Livestock Research for Rural Development 30 (6) 2018 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Effects of some essential oils on methane production in an in vitro rumen fermentation of vetch-oat hay

H Bouchiha, S Malouk1, K Bouchama2 and A Acidi3

Department of Biology, El-Tarf University, Algeria
b_hananedz@yahoo.fr
1 Department of Biology, Ghérdaya University, Algeria
2 Department of Biology, Khenchla University, Algeria
3 Department of Biology, Annaba University, Algeria

Abstract

This study was conducted to evaluate the effect of essential oils of Lavandula dentata and Mentha piperita plants on gas and methane production in an in vitro rumen incubation using rumen liquor obtained from three slaughtered sheep. The mixture of rumen fluid with buffer 1:2 v/v, was placed in 100ml syringes containing 200mg of the substrate. The incubation procedure was repeated three times. The gas production and concentration of methane were recorded after 24h of incubation.

Gas production after 24 h incubation declined with a linear trend as the concentration of the essential oils in the substrate was increased in the range zero to 95µl/g of the vetch-oat hay, the rate of decrease apparently being greater for Mentha piperita than for Lavandula dentata.

The concentration of methane in the gas declined with curvilinear trends, the effect appearing to be more marked in the case of Metha piperita. However, there were no overall differences between the two sources of essential oil. The pH in the in vitro system was increased by addition of essential oils but the magnitude of the increase was very small. The pH did not differ between the two sources of oil. The potential for reducing methane production by adding the two sources of essential oils tested in this experiment must be viewed against the associated reduction in gas production, and the overall effects in the intact ruminant animal.

Key words: methane, ruminants, greenhouse, essential oil, Lavandula dentate, Mentha piperita, digestibility


Introduction

Methane production in ruminants has received global attention in relation to its contribution to the greenhouse gas effect and global warming. Many researchers have explored a variety of approaches as a means of decreasing methane production in ruminants. Some approaches, such as feeding of antibiotics (bacteriophages, bacteriocins) and chemical inhibitors, directly target methanogens but the public concern over use of antibiotics in livestock production has increased in recent years because of their possible contribution to emergence of antibiotic resistant bacteria and their transmission from livestock to humans. Other approaches, such as defaunation and promotion of acetogenic populations, seek to lower the supply of metabolic hydrogen to methanogens. Most additives of this type tend to be eliminated due to safety concerns in animal-derived food (Castillijos et al 2006).

Characterization of microbial activity and methane production in the rumen may provide insights for development of effective strategies for reducing methane emissions from ruminants. Essential oils are naturally occurring volatile extracts of plants responsible for giving spices their characteristic essence and color; they also have antimicrobial properties (Newbold et al 2004) that make them potential alternatives to antibiotics to manipulate the microbial activity in the rumen (Spanghero et al 2008).

This study focuses on exploring the capacity of two essential oils (EO), extracted from lavender (Lavandula dentata) and menthe (Mentha piperita)) to reduce methane production and enhance degradability of vetch-oat hay in an in vitro fermentation.


Materials and methods

Essential oils

The aerial parts of the two plants (Lavandula dentata and Mentha piperita) were collected during May 2007 by hand cutting. Extraction of the essential oil was made by the hydro-distillation process (100 g of the plant was mixed with 700ml of distilled water). The oils were collected by condensing and then separating the oil by settling. The oils were stored in dark bottles at 4°C.

In vitro rumen system

The in vitro system was prepared following the procedure of (Menke et al 1979). Rumen liquor taken at random from 3 slaughtered sheep was mixed with artificial saliva (1: 2 v/v). The latter was prepared as described by Menke et al (1979). The syringes (100ml), prewarmed at 39°C, contained 200 mg (DM basis) of substrate (vetch-oat hay). They were inoculated with 30 ml of rumen fluid under continuous CO2 reflux and incubated at 39°C for 24 h. The oils were injected into the syringes just before the incubation. The levels were 10, 14 and 19 µl. In each test, three syringes with control substrate (blank) were also incubated but without additive (syringes incubated with the inoculum alone).

Cumulative gas production was assessed  after 24h. The content of methane in the gas was measured by injection in each syringe of 4 ml of sodium hydroxide (NaOH, 10N) (Bouchiha et al 2015). The gas production in the blanks (syringes incubated with the inoculum alone) was subtracted from the gas production in syringes incubated with the inoculum and substrate, to get net gas production values.

Statistical analysis

The data were analyzed by ANOVA employing the SAS (1990) software. Polynomial regression equations were fitted to the data relating gas production and methane content in the gas (Y) with the level of oil level added to the substrate (X).


Results and discussion

The pH in the in vitro system was increased by addition of the essential oils in the range zero to 95µl/g of the vetch-oat hay but the differences were very small (Table 1). There were no differences in pH due to the source of oil.

Gas production after 24 h incubation declined with a linear trend as the level of oil was increased (Figure 1). The rate of decrease was greater for Mentha piperita than for Lavandula dentata.

The concentration of methane in the gas declined with curvilinear trends with increasing level of oil in the substrate, the effect appearing to be more marked in the case of Metha piperita (Figure 2). However, over the range of oil concentrations that were studied there were no overall differences between the two oils (Table 1).

Table 1. Mean values for pH, gas production at 24h and content of methane in the gas according to addition of essential oils (Lavandula dentata and Mentha piperita)

Gas, ml

Methane, %

pH

Oil, Ál/200mg substrate

0

34.7

17.3

6.623

10

31.2

16.3

6.678

14

29.7

14.7

6.703

19

28.8

13.2

6.705

SEM

0.056

0.25

0.013

p

<0.001

<0.001

<0.001

Source of oil

Lavendula

32.3

15.3

6.68

Mentha

29.8

15.5

6.68

SEM

0.4

0.25

0.0091

p

<0.001

0.4

0.70



Figure 1. Effect of addition of essential oils from Lavandula dentata and Mentha piperita
on gas production from 200 mg of vetch-oat hay after 24h fermentation
Figure 2. Effect of addition of essential oils from Lavandula dentata and Mentha piperita
on methane content of the gas after 24h incubation of 200 mg of vetch-oat hay

The potential for reducing rumen methane production by adding essential oils must be viewed against the associated reduction in rumen gas production (a relationship which has been shown in other in vitro rumen studies (eg: Ataly et al 2018). However, gas production in the rumen only measures the events in that part of the digestive tract. Feed biomass that is not fermented in the rumen has the potential to contribute amino acids to the animal if it is rich in “bypass” protein, while the “energy-rich” component can yield volatile fatty acids when fermented in the cecum-colon – a process which yields metabolizable energy excluding methane production and without carbon dioxide (Demeyer 1991; Immig 1996; Popova et al 2013; Leng 2018, in press). It is essential that corollary experiments are done to relate effects in the rumen with those in the intact animal.


Conclusions


References

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Received 31 December 2017; Accepted 6 May 2018; Published 1 June 2018

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