Absorption and Retention of Trace Minerals in Adult Horses

Absorption and retention of Cu, Mn, and Zn were compared when feeding diets supplemented with oxide, sulfate, or organic-chelated forms of the minerals. Six mature Miniature Horses were used in the replicated 3 × 3 Latin square-designed experiment. The experiment was conducted in three 17-d periods, consisting of 10 d of diet adaptation followed by a 7-d total fecal and urine collection. Horses were fed a diet of 40% coastal Bermudagrass and 60% concentrate formulated to meet the energy, protein, Ca, and P requirements for maintenance of mature horses. Copper, Mn, and Zn were supplemented to provide 140 to 180% of the NRC (1989) recommended dietary concentrations for these minerals and were supplied in oxide, sulfate, and organic-chelate forms. Following total collections of feces and urine, feed, fecal, and urine samples were processed and analyzed for Cu, Mn, and Zn concentrations by atomic absorption spectrophotometry. Absorption of Cu, Mn, and Zn in all forms was low compared with previous studies, but systemic retention of these minerals was high. The cause of this disparity is unknown, although experimental error is unlikely. There were no differences in the absorption or retention of Cu, Mn, and Zn among the three forms of mineral supplements. Mature, idle horses may not be appropriate animals in which to evaluate absorption of various forms of trace minerals.