Assessment of Phenolics-Related Antinutritive Levels using theInVitro Gas Production Technique: A Comparison Between Different Types of Polyvinylpolypyrrolidone or Polyethylene Glycol

Abstract

The use of different types of phenolic binding agents (PBA) in conjunction 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), ungrazed leaves (UL) or stems of ungrazed leaves (US) of Robinia pseudoacacia, together with three harvests of leaves of Cistus incanus and a summer harvest of Fraxinus ornus or Carpinus duinensis were analysed for total extractable phenols (TEPH), total extractable tannins (TETa), condensed tannins (vanillin-HCl) (TECTa) and extractable and total proanthocyanidins (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. The kinetics of gas production were determined using the equation p = a + b (1 - e -ct ). The effects of addition of the PBAs were assessed as percentage changes in the rate and volume of gas production or concentration of volatile fatty acids (VFA). Levels (mg g -1 DM) of TEPH varied 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 affect (P > 0.05) fermentation. The highest increase in gas production was achieved with PEG4, PEG8 and PEG10 followed by PVP10, PVP40 and IPVP after 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 phenolic related antinutritive factors and would be preferred for use in conjunction with the gas technique for the assessment of phenolic related antinutritive factors in feeds.