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Khí methane gây Global warming do thú nhai lại

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Introduction
Methane gas causes global climate change 23 times more aggressive than CO2. It is produced not only in nature but also in human activities. In agriculture, methane is emitted by animal production and manure management, rice cultivation. Ruminants are known as the mainly source produce methane as a by-product of their feed digestion. (www.fao.org/ag/againfo/resources/documents/brief_notes/BNlivest-enviro10.pdf) (http://www.eoearth.org/article/Methane). There are many methods used to prevent the emission of methane through livestock, particularly ruminants. Feeding is also one of the methods used. Secondary compounds in plants are mentioned in reducing methanogenesis such as tannins, saponins and essential oil (Wang et al., 1997 and Dean and Ritchie, 1987).
Tannins
Plants contain tannins mostly in the vacuoles or surface wax of the plants. In these parts, tannins do not influence plant metabolism, but they will become active when the cells die or breakdown. Tannins may help regulate the growth of those tissues that these compounds are found such as leaf tissues, bud tissues, seed tissues, root tissues and stem tissues (http://en.wikipedia.org/wiki/Tannins). Tannins are the second most large group of plant phenolics after lignin. They are divided into two groups “condensed tannins” and “hydrolysable tannins” are harmful to many organisms in the rumen of ruminants especially ciliate protozoa, fibre degrading microbes and methanogenic bacteria (Vinod Kumar et. al., 2008)
Base Unit:
Gallic Acid

Flavone

Class/Polymer: Hydrolyzable Tannins Condensed Tannins
(http://en.wikipedia.org/wiki/Tannins)
Some forages that contain condensed tannins are sainfoin (Onobrychis viciifolia), Sericea Lespedeza (Lespedeza cuneata), Lotus pedunculatus (lotus), and Lotus corniculatus (Birdsfoot trefoil). These tannins can help the rumen fermented effectively with moderate quantity (4 to 6% of the total) in the diets. Nevertheless, high ratio of tannins (6-12% DM) can reduce feed intake, digestive efficiency and animal productivity. (Suchitra Kanpukdee and Wanapat, 2007)
Widiawati Y., et al (2007) found that organic matter degraded, microbial cell and NH3 produced of Gliricida sepium were the highest (505 mg, 2676 g and 1.91 mmol/100 mL) followed by Leucaena leucocephala and Calliandra calothyrsus in vitro. However, among the three plants, the production of total gas and methane were lowest in Gliricidia treatment (0.192 mL and 0.07 mole per mg OM deraded, respectively), then Leucaena (0.249 mL and 0.097 mole per mg OM deraded) and Callliandra (0.196 mL and 0.126 mole per mg OM deraded). Therefore, they suggest using Gliricidia was more efficient as the dietary energy for the animals’ production compared to the two other plants (Fig. 1)
Figure 1. Estimation of methane (CH4) produced, which was obtained from the concentration of acetate, propionate and butyrate when Leucaena (●), Giricidia (■) and Calliandra (▲) were degraded during the 48 hours of incubation

(Widiawati Y., et al ,2007)
An in vitro experiment in goats was conducted by Babayemi O. J. et al, (2006) on tea leaf and spent tea leave contained condensed tannins and steroids. Spent tea leave enhanced more methanogenesis than tea leave.
In another study, with two experiments, the first experiment using the rumen simulation technique, the supplementation of the tannin-rich legume Calliandra calothyrsus and the low-tannin legume Cratylia argentea to a diet of tropical grass mixture decreased the methane emission but reduced the feeding value of this diet. By contrast, the second experiment conducted in six growing lambs consuming either temperate grass or grass–legume diets with 0 or 25 g of Acacia mearnsii tannin extracts/kg dietary dry matter showed that tannin extracts could reduce the release of methane (kJ/MJ gross energy intake) by 13% while didn’t decrease the body energy retention (Fig. 2) (Hess H.D., 2006)




Figure 2. Effect of supplementing tannins on methane emission of sheep fed different basal diets (Experiment 2)


