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Effect of two types of tannin, in the presence or absence of PEG, on in vitro rumen fermentation in goats

AutorHervás, Gonzalo ; Álvarez del Pino, María C. ; Giráldez, Francisco Javier ; Mantecón, Ángel R. ; Frutos, Pilar
Fecha de publicación2001
EditorInstitut national de la recherche agronomique de Tunisie
Citación9th Seminar of the FAO-CIHEAM Sub-Network on Sheep & Goat Nutrition, Nutrition and feeding strategies of sheep and goats under harsh climates, p. 57 (2001)
ResumenMany non conventional feeds (forbs, shrubs and trees) fed to small ruminants under harsh climates contain diverse types and amounts of tannins that may modify their nutritive value. Polyethylene glycol (PEG) has been widely used as a tannin-binding agent to study the effect of tannins on rumen fermentation. However, its tannins deactivating action might not be universal but dependent on the type of tannin and on the parameters studied. This work was carried out to investigate the effect of two types of tannin, in the presence or absence of PEG, on several in vitro rumen fermentation parameters.
The experiment took the form of a 2 x 2 + 1 (control) design with factors consisting of two tannins [quebracho (QUE; condensed tannin) vs. tannic acid (TA; hydrolysable tannin)] and two levels of PEG (presence vs. absence; MW 6000). A non-tannin-containing feed (alfalfa hay) was chosen as the base substrate. Treatments were as follows: C = alfalfa hay (control); C + QUE; C + TA; C + QUE + PEG and C + TA + PEG. In vitro gas production, rate of degradation and DM and OM disappearance after 96 h incubation, and true digestibility and NH3-N and VFA concentrations after 24 h incubation were examined, using rumen fluid from four mature Alpine goats (rumen fistulated, fed on alfalfa). Up to 6 hours in vitro incubation, gas production was significantly lower in C + TA and no differences were observed among the other four treatments. From 8 to 30 h incubation, the reduction in gas production was statistically significant in samples treated with both quebracho and tannic acid and this effect was inhibited in the presence of PEG. Nevertheless, after 36 h incubation, it was found a significant increase in gas production in C + TA + PEG and, at the end-point (96 h), there were no differences between C and treatments with tannins or with QUE + PEG. When these data were fitted to a sigmoidal model, the potential gas production was significantly higher in C + TA + PEG. The rate of degradation was lower for tannins treatments and the addition of PEG was not able to revert this effect. DM and OM disappearance, true digestibility and NH3-N and VFA concentrations were significantly reduced by the treatments with quebracho and tannic acid. This adverse effect was not observed in the presence of PEG.
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