Abstract
Three studies were completed to evaluate the effects of Cu, Zn, and Mn source on preferential intake, trace mineral status and rainfall-induced metal loss of salt-based mineral supplements. Mineral supplements were formulated to contain 2,500, 5,500, and 4,000 mg/kg of Cu, Zn, and Mn, respectively. Supplements differed only by source of Cu, Zn, and Mn, which were hydroxychloride, organic, or sulfate sources. In Exp. 1, the 3 formulations were offered simultaneously for 18 wk to pre-weaned beef calves (4 pastures; 17 calves/pasture) within separate containers inside covered cow-exclusion areas. Consumption averaged 21 ± 2.4 g/calf daily (sum of all 3 sources), with a greater (P < 0.001) percentage of the total intake coming from the hydroxychloride- vs. organic- or sulfate-sources of Cu, Zn, and Mn. In Exp. 2, the same sulfate and hydroxychloride formulations were randomly assigned to pastures (n = 4 pastures/treatment) containing 18 to 20 cow-calf pairs/pasture. Treatments were offered for 20 wk within covered areas designed to assess cow and calf intake separately. At weaning, liver biopsies were collected from 4 cow-calf pairs/pasture (n = 16 cows and calves/treatment). Source of Cu, Zn, and Mn had no effect on voluntary mineral intake among calves (P = 0.44) and cows (P = 0.14). Calves consuming mineral containing hydroxychloride-sources of Cu, Zn, and Mn tended (P = 0.06) to have greater ADG over the 20-wk period compared to calves consuming sulfate-sources of the same elements (1.09 vs. 1.06 kg/d; SEM = 0.013). Mineral status of cows and calves was not affected (P ≥ 0.17) by source of Cu, Zn, and Mn. In Exp. 3, each of the mineral formulations from Exp. 1, were exposed to a 10.2 cm precipitation event delivered in three equal 3.4 cm applications within a week. To accomplish this, 750 g of mineral was placed into Buchner funnels (177 cm 2) on 20 to 25 µm pore filter paper. Deionized water (pH adjusted to 5.6) was poured over the mineral. Total leaching losses of Cu, Zn, and Mn were less (P < 0.001) for formulations containing hydroxychloride- vs. organic- and sulfate-sources. These results imply that, when offered a choice, calves preferentially consume mineral supplements formulated with hydroxychloride vs. sulfate or organic sources of Cu, Zn, and Mn. In addition, hydroxychloride sources of Cu, Zn, and Mn are less susceptible to rainfall-induced leaching losses compared to sulfate and organic sources.
156 Injectable trace mineral supplementation on grazing beef cows: effect on overall mineral status and fertility