Influence of supplemental copper, manganese, and zinc source on reproduction, mineral status, and performance in a grazing beef cow-calf herd over a 2-year period

Objective: This experiment evaluated the effects of Cu, Mn, and Zn source on mineral status, reproduction, and performance of grazing beef cattle in eastern Colorado. Materials and Methods: Crossbred (Angus and Angus x Hereford; n = 261) 3-yr-old beef cows were stratified by expected calving date, BW, BCS, and liver Cu status and randomly assigned to 1 of 6 replicates. Replicates were then assigned to 1 of 2 treatments (n = 40-45 cows per replicate), resulting in 3 replicates per treatment for the 2-yr experiment. Treatments consisted of (1) inorganic-organic trace mineral combination (IOC; 75% of Cu, Mn, and Zn from sulfate forms and the remaining 25% from organic AA complexes) and (2) hydroxy trace minerals (HTM; 100% from hydroxychloride forms). Replicates were rotated among pastures approximately every 28 d to minimize pasture effects. Free-choice mineral feeders were used to provide NASEM (2000) recommended concentrations of Cu, Mn, and Zn continuously for 2 yr. 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 per replicate) at the end of yr 1 (d 335 of the experiment) and 2 (d 638 of the experiment). Results and Discussion: Over the 2-yr experiment, mineral intake, cow BW, BCS, pregnancy rate to AI, and overall pregnancy rate did not differ across treatments. Calf weaning weights were also not affected by trace mineral source. At the end of yr 1 and yr 2, liver Cu concentrations were greater (P <= 0.05) in HTM- compared with IOC-supplemented cows. Liver Zn concentrations were greater (P < 0.05) in cows receiving HTM at the end of yr 1 and tended (P < 0.06) to be greater at the end of yr 2. Liver Mn concentrations were not affected (P > 0.05) by trace mineral source. Implications and Applications: Overall productivity of grazing beef cows and their calves over a 2-yr period were similar in cattle supplemented with hydroxy or a combination of sulfate and organic trace minerals. Liver Cu and Zn concentrations were greater in cows fed HTM.