Changes with maturity in fibre composition and levels of extractable polyphenols in Greek browse: effects on in vitro gas production and in sacco dry matter degradation
1993
Khazaal, K. | Markantonatos, X. | Nastis, A. | Orskov, E.R.
Neutral and acid detergent fibre (NDF, ADF), lignin, crude protein (CP), total extractable phenols (TEPH), tannins (TETa), condensed tannins (vanillin assay TECTa; proanthocyanidins TEPAs) in the leaves of spring Phyllirea media (SPRG) or early summer (ESUM) and early autumn (EAUT) Carpinus duinensis, Quercus coccifera and Fraxinus ornus were studied. Gas production (in vitro) and dry matter (DM) degradation (in sacco) were also studied after incubation for up to 96 h. Concentrations of TEPH, TETa, TECTa, TEPAs and the fibre components were variable (P < 0.05) among species and except for CP were not consistently changed with degree of maturity. CP content varied from 70.5 to 132.9 (g kg(-1) DM) but was always decreased by 15-25% at maturity, whereas levels of TECTa and TEPAs were increased (P < 0.05) in C duinensis and Q coccifera but not in F ornus (P > 0.05). Concentrations of phenolics were related negatively but more significantly to gas production than to DM degradation (in sacco). Therefore, the gas test was considered to be more efficient than the nylon bag technique for the identification of feeds with antinutritive factors. Based on their phenolic content and gas production or DM degradation, the nutritive value of P media = F ornus (ESUM and EAUT) > C duinensis = Q coccifera (ESUM) > C duinensis = Q coccifera (EAUT). It was concluded that the decline in CP with maturity could make nitrogen the factor limiting intake and digestibility. This would be accentuated with an increase in the concentration of phenolics, particularly tannins.
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