Difference in the nature of tannins on in vitro ruminal methane and volatile fatty acid production and on methanogenic archaea and protozoal populations

Abstract

Six plant sources of hydrolyzable tannins (HT) or HT and condensed tannins (CT; designated as HT1, HT2, HT3, HT + CT1, HT + CT2, and HT + CT3) were evaluated to determine their effects in vitro on CH(4) production and on ruminal archaeal and protozoa populations, and to assess potential differences in biological activities between sources containing HT only or HT and CT. Samples HT1, HT2, and HT3 contained only HT, whereas samples HT + CT1, HT + CT2, and HT + CT3 contained HT and CT. In experiment 1, in vitro incubations with samples containing HT or HT + CT resulted in a decrease in CH(4) production of 0.6 and 5.5%, respectively, compared with that produced by incubations containing the added tannin binder polyethylene glycol-6000. Tannin also suppressed the population of methanogenic archaea in all incubations except those with HT2, with an average decrease of 11.6% in HT incubations (15.8, 7.09, and 12.0 in HT1, HT2, and HT3) and 28.6% in incubations containing HT + CT (35.0, 40.1, and 10.8 in HT + CT1, HT + CT2, and HT + CT3) when compared with incubations containing added polyethylene glycol-6000. The mean decrease in protozoal counts was 12.3% in HT and 36.2% in HT + CT incubations. Tannins increased in vitro pH, reduced total VFA concentrations, increased propionate concentrations, and decreased concentrations of iso-acids. In experiment 2, when a basal diet was incubated with graded levels of HT + CT1, HT + CT2, and HT + CT3, the total gas and CH4 production and archaeal and protozoal populations decreased as the concentration of tannins increased. Our results confirm that tannins suppress methanogenesis by reducing methanogenic populations in the rumen either directly or by reducing the protozoal population, thereby reducing methanogens symbiotically associated with the protozoal population. In addition, tannin sources containing both HT and CT were more potent in suppressing methanogenesis than those containing only HT.

In vitroindications for favourable non-additive effects on ruminal methane mitigation between high-phenolic and high-quality forages

“…Various investigations are currently under way to identify and test means for mitigating CH 4 emissions that originate from ruminants due to the activity of methanogenic archaea during feed fermentation (1) . As a product of fermentative digestion, CH 4 emission levels depend considerably on the quantity and composition of feeds consumed (2) .…”

“…As a product of fermentative digestion, CH 4 emission levels depend considerably on the quantity and composition of feeds consumed (2) . The potential of mitigating CH 4 emissions by the extracts of phenolic compounds, which are synthesised in the intermediary metabolism of plants, has been demonstrated experimentally (3 -5) . Also, the direct inclusion of plants containing phenolics in ruminant diets reduced CH 4 emissions compared with control diets, both in vitro (6) and in vivo (7,8) .…”

“…A major drawback in implementing diets with doses of phenolics aimed at reducing CH 4 emissions is often a decline in the digestibility of the feed and therewith the productivity of the animals (9) , even at dosages where toxic side effects are excluded. As a consequence, there are often no or only small declines in CH 4 per unit of digested feed and, therefore, food produced.…”

“…As a consequence, there are often no or only small declines in CH 4 per unit of digested feed and, therefore, food produced. Analysing a larger dataset by principal components analysis illustrated that plants with high forage quality are arranged opposite to those with a high CH 4 mitigating potential (10) . This indicates that achieving both goals simultaneously is difficult.…”

“…This indicates that achieving both goals simultaneously is difficult. Studies by Tiemann et al (8,11) , where low-quality tropical Brachiaria hay was combined with highly tanniferous shrub forage, have shown that any reduction in CH 4 was associated with a correspondingly lower utilisation of dietary energy. This may be different when high-phenolic plants are combined with high-quality feeds.…”