Assessment of phenolics-related antinutritive effects in Mediterranean browse: a comparison between the use of the in vitro gas production technique with or without insoluble polyvinylpolypyrrolidone or nylon bag

Abstract

Eight Mediterranean browsing species were analysed for neutral and acid detergent fibre, lignin, crude protein, total extractable phenols (TEPH), tannins (TETa), condensed tannins (vanillin-HCl) (TECTa) and extractable or total proanthocyanidins. Dry matter (DM) disappearance (in situ) or gas production (in vitro) with or without adding insoluble polyvinylpolypyrrolidone (PVP) at the ratio of 1:1 PVP/substrate were measured over 96 h incubation. Concentrations of volatile fatty acids (VFA) in the supernatant of gas production were determined at the end of incubation. The browse varied largely in their concentrations of fibre components. Phenolics concentration (mg g −1 DM) of TEPH varied from 34.9 to 124.3; for TETa from 6.8 to 114.2 and for TECTa from 2.0 to 27.7. The Quercus spp. had the lowest potential and rate of DM degradation or gas production. The gas technique was more efficient than nylon bag for the assessment of antinutritive effects in browse. The response of the browse to PVP treatment as increase (%) in gas production varied between species and changed over time. After 96 h incubation, the change in total VFAs concentration was strongly related ( R 2 = 0.84; P < 0.01) with the increase (%) in gas production. However, none of the phenolic assays was related ( P > 0.05) to the increase (%) in gas production at all incubation periods. The reasons for the absence of a relationship were discussed and attributed to the nature of the phenolic assays used and to the fact that several types of phenolic compounds contribute to the biological response. It was concluded that while further research to optimize treatment conditions and link particular phenolic compounds with the increase in gas production was needed, the gas production technique appears to have a good potential use for the assessment of phenolicrelated antinutritive effects in feeds.