2-yr period. Crossbred (Angus and Angus x Hereford; n=261) three year old beef cows were stratified by expected calving date, BW, BCS, and liver TM status and randomly assigned to 1of 6 pastures. Pastures were then assigned to 1of 2 free-choice mineral treatments (n = 40-45 cows per pasture; experimental unit = pasture), resulting in 3 replicate pastures per treatment for each year of the 2 year experiment. Treatments consisted of: 1) hydroxychloride TM (HTM; 100% of the Cu, Mn, and Zn from IntelliBond C, M, and Z, respectively), and 2) inorganic + organic TM (IOTM; 75% of Cu, Mn, and Zn from sulfate TM and 25% of Cu, Mn, and Zn from amino acid complexes of Cu, Mn, and Zn). Replicates were rotated among pastures approximately every 28 d in order to minimize pasture effects. Free-choice mineral feeders were used to provide current NRC-recommended concentrations of Cu, Mn, and Zn continuously for 2 years. Blood samples and liver biopsies were obtained from every cow before the initiation of the experiment and then from a subgroup of animals (20 random animals/ replicate) at the end of Year 1 and the same 20 animals/replicate at the end of year 2. At the end of year 1, liver Cu and Zn concentrations were greater (P < 0.05) in HTM compared to IOTM supplemented cows. At the end of year 2, liver Cu concentrations were greater (P < 0.05) and Zn concentrations tended (P < 0.06) to be greater in HTM compared to IOTM supplemented cows. However, over the two year experiment, mineral intake, BW, BCS, pregnancy rate to artificial insemination, overall pregnancy rate, 205-d adjusted weaning weight, kg of calf weaned per cow exposed, and plasma Cu, Mn, and Zn concentrations were similar across treatments. These data indicate that under conditions of this experiment, source of TM had no impact on beef cattle production parameters but TM source did impact liver Cu and Zn concentrations over the 2 year experiment.