Influence of polyethylene glycol on in vitro gas production profiles and microbial protein synthesis of some shrub species

The aim was to determine effects of addition of polyethylene glycol (PEG) on in vitro gas production and microbial protein synthesis of the shrub species Acacia constricta, Acacia shaffneri, Calliandra eriophylla, Condalia lycioides, Cordia parvifolia, Larrea tridentata and Mimosa biuncifera, which are commonly consumed by grazing small ruminants in semiarid regions of Mexico despite the abundance of tannins in their foliage. Three individual samples (a minimum of 10 plants of each) of each shrub species were collected from different areas and prepared for chemical and secondary metabolite analysis. In vitro evaluations for each sample of each shrub species were completed in three incubation runs in different weeks using calibrated glass syringes in a 7×2 factorial design (i.e., 7 shrub species×2 treatments with or without PEG). In vitro gas production after 24 and 96h, partitioning factor (PF), metabolizable energy (ME) content, efficiency of microbial protein synthesis (EMPS), and volatile fatty acids (VFA) were determined. A shrub species×PEG interaction (P