Chemical composition, nutritive value and rumen methane potential of some legume tree pods

A I Atalay, C O Ozkan¹, E Kaya¹, A Kamalak¹ and O Canbolat²

Department of Animal Science, Faculty of Agriculture, University of Igdır, Igdır, Turkey
¹ Department of Animal Science, Faculty of Agriculture, University of Kahramanmaras Sutcu Imam, Kahramanmaras, Turkey
akamalak@ksu.edu.tr
² Department of Animal Science, Faculty of Agriculture, University of Uludag, Bursa, Turkey

Abstract

The aim of the experiment was to determine the chemical composition, in vitro gas and methane production and rumen degradable substrate of pods from five leguminous tree species (Leucaena leucocephala, Albiza julibrissin, Robinia pseudoacacia, Acacia karroo and Gleditsia triacanthos) fed to small ruminant animals in Turkey.

The pods had adequate levels of crude protein (13-21% in DM), high levels of water soluble DM (30-50% in DM) and moderate levels of NDF (33-51% in DM). Concentrations of condensed tannin were relatively low (0.56-4.3% in DM) except for Gleditsia triacanthos (7.99%). In anin vitro rumen incubation, there was a close relationship (R ²=0.75)) between level of condensed tannin in the pods and methane concentration in the gas for four of the five species. Gleditsia triacanthos with the highest level of condensed tannin (8.0%) and the highest level of methane in the gas (6.2%) did not fit this relationship; the high content of sugars reported for this species may have been the factor contributing to the atypical relationship between the condensed tannin content and methane production. Methane content of the gas was linearly related with rate of gas production (R²=0.91, dry matter mineralized over the 24 h incubation (R²=0.97) and with the content of waCer soluble dry matter in the pods (R²=0.99). The NDF content in the pods was a less reliable measure of methane production (R²=0.78).

Key words: condensed tannin, gas production, in vitro fermentation, water-soluble dry matter

Introduction

Legume trees provide considerable amount of biomass from leaves and pods for ruminant animals to meet the requirement during the critical periods of the year (Kamalak 2006; Ngwa et al 2011; Canbolat 2012; Kamalak et al 2012; Kaya and Kamalak 2012). Research on chemical composition in combination with in vitro gas production technique can help to evaluate the potential nutritive value of previously un-investigated alternative feed sources (Karabulut et al 2006; Karabulut et al 2007; Kamalak et al 2011; Canbolat 2012; Guven 2012; Kaya and Kamalak 2012). The aim of the current experiment was to determine chemical composition, rumen gas and methane production of pods used to feed small ruminants in Turkey.

Materials and Methods

Legume tree pods

Pods from Leucaena leucocephala, Albiza julibrissin, Robinia pseudoacacia, Acacia karroo and Gleditsia triacanthos were collected in November 2015 from at least 10 different trees in the south of Turkey. The pods were ground using a laboratory mill with 1 mm screen size. Dry matter (DM) was determined by drying the samples at 105^oC overnight and ash by igniting the samples in a muffle furnace at 525^oC for 8 h. Nitrogen and ether extract content was determined according to AOAC (1990). Cell wall contents (NDF and ADF) were determined by the method of Van Soest et al (1991) and condensed tannin by the butanol-HCl method (Makkar et al 1995). The water-soluble DM content was determined by the method described by Ly and Preston (1997). Approximately 2 g of ground pod samples were put into nylon bags (45-55 micron pore size; 6.5-13 cm diameter) and washed for 25 min with water in a domestic washing machine.

In vitrogas and methane production

Samples (200 mg DM) were incubated with buffered rumen fluid for 24 h in glass syringes (100ml capacity) in a water bath at 39 ^oC using the method of Menke et al (1979). Rumen fluid was obtained from three rumen-fistulated sheep fed alfalfa hay (60 %) and barley grain (40 %). Gas production was determined after 24 h incubation. Methane in the gas was determined by passing samples through an infra-red methane analyzer (Sensor Europe GmbH, Erkrath, Germany) (Goel et al 2008). At the end of the 24 h incubation the contents of the syringes were transferred into a beaker with 50 ml of NDF solution and refluxed for 1 h. The residue was filtered through pre-weighed sintered glass crucibles to determine the dry matter mineralized.

