Effect of replacing Para grass (Brachiaria mutica) with Paspalum grass (Paspalum atratum) on dry mater degradability and methane production

Nguyen Van Thu and Le Van Phong

College of Agriculture, Can Tho University, Vietnam
nvthu@ctu.edu.vn

Abstract

An in vitro rumen incubation was used to evaluate the effects on nutritive value of replacing Para gross with Paspalum grass at levels of 0, 25, 50 and 100% (DM basis).

Replacing Para grass with Paspalum grass resulted in linear increases in degradability of DM and OM with corresponding decreases in methane production.

The reduction in methane as substrate degradability was increased supports the conclusion that increasing the nutritive value of ruminant diets is one of the most effective ways of reducing methane emissions from the livestock sector.

Keywords: diets, global emissions, ruminant

Introduction

Brachiaria mutica is a species of grass known by the common names para grass, buffalo grass, Mauritius signal grass, pasto pare, malojilla, gramalote, parana, Carib grass, and Scotch grass. Despite its common name California grass, it does not occur in California; it is native to northern and central Africa and parts of the Middle East, where it is cultivated for fodder. It was introduced elsewhere and it is now cultivated throughout tropical regions of the world for this purpose. (https://en.wikipedia.org/wiki/Brachiaria_mutica)

The hypothesis that was tested in the present experiment was that Paspalum grass had a much greater potential than Para grass (Brachiaria mutica) as the basis of a feeding system for ruminant animals in the tropics.

Materials and methods

A complete randomized design with 4 treatments and 3 replicates was used to determine the gas production and methane emission in an in vitro incubation . The treatments were the rates of substitution of Para grass by Paspalum grass at levels of 0, 25, 50 and 100% (DM) basis).

The in vitro gas measurement

The Para and Paspalum grasses were harvested, chopped to about 1 cm of length, dried at 65°C for 24h, then ground through a 1mm seive. Representative samples (0.2g of DM) were put into 50ml glass syringes. Buffer solution and cattle rumen fluid were added, prior to filling each syringe with carbon dioxide following the method described by Menke et al (1979). The syringes were put in a water bath at 39^oC. Gas, CH ₄ and CO₂ volumes were recorded at intervals of 0, 3, 6, 9, 12, 24, 48 and 72 hours. CH₄ and CO₂ concentrations were measured using the “Biogas 5000 equipment” from Geotechnical Instruments (UK) Ltd, England. Unfermented solids at 24 hours were determined by filtering through two layers of cloth and drying at 105°C for 24 hours and ashing for 5 hours for determination of DM and OM. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined following procedures described by Van Soest et al (1991).

The grass samples used as substrates were analyzed for proximate chemical composition (AOAC 1990).

Statistical analysis

The experiment was analyzed using the general linear mode procedure of MINITAB (version 18).

Result and discussion

Chemical composition of feeds

Paspalum grass was higher in OM, CP and EE and lower in NDF and ADF, than Para grass (Table 1).

Production of gas and methane and degradability of DM and OM

Methane production decreased with a curved linear trend as the Para grass was replaced by Paspalum grass (Table 2; Figure 1). In contrast, the degradability of DM and OM increased with replacement of Para grass by Paspalum grass (Figure 2).

Figure 1. Methane production decreased with a curvilinear trend as Paspalum grass replaced Para grass	Figure 2. DM degradability increased with a curvilinear trend as Paspalum grass replaced Para grass

The overall effect was that as DM degradability increased, there was linear decrease in the production of methane (Figure 3).

Figure 3. Methane production decreased with a linear trend as the degradability of the substrate DM was increased

Discussion

It is hypothesized that the increase in DM and OM degradability, as Paspalum grass replaced Para grass, created conditions in the rumen (eg: increased availability of hydrogen, lower pH, reduced numbers of protozoa), that favour growth of bacteria that produce propionic acid. The consequences would then be reduced availability of hydrogen available for the reduction of carbon dioxide to methane. Such an outcome is supported by the very close negative relationship (R² 0.99) between the rate of rumen DM degradability and the production of methane (Figure 3).

The results of this experiment support the proposal that the strategy for reducing methane emissions from ruminant livestock should be based on improving diet quality rather than diet quantity.

Replacing para grass with paspalum grass is an example of such a strategy. Another example is feeding yeast-fermented rice (the byproduct of rice wine production) as a supplement to a diet of ensiled cassava root, urea and casava foliage fed to fattening cattle in Laos (Sangkhom et al 2017. The critical component of yeast’ fermented rice is the yeast cell wall hydrolysate which is rich in beta- glucan a specific energy source for bacteria that produce volatile fatty acids Sangkhom et al (2017).

Are the of such an approach can be seen in the reduction of methane brought about by supplementing the diet with yeast fermented rice.

The key role of propionic acid in the volatile fatty acids produced in the rumen and fermentation is thus a key factor determining the emission of methane.

Conclusions

• Replacing Para grass with Paspalum grass resulted in linear increases in degradability of DM and OM with corresponding decreases in methane production.
  
  
• The reduction in methane as substrate degradability was increased supports the strategy that increasing the nutritive value of ruminant diets is one of the most effective ways of reducing global emissions of methane from the livestock sector.

References

AOAC 1990 Official methods of analysis, 15th edition). Washington, DC, Volume 1: 69–90

Menke K H, Raab L, Salewski A, Steingass H, Fritz D and Schneider W 1979 The estimation of the digestibility and metabolizable energy content of ruminant feeding stuffs from the gas production when they are incubated with rumen liquor in vitro. J. agric. Sci., 93: 217-222

Minitab 2017 Minitab reference manual release 18.1. Minitab Inc, Sydney, Australia.

Sangkhom I, Preston T R, Leng R A, Ngoan L D and Phung L D 2017 Rice distillers’ byproduct improved growth performance and reduced enteric methane from “Yellow” cattle fed a fattening diet based on cassava root and foliage (Manihot esculenta Cranz). Livestock Research for Rural Development. Volume 29, Article #131. http://www.lrrd.org/lrrd29/7/sang29131.html

wikipedia https://en.wikipedia.org/wiki/Brachiaria_mutica