Effect of Harvest Stage and Ensiling on Contents of Crude Nutrients, Amino Acids, Riboflavin and Secondary Plant Metabolites of Winter Catch‐Crops <scp> <i>Vicia sativa</i> </scp> , <scp> <i>Vicia villosa</i> </scp> and <scp> <i>Vicia pannonica</i> <

ABSTRACT This study compares properties of fresh and ensiled vetch forage harvested at different growth stages: bud‐, flowering‐, pod formation‐ and pod filling stage. The research focused on three vetch species— Vicia sativa L. (VS), Vicia pannonica Crantz. (VP) and Vicia villosa Roth. (VV)—each represented by two varieties and cultivated in Northern Germany. The forages were ensiled with buffered formic acid and Lactobacillus plantarum on a laboratory scale in 1 L jars for 90 days, with four replicates per variety at each harvest stage. First, the effect of maturity stage on silage properties of whole‐crop vetch was studied. The crude protein (CP), amino acid (AA), ether extract, crude ash and riboflavin contents declined during maturation ( p &lt; 0.05), while the unfavourable secondary metabolites γ‐glutamyl‐ß‐cyanoalanine (GCA), ß‐cyanoalanine (BCA) and vicine were mainly present at the pod filling stage of VS. These findings suggest that earlier growth stages are preferable as forage. Secondly, the study compared silages to the respective fresh forage to evaluate the degradation of undesired secondary plant metabolites and the conserving effect on CP, AA and riboflavin during ensiling. The ensiling process conserved CP, AA and riboflavin, while GCA, BCA and vicine were broken down ( p &lt; 0.05) with reduction rates of 88.2%–99.8%, 64.8%–100% and 99.9%–100%, respectively. These results indicate that ensiling is an effective conservation method for vetch forage. The occurrence of undesirable microorganisms was suppressed, as evidenced by the absence or minimal presence of butyric acid, ethanol and ammonia‐N.