The changes in macromineral (Ca, P, Mg, K, Na, Cl and S) and micromineral (Cu, Fe, Mn, Zn, Co and Se) concentrations in herbage were followed during the harvesting and conservation processes of barn‐ and field‐dried hay and silage. In total, 131 herbage samples originating from 50 harvests were collected in fresh form before mowing, in wilted form at harvest and in conserved form after storage. During the harvesting process, initial Ca, Mg and Zn concentrations in herbage decreased by 7– 17% for barn‐dried hay, and initial Ca concentration decreased by 7% in herbage for silage (explained by losses of mineral‐rich and fragile plants or plant parts during the mechanical treatments). During the conservation process, mineral concentrations remained stable in barn‐dried hay, but macro‐ and micromineral concentrations increased on average by 6% and 31%, respectively, in silage (explained by loss of fermentable nutrients). Overall, in conserved hay (field‐ and barn‐dried hay), concentrations were decreased as follows: Ca 25%, Mg 15%, Cu 9% and Zn 12%; and in silage, concentrations increased as follows: Mg 12%, Na 33%, Mn 65%, Zn 13% and Se 27%, relative to the initial fresh form. During the harvesting process, ash, Fe and Co concentrations increased by factors of 0.29, 7.6 and 8.8 in wilted herbage for silage. Iron and Co concentrations in wilted and conserved herbage were linearly correlated with increasing ash concentration from a breakpoint of 100 g/kg dry matter, indicative of increasing soil contamination.