Statistical analysis

One-way analysis of variance (ANOVA) was used to determine the effect of species on recorded variables (SPSS, 19). Differences among means were identified using Tukey’s multiple range test.

Results and discussion

Chemical composition of legume tree pods

In all species, the crude protein content was higher than the minimum requirement for optimum rumen function and feed intake (Preston and Leng 1987). Condensed tannins were in the range favored for rumen escape of protein (Barry et al 1984) with the exception of Gleditsia triacanthos where the level was 7.99% in DM. The pods of this species had the highest concentration of water-soluble DM (50%), which is in agreement with the reported 29.2% of sugars in pods of this species (Bruno-Soares and Abreu 2003). These authors reported lower values for condensed tannins (5.4% in DM in pods from trees in Portugal. Differences in climate may be the reason for these differences in pod composition.

Effect of species on in vitro gas and methane production of legume tree pods

Lopez et al (2010) suggested that the methane percentage in the gas produced after 24 h rumen fermentation can be used to classify the methane reduction potential of a feed as: low (11-14% methane), moderate (6-11% methane) and high (<6% methane). According to this classification all the species studied could be rated as having “high methane reduction potential” (Table 2).

Condensed tannins and methane production

Gas and methane production are reported to be negatively correlated with condensed tannin content of diets (Singleton 1981; Silanikove et al 1996). Waghorn 2008). This was also the case in the present experiment when the data for Gleditsia triacanthos pods (7.99% condensed tannin; 6% methane in the gas) were excluded from the analysis (Figure 1). Gleditsia triacanthos pods had the highest values for water soluble DM and for DM mineralized after 24h fermentation (Table 2). These results are in line with reports of 22% soluble sugars in the pods of this species ( Bruno-Soaroes and Abreu 2003). It is possible that the high content of soluble sugars in the Gleditsia triacanthos pods were the reason for the high gas and methane production in this species as soluble sugars do not bind with tannins.

Figure 1. Relationship between condensed tannin (CT) in the pods and methane content in the gas (excluding values for Gleditsia triacanthos)

Relationships between rumen fermentability and methane production

There were very close correlations between the methane content in the gas and: (i) gas production (Figure 2), (ii) water soluble dry matter in the substrate (Figure 3), and (iii) substrate DM mineralized in 24 h (Figure 4). All these criteria of fermentability were reliable predictors of methane production.

Figure 2. Relationship between gas production in 24h and methane content of the gas	Figure 3. Relationship between substrate DM mineralized in 24h and methane content of the gas

Water soluble dry matter was a better predictor of methane production than NDF (Figures 4 and 5).

Figure 4. Relationship between water-soluble dry matter in the substrate and methane content of the gas	Figure 5. Relationship between NDF in the substrate and methane content of the gas

Water-soluble DM as indicator of rumen degradability

Determination of water-soluble dry matter is a simple procedure and the values obtained correlate well with other indicators of rumen degradability (Figures 6 and 7).

Figure 6. Relationship between water-soluble DM in the substrate and DM mineralized in 24h	Figure 7. Relationship between water-soluble DM in the substrate and gas production in 24h

Conclusions

• The pods of the five tree species (Leucaena leucocephala,Albiza julibrissin, Robinia pseudoacacia, Acacia karroo and Gleditsia triacanthos) all had adequate levels of crude protein for efficient rumen function. Concentrations of condensed tannin were relatively low (0.56-4.3% in DM) except for Gleditsia triacanthos (7.99%).
  
  
• In an in vitro rumen incubation, there was a close correlation (R²=0.75)) between level of condensed tannin in the pods and methane concentration in the gas for four of the five species.Gleditsia triacanthos with the highest level of condensed tannin (7.99%) and the highest level of methane in the gas (6.2%) did not fit this relationship; the high content of sugars reported for this species may have been the factor contributing to the atypical relationship between the condensed tannin content and methane production.
  
  
• Methane content of the gas was linearly related with rate of gas production (R²=0.91), dry matter mineralized over the 24 h incubation (R²=0.97) and with the content of water soluble dry matter in the pods (R²=0.99). The NDF content in the pods was a less reliable measure of methane production (R²=0.78).

Acknowledgements

The authors would like to thank Dr T R Preston for invaluable contribution during writing of the manuscript.

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Received 22 May 2017; Accepted 21 April 2018; Published 1 May 2018

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