25 Copper, manganese, and zinc source and concentration in free-choice mineral supplements influence production throughout three cow-calf production cycles

The effects of Cu, Zn, and Mn source and concentration in free-choice mineral supplements on mineral status, reproduction, and performance of grazing beef cows and their offspring were evaluated over 3 production cycles. Treatments targeted: 1) 1X NASEM requirement for Cu, Zn, Mn from sulfate sources (1X SUL), 2) 1X NASEM requirement for Cu, Zn, Mn with hydroxychloride sources (1X HYD), and 3) 0.5X NASEM requirement for Cu, Zn, Mn with hydroxychloride sources (0.5X HYD). Crossbred (Angus and Angus x Hereford; n = 160) beef cows were stratified by expected calving date, body weight (BW), body condition score (BCS), and liver mineral status and randomly assigned to one of eight replicates. Replicates were then assigned to one of the three treatments (n = 20 cows per replicate), resulting in three replicates for 1X SUL and 0.5X HYD and two replicates for 1X HYD in each year of the 3-yr study. Replicates were rotated among pastures approximately every 28 d to minimize pasture effects. Free-choice mineral feeders were used to provide Cu, Zn, and Mn treatments which were formulated into complete mineral supplements with a target intake of 114 g·cow-1·d-1. Elemental S was included in the free-choice mineral supplement at an inclusion rate of 12% S to serve as a potential antagonist to Cu. Additionally, pasture forage concentrations of Mo were > 2 mg Mo/kg DM. Body weights and BCS of the cows were obtained at study initiation and at the end of yr 1, 2, and 3. Liver biopsies were obtained from all of the cows before study initiation, and then a subset of cows (10 cows per replicate) at the end of yr 1, 2, and 3. Over the 3-yr study, mineral supplement intake was approximately 1.5 times the targeted intake for all treatments. Cow BW and BCS were similar (P ≥ 0.91) across treatments over the 3-yr study. Liver Cu, Zn, and Mn concentrations and pregnancy rate to AI were greater (P < 0.05) in cows receiving 1X HYD and 0.5X HYD compared with 1X SUL after yr 2 and 3 of the study. Actual weaning weights were greater (P < 0.05) in 1X HYD and 0.5X HYD supplemented animals compared with 1X SUL after yr 3 of mineral supplementation. Hydroxy Cu, Zn, and Mn supplementation improved Cu, Zn, Mn liver status, pregnancy rate to AI, and actual weaning weights of calves compared with sulfate sources of Cu, Zn, and Mn.