Addition of several tannin extracts to modulate fermentation of barley meal under intensive ruminant feeding conditions simulated in vitro by incubating at pH 6.0–6.2.

The potential use of tannin extracts from quebracho (QCT), grape (GCT), chestnut (CHT) and oak (OHT) included at 10, 20 or 30 mg/g to modulate rumen fermentation of concentrates was studied in three 24-h in vitro incubation runs, with barley grain as reference substrate and simulating high concentrate feeding conditions by adjusting pH at 6.2. Incubation pH at 8 and 24 h ranged from 6.14 to 6.18 and from 5.94 to 6.00, respectively. Gas production from barley alone (CTL) was linearly reduced with CHT (P < 0.05 up to 6 h; P < 0.10 from 8 to 18 h), OHT (P < 0.05 up to 12 h; P < 0.10 from 18 h), GCT (P < 0.05 from 2 to 24 h) and QCT (P < 0.10 up to 6 h), but a quadratic trend (P < 0.10) was also detected on GCT. The effect of GCT was highest and that of CHT lowest. Similarly, dry matter disappearance after 24 h showed a linear decrease with all tannin sources (P < 0.05), being lower with GCT than with QCT and CHT (P < 0.05). All tannin sources linearly increased (P < 0.05) molar butyrate proportion from CTL, at the expense of propionate proportion in GCT (P < 0.01) and CHT (P < 0.10). Except for the linear effect of chestnut on barley fermentation, all sources already reached their maximum level of response at their first level of inclusion (10 mg/g), especially with GCT. Qualitatively, tannins did not largely affect pH or other environmental parameters, except for an increase in butyrate proportion. Ruminants given high-concentrate diets are at risk of acidosis. Use of tannin extracts as dietary additives may slow down the fermentation rate, thus reducing the pH drop. The magnitude of the effect depends on the type of tannin but is not related to its chemical classification. Effect on fermentation is not dose related. [ABSTRACT FROM AUTHOR]