(Hess H.D., 2006)
Saponins
Saponins are glycosides with high molecular weight. Some feeds and forage plants containing saponins such as Alfalfa (3-5%), Sapindus rarak, Sapindus mokorossi, Yucca schidigera (4%), Quillaja saponaria (10%), Acocia concinna, Emblica officinalis, Sesbania sesban, Enterolobium cyclocarpum and in fruits (Sapindus saponaria, Sapindus rarak) etc. can decrease 20-60 percent methane production on different substrate and reduce ammonia N and protozoal population. Saponins decreased the amount of acetate and increased propionate production. By reducing the number of protozoa, saponin reduces the transfer of the H availability to the methanogenic bacteria and therefore reduces methanogenesis. (Vinod Kumar et. al., 2008) (Suchitra Kanpukdee and Wanapat, 2007)
Hess H. D. et al, (2003) compared the effects of saponins in three tropical fruits Sapindus saponaria, Enterolobium cyclocarpum and Pithecellobium saman on rumen fermentation by using a rumen simulation technique (Rusitec). There were four diets tested with faunated and defaunated rumen fluid from a cow. The saponin in the diet of 100 mg/g of Sapindus saponaria (crude saponins, 120 mg/g) decreased (P<0.05) the number of protozoa (by 54%) and daily methane release (by 20%) compared to control (no tropical fruit), but didn’t affect the methanogen count. Meanwhile, the diets of 200 mg/g of E. cyclocarpum (crude saponins, 19 mg/g) and 200 mg/g of P. saman (crude saponins, 17 mg/g) increased by 14% methane release and were not different from the control diet, respectively. Methanogenesis was suppressed in defaunated fluid by 43% over four diets (P<0.05), and S. saponaria could reduce more methane in defaunated (29%) while only 14% methane could be decreased in faunated rumen fluid (14%). This study revealed that S. saponaria reduced ruminal methanogenesis effectively, but didn’t affect the depression of protozoal count.

According to Wei-lian Hu and et al., (2005), conducted the in vitro experiment to investigate the changes on ruminal fermentation by adding tea saponins (TS) at levels of 0, 2, 4, 6 and 8 mg in the mixture of corn meal and grass meal (1/1, w/w) in rumen fluid. They recorded gas production (GP) and methane concentration at 3, 6, 9, 12 and 24 h incubation. At 24 h incubation, tea saponin decreased methane concentration by 13, 22, 25 and 26% with levels 2, 4, 6 and 8 mg of TS, respectively.

A study on sheep conducted by Wang C. J. et al, (2009) compared the effects of flavomycin (250 mg/d), ropadiar from an oregano extract (250 mg/d), and saponin in the form of a Yucca schidigera extract (170 mg/d) on the methane emission in sheep. Saponin diet produced more volatile fatty acid, and decreased the methane production by approximately 3.3 g/kg compared to the control. NH3-N concentrations and the methane production were positively correlated. Therefore, saponin could reduce rumen methanogenesis in sheep. (Fig. 3)

Figure 3. Methane emission from sheep under the different additive treatments



(Wang C. J. et al, 2009)
Nevertheless, the experiment of Goel G. et al. (2008) showed a negative effect of saponins extracted from Carduus, Sesbania and Knautia leaves and fenugreek seeds on the methanogenesis. Although the saponins, in this case, decreased the number of protozoa by 10 to 39%, 78% of methanogen numbers was reduced by Sebania saponin and 20 to 60% of fungal population while they increased Fibrobacter succinogenes (21–45%) and Ruminococcus flavefaciens (23–40%).
Essential oil
An essential oil is also known as volatile or ethereal oils. It is extracted by distillation, expression, or solvent extraction. Essential oils are used in perfumes, cosmetics and bath products, for flavoring food and drink, and for scenting incense and household cleaning products. (http://en.wikipedia.org/wiki/Essential_oil)
The study of Beauchemin K. A. and McGinn S. M. (2006) revealed that essential oil supplementation didn’t change the methane emissions in growing beef cattle fed a diet consisted of 75% whole-crop barley silage, 19% steamrolled barley, and 6% supplement (DM basis) and also lowered the digestibilities of all nutrients.
Conclusion
Plant secondary compounds promise a good source in decreasing the methanogenesis in ruminants because they are easy to find in local plants and cheap. However, depending on the concentration and type of plants, this effect will be different.
 
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