LAUSR

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.