Strategic use of tannins as means to limit methane emission from ruminant livestock

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Abstract

In two experiments, the effects of supplementing tannins via a tannin-rich legume or a tannin extract on methane emission were determined. In Experiment 1, applying the rumen simulation technique, the tannin-rich legume Calliandra calothyrsus and the low-tannin legume Cratylia argentea were supplemented alone or in combination with each other to a tropical grass diet. In Experiment 2, six growing lambs, receiving either temperate grass or grass–legume diets, were supplemented with 0 or 25 g of Acacia mearnsii tannins/kg dietary dry matter. In Experiment 1, different from supplementation with C. argentea to the grass, methane emission did not increase when C. calothyrsus was added to the grass-alone diet and decreased linearly when C. argentea was successively exchanged by C. calothyrsus in the legume supplement. However, this decrease was associated with a corresponding reduction in the feeding value of the mixed diets. By contrast, in Experiment 2, the supplementation of the tannin extract decreased methane release (kJ/MJ gross energy intake) by 13% on average without affecting body energy retention. These results suggest that particularly extracted tannins can be useful in mitigating methane emission without major losses in feeding value of the diet while very tannin-rich shrub legumes such as C. calothyrsus, despite being also effective in limiting methanogenesis, are restricted in their application due to the simultaneous depression of the feeding value of the diet.

Introduction

There are some indications that tannins in the diet might help to reduce ruminal methane production either when included in significant proportions in temperate forage legumes [1] or when supplemented as purified tannin extracts [2]. Similarly, previous own in vitro experiments [3] presented indirect evidence that tannins, prevalent in the tropical shrub legume Calliandra calothyrsus, might be responsible for the methane production to be lower than with an unsupplemented low-quality grass diet and especially than with diets supplemented with Arachis pintoi or Cratylia argentea (tropical legumes low in tannins). However, it is still unclear (i) whether the tannin supplementation either through tanniniferous legumes or via tannin extracts is really effective in methane mitigation and (ii) to which extent this is associated with seriously adverse effects in terms of feeding value of the complete diet. These aspects were tested in two experiments, one of them with sheep using the respiratory chamber technique.

Section snippets

Materials and methods

In Experiment 1, the test diets consisted either of a tropical grass fed alone (Brachiaria humidicola) or of combinations of this grass with three different legume supplements. These made up 1/3 of dietary dry matter (DM) and were composed either of C. argentea alone, C. calothyrsus alone, or a 1:1 mixture of both legumes. The four diets were evaluated with the rumen simulation technique (Rusitec) [4]. Briefly, fermenters were filled with 890 mL strained rumen fluid obtained from a

Results and discussion

In Experiment 1, ammonia concentration in the fermenter fluid was increased (P < 0.05) by supplementation with C. argentea alone or in mixture with C. calothyrsus, but was not affected (P > 0.05) by supplementation with C. calothyrsus alone (see Table 1). Ammonia concentration decreased linearly (P < 0.001) and quadratically (P < 0.05) with increasing C. calothyrsus proportion in the legume supplement. Total volatile fatty acid (VFA) concentration increased (P < 0.05) with any type of supplementation

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    Supplements such as tannins are also known to have the potential to reduce emissions. Tannins are able to displace the nitrogen excretion from urine to feces to produce an overall reduction in emissions (Dickie et al., 2014; Hess et al., 2006). Fertilizer application on animal feed crops increases nitrous oxide emissions (Bouwman, 1996).

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