Evidence for the inhibition of the terminal step of ruminal alpha-linolenic acid biohydrogenation by condensed tannins.

J Dairy Sci

Eidgenössische Technische Hochschule Zurich, Institute of Animal Science, Universitaetstrasse 2, CH-8092 Zurich, Switzerland.

Published: January 2009

AI Article Synopsis

  • The study examined the effects of condensed tannins (CT) and saponin extracts on the ruminal biohydrogenation of alpha-linolenic acid (ALA) in a controlled environment using a basal diet of grass-clover hay.
  • Supplementation with CT reduced fiber and protein degradation in the rumen and suppressed methane production, while the saponin extract had minimal effects on fermentation but increased protozoal counts.
  • CT treatments resulted in a 20% reduction in ALA biohydrogenation, likely due to decreased organic matter degradability; also, the CT-extract diet altered the profiles of biohydrogenation intermediates compared to the control diet.

Article Abstract

Effects of condensed tannins (CT), either via extract or plant-bound, and saponin extract on ruminal biohydrogenation of alpha-linolenic acid (ALA) were investigated in vitro. Grass-clover hay served as basal diet (control). The control hay was supplemented with extracts contributing either CT from Acacia mearnsii [7.9% of dietary dry matter (DM)] or saponins from Yucca schidigera (1.1% of DM). The fourth treatment consisted of dried sainfoin (Onobrychis viciifolia), a CT-containing forage legume, in an amount also providing 7.9% CT in dietary DM. All diets were supplemented with linseed oil at a level contributing 60% of total dietary ALA in all treatments. Diets were incubated for 10 d (n = 4) in the rumen simulation technique system, using the last 5 d for statistical evaluation. Fatty acids were analyzed in feed, feed residues, incubation fluid, and its effluent. Data were subjected to ANOVA considering diet and experimental run as main effects. Both CT treatments reduced ruminal fiber and crude protein degradation, and lowered incubation fluid ammonia concentration. Only the CT extract suppressed methane formation and shifted microbial populations toward bacteria at cost of protozoa. The saponin extract remained without clear effects on fermentation characteristics except for increased protozoal counts. The extent of ALA biohydrogenation was 20% less with the CT plant, but this probably resulted from reduced organic matter degradability rather than from an inhibition of biohydrogenation. After incubation analysis of incubation fluid effluent and feed residues showed a considerable proportion of the 3 biohydrogenation intermediates, cis-9, trans-11, cis-15 C18:3, trans-11, cis-15 C18:2, and trans-11 C18:1, which did not occur in the initial feeds. Only the CT-extract diet led to a different profile in the effluent compared with the control diet with trans-11 C18:1 being considerably increased at cost of C18:0. This could have been achieved by suppressing protozoa and enhancing the bacterial population, thus removing potential microbes involved in biohydrogenation and increasing competition between bacteria involved in biohydrogenation and others. The elevation of trans-11 C18:1 as the precursor of cis-9, trans-11 conjugated linoleic acid formed in body tissue and mammary gland is probably favorable from a human health point of view.

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Source
http://dx.doi.org/10.3168/jds.2008-1117DOI Listing

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