Combined Ensiling of Tropical Beans and Sugarcane Stalks: Effects on Their Secondary Metabolites

In this study, the effect of mixed silage on the chemical composition, ensilability, in vitro cellulase digestibility and some of their plant secondary metabolites (PSM) were assessed. The lab-scale silage mixes were made in triplicate from sugarcane (Saccharum spp.) stalk and Canavalia ensiformis or Mucuna pruriens beans (Santa Clara, Cuba). Sugarcane stalks and beans were mixed at a ratio of 40:60 (on DM basis), respectively, in combination with a mixture of microbial inoculants (Lactobacillus acidophilus, and two Kluyveromyces fragilis strains, 4 x 10(5) colony forming units (CFU)/g of fresh matter). Before and after ensiling, the chemical composition, ensilability and contents of some PSM (trypsin inhibitor, L-canavanine, total tannins, L-dopa and phytic acid) were determined. A complete factorial design to assess the effect of the ensiling time (30, 60 or 90 days), the legume type (LT) and their interactions on the assessed parameters were performed. A better silage fermentation quality of the M. pruriens-sugarcane mixed material [e.g., lower (p < 0.05) pH and ammonia N content and higher (p < 0.05) concentration of lactic acid] was observed as compared with the C. ensiformis-sugarcane mixed material. The ensiling process reduced (p < 0.001) the studied PSM, being higher (p < 0.001) in the M. pruriens-sugarcane silages than in the C. ensiformis-sugarcane silages [trypsin inhibitor (86 vs. 76%); L-canavanine (70 vs. 53%); total tannins (54 vs. 50%); L-Dopa (89 vs. 86%)], except for phytic acid (65 vs. 68%), respectively]. It was concluded that ensiling enhances the quality of the feeds by predigestive reduction of the amount of secondary plant metabolites.