Nutritional evaluation of plant species using the
water extraction technique

Miech Phalla

University of Tropical Agriculture, Cambodia
phalla@utafoundation.org
phalla@mekarn.org

Abstract

Thirteen samples of leaves of various tropical plant species available around An Giang University, Vietnam, were selected for determining dry matter and N content and water extractable DM and N as indicators of nutritive value. The leaf samples were dried by micro-wave radiation, ground in a coffee grinder and washed for 90 minutes in a semi-automatic washing machine.

The range of DM content was from 4.6 to 41.9%, and for N in DM from 1.7 to 5.8%. Water extractable DM ranged from 15.1 to 35.5% and water extractable N from 19.9 to 58.3%. The two water plants with high levels of crude protein in the leaf (Ipomoea and duckweed) had the highest amount of water extractable DM. Levels of water-extractable N were also high for these species. The plants with lowest values for water-extractable DM and N were bamboo, banana and Muntingia. There appeared to be a negative relationship between the DM content of the leaves and the proportion of the water-extractable N.

It is concluded that water extraction is a simple, low cost, and effective technique to indicate the nutritional value for monogastric animals of leaves from trees and water plants.

Key words: Dry matter, nitrogen, nutritive value, plants, water extraction

Introduction

There are many kinds of plant species that are used for animal feed, derived from local resources but research has concentrated on very few of these (Rosales and Gill 1997). These authors emphasised the need to make greater use of the diversity of fodder tree species as providers of animal forage. More than 200 species of trees fix N and are reported to be useful as fodder species (Brewbaker 1986). The use of protein-rich feeds like leaves from trees can improve the nutritive value of  low quality crop residues  such as rice straw (Ho Quang Do et al 2001; Mom Seng et al 2001).

The technique of measuring washing losses to estimate the nutrient values of feeds has been proposed for both ruminants (Huntington and Givens 1997) and non-ruminants (Hyslop et al 1999). The method was further developed by Ly and Preston (1997) so as to standardise the procedure, and it was shown that there was a good relationship between this procedure and the conventional in vitro methods based on gas production and pesin-pancreatin digestion (Ly and Preston 2001).

The purpose of the research reported in this paper was to use the water extraction technique to evaluate a range of plant species available in the area around An Giang University, and to compare the results with standard values in the literature.
 

Materials and methods

Sample collection

Samples of foliage were obtained in the morning (about 9.00am) from a wide range of trees, shrubs, grasses and water plants in the area around An Giang University (Table 1).  In the case of the trees, the leaves were from the ends of branches which were about 0.5 m in length. The foliage was separated into leaves, petioles and stems, which were weighed on fresh basis. The names of the plants that were sampled are in  materials were shown in Table 1.

Procedure

The procedure was described by Ly and Preston (1997). Washing losses (WL) were determined in triplicate samples of each of the leaves and also from the stems for the water spinach. The samples were dried in a fixed temperature oven (60ºC) for 24 hours and then in a micro-wave oven to make sure the samples were completely dry to constant weight. They were then ground in a coffee mill. A sample (about 1 g) of the dry ground material was put into weighed nylon bags, size 50 x 150 mm, with a pore size of 45 to 55µ. The bags containing the samples were tied and put into the washing machine with 3 liters of water per bag. Washing took place for 90 minutes with 10 minutes in each cycle. After washing, the bags were dried and weighed and N determined on the dry residue.

Chemical analyses

Samples of each component were analyzed for DM in duplicate by the micro-wave radiation method of Undersander et al (1993). N in the leaves and in the dry residue after washing was determined by the method of AOAC (1990).

Statistical analysis

The data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) option of the MINITAB software (Release 13.31). Sources of variation were the species and error.
 

Results and discussion

Proportions

The proportions of leaves (fresh basis) ranged from 33% for Ipomoea to 67% in the banana plant (Table 2)

Dry matter and Nitrogen

As was to be expected there was a wide range in the dry matter content of the leaves and in the nitrogen (and crude protein) in the leaf dry matter (Table 3 and Figures 1 and 2). Duckweed had the lowest content of dry matter followed by the other water plants (Ipomoea aquatica and water hyacinth).  Highest leaf DM content was in Bamboo. The order for N content of the leaves tended to be the opposite of that for DM, but this was not a consistent relationship; N concentrations were highest in duckweed followed by the leucaena leaflets and cassava leaves. Lowest values were in Jackfruit leaves.

 

Figure 1: Dry matter content of the leaves of a range of plant species	Figure 2: Crude protein content of the leaves of a range of plant species

Water extractable DM and N

 

Figure 3: Water extractable dry matter in the leaves of a range of plant species	Figure 4: Water extractable nitrogen in the leaves of a range of plant species

There appeared to be a negative relationship between the DM content of the leaves and the proportion of the water-extractable N (Figure 5).

