Effects of tannic acid and quebracho tannins on in vitro ruminal fermentation of wheat and corn grain

Abstract

Current understanding of the effect of moderate amounts of tannins on the utilization of protein contained in forages indicates beneficial effects when fed to ruminants. Nevertheless, there is little knowledge about the effects of tannins on the ruminal hydrolysis of starch-rich concentrates. Modulation of the hydrolysis of starch may reduce the occurrence of metabolic disorders, such as acidosis, in ruminants consuming high-grain diets. The effects of commercial tannic acid (hydrolysable tannins) and quebracho tannins (condensed tannins) (50 g kg −1 DM) on the in vitro fermentation of ground wheat and corn grains by mixed ruminal bacteria was examined. The architecture and chemical composition of wheat and corn endosperms might explain differences in fermentation rates, as well as in response to similar concentrations of tannins. Regardless of the source of tannin, microbial fermentation was inhibited in both grains, as demonstrated by a decline in gas production, DM disappearance, volatile fatty acids and ammonia production. However, these effects were more pronounced for wheat than corn grain, mostly during the initial stages of the incubation. Scanning electron microscopy revealed that both sources of tannins inhibited the microbial hydrolysis of the endosperm protein matrix. Tannins did not prevent bacterial attachment to starch granules, but starch hydrolysis was slowed indirectly as a result of a tannin-mediated reduction in the degradation of the surrounding protein matrix. Tannins are likely to be more effective at modulating the rate of starch digestion in grains that possess a readily degradable protein matrix.

Assessment of the effect of condensed (acacia and quebracho) and hydrolysable (chestnut and valonea) tannins on rumen fermentation and methane production in vitro

“…However, valonea treatment at 50 g kg −1 had no impact on final pH or total VFA concentration. Getachew et al and Martínez et al reported lower gas production and total VFA concentration when quebracho tannins were supplied at 50 g kg −1 DM in batch culture fermentation compared with the control. Salawu et al studied the effect of 50 g kg −1 quebracho tannins on in vitro gas production and total VFA concentration in leaves and stems of calliandra.…”

Comparative Digestive Physiology

“…The complexing ability of proanthocyanidins and other tannins makes them reactive with bacterial cell walls and extracellular enzymes (311, 314). This could be the basis for how they can reduce microbial fermentation (39, 181, 300, 432) and growth, alter microflora populations, and reduce attachment of fungi and bacteria to substrates (2).…”

Desactivación de taninos en grano húmedo de sorgo con polietilenglicol o urea

“…La menor concentración de AGV totales en el tratamiento T puede ser explicada por el efecto negativo que generan los taninos sobre la fermentación microbiana. Al agregar taninos condensados de quebracho a granos de trigo y de maíz se logra disminuir la fermentabilidad in vitro disminuyendo la producción de AGV totales (Martinez et al, 2006). Las concentraciones molares de acéti-co, butírico e iso-valérico no fueron modificadas por los tratamientos (p>0,05, tabla II).…”