Ensiling sugar beets: Sampling, chemical composition, and digestibility of mixed sugar beet silage

Abstract

The aim of this study was to 1) identify the sampling method for representative sampling of mixed beet silages, 2) describe the chemical composition and digestibility of mixed silages, 3) assess the extent of crude protein (CP) degradation in rapeseed meal when co-ensiled with beets, and 4) compare large-scale with laboratory-scale ensiled silages. Ensiling was performed in November 2021 and January 2022 to produce two silage sets. A total of 7 mixed silages were made as large-scale ensiling in round bales by co-ensiling high dry matter (DM) sugar beets with either maize silage, grass/clover silage, grass seed straw, dried beet pulp, fresh beet pulp, or rapeseed meal. At the same time, beets ensiled with maize silage, grass/clover silage, grass seed straw, and fresh beet pulp were replicated as laboratory-scale ensiling in vacuum bags. After 30, 92, and 181 days of ensiling, two samples were obtained from mixed silages ensiled in bales: 1 bore sample using a silage sampling drill and 1 large sample from the side of the bale. The large sample was minced in an industrial bowl cutter to get a representative homogeneous sample. To investigate the degradation of CP in rapeseed meal co-ensiled with beets, Dacron bags containing pure rapeseed meal were added to bales during baling. The DM of mixed silages ensiled in bales and sampled as a large sample varied between (mean ± SEM) 248 ± 8.10 and 363 ± 8.10 g/kg at 181 days of ensiling, and pH for all mixed silages was below 4.2 at 30 days of ensiling. Mixed silage content of ethanol at 181 days of ensiling varied between 17.1 ± 12.7 and 140 ± 12.7 g/kg DM for mixed silages ensiled in bales and sampled as a large sample. Differences between sampling methods were found for mixed silage DM, pH, NH₃, acetate, L-lactate, ethanol, ethyl acetate, propyl acetate, maltose, and mannitol. For most mixed silages, these differences disappeared after 92 days of ensiling, where the silages were stable and could be representatively sampled using a silage drill. The organic matter digestibility (OMD; in-vivo calculated from in-vitro) of the mixed silages after 181 days of ensiling varied between 685 ± 3.27 and 903 ± 6.50 g/kg OM for mixed silages ensiled in bales and sampled as a large sample. Chemical composition varied depending on mixer feed. No evidence of CP degradation in rapeseed meal was found when co-ensiled with beets. Furthermore, using laboratory-scale ensiling in vacuum bags as a model for large-scale ensiling may result in an overestimation of fermentation products and an underestimation of fermentable sugars.