Figure 5: Relationship between water extractable N and the DM content of the leaves

Values for water-extractable N in this study are compared in Figure 6 with those reported by Ly and Preston (2001). While the trends are similar for both sets of data, and there is good agreement for certain plant species (eg: banana, cassava, Ipomoea and duckweed), there are major  discrepancies for others (eg: Leucaena and Jackfruit).  The implication is that the method is still not sufficiently well standardised and that the differences between results from different researchers probably reflect differences in the preparation of the samples and the origin of the leaves. In this connection, major differences in the in vivo digestibility of young and old cassava leaves were reported by (Chhayty et al 2003); while Ngo Thuy Bao Tran (2003) encountered consistent differences in the DM, N, and water-extractable DM and N in leaves taken from the top compared with those from the bottom of a range of trees. DM percentage was lower and N and water-extractable DM and N levels were higher in the leaves taken from the top of the trees.

Figure 6: Comparison of the values for water extractable dry matter with those
reported by Ly and Preston (2001)

Chermiti et al (1996) suggested that washing loss of DM from fibrous feeds represented the detergent soluble substances, or cell contents. Thus water extractable DM and N could be reasonable indicators of the digestibility of fibrous feeds for monogastric animals.

Conclusion

It is concluded that water extraction is a simple, low cost, and effective technique to indicate the nutritional value for monogastric animals of leaves from trees and water plants.
 

Acknowledgments

I wish to thank the MEKARN programme for providing me the opportunity to conduct this mini-project in order to improve and develop my knowledge; and Dr Preston, Dr Ly and MSc Chhay Ty for advice and assistance in interpreting the data.

Reference

AOAC 1990: Official Methods of Analysis. Association of Official Analytical Chemists. 15^th edition (K Helrick editor) Arlingtonpp 1230

Brewbaker J L 1986: Leguminous trees and shrubs for Southeast Asiaand the South Pacific. In: Forages in Southeast Asiaand South Pacific Agriculture (G J Blair, D A Ivory and T R Evans, editors) Australian Centre for Internatinal Agricultural Research Proceedings Series No. 12 Camberra p 43-50

Chhay Ty,  Preston T R and Ly J  2003:  The use of ensiled cassava leaves in diets for growing pigs. 2. The influence of type of palm oil and cassava leaf maturity on digestibility and N balance for growing pigs.  Livestock Research for Rural Development (15)8 Retrieved September 25, 2003, from http://www.cipav.org.co/lrrd/lrrd15/8/chha158.htm

Chermiti A, Nefsaoui A, Teller E, Vanbelle M, Ferchichi H and Rakbani N 1996: Prediction of the voluntary intake of low quality roughages by sheep from chemical composition and ruminal degradation characteristics. Animal Science, 62:57-62

Ho Quang Do, VoVan Son, Do Vo Anh Koa and Nguyen Tim Kim Khang 1999: Urea supplementation of rice straw for Sindhi x Yellow cattle, sprayed in solution, as a soft cake or hard block. Livestock Research for Rural Development vol.11 (2)

Huntington J A and Givens D I 1997: Studies on in situ degradation of feeds in the rumen.1. Effect of species, bag mobility and incubation sequence on dry matter disappearance. Animal Feed Science and Technology 64:227-241

Hyslop J J, Stefandottir G J, McLean B M L, Longland A C and Cuddeford D 1999: In situ incubation sequence and its effect on degradation of food componentswen measured in the caecum of ponies. Animal Science 69:147-156

Ly J and Preston T R 1997: An approach to the estimation of washing losses in leaves of tropical trees. Livestock Research for Rural Development 9(3): http://www.cipav.org.co/lrrd/lrrd9/3/ly931.htm

Ly J and Preston T R 2001 In vitro estimates of nitrogen digestibility for pigs and water-soluble nitrogen are correlated in tropical forage feeds.  Livestock Research for Rural Development 13(1): http://www.cipav.org.co/lrrd/lrrd13/1/ly131.htm

Mom Seng, Preston T R, Leng R A  and ter Meulen U 2001:  Effect of a single drench of cooking oil on the rumen ecosystem and performance of young local "yellow" cattle fed rice straw and cassava foliage.  Livestock Research for Rural Development 13(4): http://www.cipav.org.co/lrrd/lrrd13/4/ly134.htm

Ngo Thuy Bao Tran 2003: Effect of age of leaves from forage trees on nutritive value.  Retrieved September 25, 2003, from MEKARN Mini-projects. http://www.mekarn.org/MSc 2003-05/miniprojects/tran.htm

Undersander D, Mertens D Rand Theix N 1993 Forage analysis procedures. National Forage Testing Association. Omaha pp 154

Go to top