ASSESSMENT OF PHENOLICS-RELATED ANTINUTRITIVE LEVELS USING THE IN-VITRO GAS-PRODUCTION TECHNIQUE - A COMPARISON BETWEEN DIFFERENT TYPES OF POLYVINYLPOLYPYRROLIDONE OR POLYETHYLENE-GLYCOL

The use of different types of phenolic binding agents (PEA) in conjunc tion with the in vitro gas production technique for the assessment of phenolic related antinutritive factors in browse were compared. During a grazing trial by goats, three fractions, grazed leaves (GL), ungraz ed leaves (UL) or stems of ungrazed leaves (US) of Robinia pseudoacaci a, together with three harvests of leaves of Cistus incanus and a summ er harvest of Fraxinus ornus or Carpinus duinensis were analysed for t otal extractable phenols (TEPH), total extractable tannins (TETa), con densed tannins (vanillin-HCl) (TECTa) and extractable and total proant hocyanidins (TEPAs and TOPAs). Gas production from the samples with or without adding insoluble polyvinylpolypyrrolidone (IPVP), soluble PVP or polyethylene glycol of different molecular weights was measured. T he kinetics of gas production were determined using the equation p = a + b (1 - e(-ct)). The effects of addition of the PBAs were assessed a s percentage changes in the rate and volume of gas production or conce ntration of volatile fatty acids (VFA). Levels (mg g(-1) DM) of TEPH v aried from 4.9 to 100.4, TETa from 0.6 to 58.0, TECTa from 1.0 to 64.6 , and TEPas or TOPAs from 5.7 to 283.0 and from 12.4 to 331.4. Except for PVP360 which depressed fermentation, addition of 200-500 mg of the other PBAs to rumen liquor/buffer or a tannin free hay, did not affec t (P > 0.05) fermentation. The highest increase in gas production was achieved with PEG4, PEG8 and PEG10 followed by PVP10, PVP40 and IPVP a fter 12-24 h incubation. The percentage increase in gas production as a result of adding the PEGs was best associated (r = 0.83-0.96; P < 0. 01) with the higher concentrations of total VFAs after 96 h incubation and was also best related (r = 0.89-0.91; P < 0.01) to the levels of extractable condensed tannins (TECTa and TEPAs) in the browse. It was concluded that PEGs were more effective than PVPs in eliminating pheno lic related antinutritive factors and would be preferred for use in co njunction with the gas technique for the assessment of phenolic relate d antinutritive factors in feeds.