Effect of invasive slug populations (Arion vulgaris) on grass silage: I. Fermentation quality, in-silo losses and aerobic stability

This study aimed to explore how invasive slug populations of Arion vulgaris influence fermentation quality, in-silo losses and aerobic stability of grass silage, and the efficiency of silage additives and wilting to improve the quality of silages from slug contaminated crops. The effect of four levels, including control, of a slug contaminated grass crop, was evaluated in laboratory scale. The crop used was wilted to two dry matter (DM) levels: low (253 g DM/kg) and high (372 g DM/kg). Adult slugs were applied to the low DM crop corresponding to 5 (low level), 10 (medium) and 20 (high level) 7-g sized A. vulgaris per m2 in an assumed harvested regrowth yield of 2.5 ton DM per ha. For the high DM crop, the applied slug levels corresponded to 6 (low level), 12 (medium) and 24 (high level) slugs per m2. DM level, the effect of four additive treatments, control (C), inoculation with Lactobacillus plantarum (LP), a formic, propionic and benzoic acid mixture (ACID) and a chemical additive containing benzoic acid, NaNO2, hexamethylenetetramine and propionic acid (CHEM) were tested. Increasing slug contamination gave increasing quality reductions both in silages containing 253 and 372 g DM/kg. Compared with untreated silage, LP-treatment did not improve silage fermentation quality of contaminated crops. Treatment with ACID and CHEM, however, considerably improved the quality of heavily contaminated silages. The much higher crude protein concentration in slugs compared to grass crop made slugs a more “difficult-to-ensile” material. Wilting of the harvested crop to 372 g DM/kg was not sufficient to control silage fermentation of slug contaminated crop. With contamination levels from 138 to 553 g fresh slug weight/kg crop DM, efficient silage additives were able to ensure acceptable fermentation quality of grass silages.