Effect of age of leaves from forage trees on nutritive value

Ngo Thuy Bao Tran

An Giang University, Vietnam
ntbtrancnty@yahoo.com

Abstract

The objective of this experiment was to obtain information on the relative nutritive value of young versus old leaves taken from trees considered to be suitable for feeding to livestock. Measurements were made of dry matter, nitrogen and the water extractability of DM (WEDM) and N (WEN) in ten trees: Banana, Cassava, Hibiscus rosa-sinuensi, Trichanthera gigantea, Ceiba, Samanea saman, Nauclea, Mango, Largesroemia, and Muntingia calabura.

All the above indices of nutritive value were better for young than for old leaves.

The higher content of N and of WEDM and WEN in young versus old leaves in a wide range of trees indicates that live stock should have better performance traits when they are fed young rather than old leaves. The water-extractable N may be indicative of the relative suitability of the leaves as feeds for monogastric animals (high WEN) and ruminants (low WEN).

Key words:  Banana, Cassava, Hibiscus rosa-sinuensi, Trichanthera gigantea, Ceiba, Samanea saman, Nauclea, Mango, Largesroemia, Muntingia calabura, nutrition, water extract
 

Introduction

Live stock play an important role in the farming system as they provide meat and milk for humans, income for farmers and manure for cropping. Nowadays, the rapid increase in population together with the economic development in Vietnam has led to an increase in demand for food generally, and animal protein in particular. So development of live stock production systems is one of the Government strategies. The traditional feeding system for livestock is based on locally available feed resources such as rice straw, rice bran, sugar cane tops, sweet potato vine, cassava root meal and agro-industrial by-products with the use of commercial feed as a supplement. Green plants are used as traditional feeds in diets for animal in Mekong delta, but very little is known about their nutritive value and especially protein availability.

Farmer  in the Mekong delta that grow Trichanthera gigantea select the young leaves rather than the old ones for feeding to their animals (Nguyen Thi Hong Nhan, personal communication). Their belief that the  "new" leaves on the Trichanthera gigantea tree have higher nutritive value than older leaves is supported by research in Cambodia (Chhayty et al 2003), in which cassava leaves from young re-growths (about 2 months old) had higher digestibility for pigs than leaves from plants grown for root production and which were 5 months old when the leaves were harvested.

The main aim of the present experiment was to study the nutritive value of young and old leaves from a range of trees found in the Mekong delta.

Materials and methods

Study sites

The leaves were collected from trees located around Long Xuyen and Can Tho city. The experiment was carried out in the laboratory of the Faculty of Agriculture and Natural Resources of An Giang University, in Long Xuyen City, Vietnam.

Sample collection

Samples were taken of leaves from the top and from the bottom of the following trees: Cassava, Hibiscus rosa-sinuensi, Banana, Trichanthera gigantea, Ceiba, Samanea saman, Nauclea, Mango, Largesroemia and Muntingia calabura. It was assumed that the leaves at the top of the trees or shrubs are the young leaves and that the leaves at the bottoms are the old leaves. Plant samples were collected in the morning and immediately put into plastic bags to avoid moisture losses and brought to the laboratory in the same day.

Chemical: analysis

Duplicate samples were analysed for dry matter (DM), crude protein (CP) and water-extractable DM and N. The dry matter content was determined by drying to constant weight in a forced draught oven. Nitrogen was measured by the Kjeldahl technique according to the AOAC (1990) procedure. The water extractable DM and N were determined by the methods described by Ly and Preston (2001).

Statistic analysis

The data were subjected to analysis of variance (ANOVA) using the General Linear Model of the Minitab software (version 13.3). Sources of variation were: trees, position in tree and error.

Results and discussion

Young leaves had lower content of DM and higher concentrations of N and water-extractable DM and N, than old leaves (Table 1 and Figures 1, 2, 3 and 4). The differences in favour of young leaves were consistent for all the trees, with two exceptions (Hibiscus and Lagerstroemia)  in the case of the water-extractable N; however, the magnitude of the difference varied among the trees.

Figure 1: Dry matter content of young and old leaves in a range of trees

Figure 2: Water extractable DM in young and old leaves in a range of trees

Figure 3: Nitrogen content in young and old leaves from a range of trees

 

Figure 4: Water-extractable N in young and old leaves from a range of trees

The results of this experiment indicate that young leaves will be better sources of digestible nutrients than old leaves taken from the same tree.  These findings support the observations of Nguyen Thi Hong Nhan (personal communication) concerning farmer practices on use of Trichanthera foliage in the Mekong delta (the farmers select the young leaves for feeding to their live stock) and of Chhayty et al (2003) in  Cambodia where young leaves from cassava regrowth were more digestible for pigs than old leaves taken at the time of root harvest.

 As plant tissue matures the proportion of cell wall increases while cell content is reduced and, within both the cell wall and cell content, there are changes in chemical composition (Oboe 1980). The stage of growth at the time of cutting is the most important crop factor determining the nutritive value of the conserved product. The later the date of cutting the larger will be the yield, the lower the digestibility and the lower the voluntary intake of dry matter by animals (McDonald et al 1995)

The fact that the water-extractable DM and N were lower in the young compared to old leaves of cassava, is in accordance with the report by Ravindran and Ravindran (1988) that with maturity, the fibrous fraction of cassava leaves changes it structure and composition. The superior nutritive value of young rather than old cassava leaves could be due to the effect of possible changes in the linkage of nutrients to the fibre fractions. In this respect, it may be that high values for water-extractable N is indicative of the suitability of such leaves / plant species as feeds for monogastric animals while low values could imply they should be fed to ruminants.

Conclusion

• The higher content of N and of water-extractable DM and N in young versus old leaves in a wide range of trees indicates that live stock will have better performance traits when they are fed young rather than old leaves.
• The water-extractable N may be indicative of the relative suitability of the leaves as feeds for monogastric animals (high WEN) and ruminants (low WEN).
• Research is needed to establish the relevance of these relationships in a practical feeding situation.
   

Acknowledgements

The financial support for this study was provided by the MEKARN programme of sida-SAREC. The author would like to thank the Agriculture and Natural Resources Department of An Giang University, Long Xuyen City, Vietnam for making available the facilities for this study. The author also would like to thank Dr Preston and colleagues for advice and guidance.

References

AOAC 1990 Official methods of analysis. Association of Official Analytical Chemists, Arlington, Virginia, 15^th edition, 1298 pp.

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 29, 2003, from http://www.cipav.org.co/lrrd/lrrd15/8/chha158.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

Oboe 1980

McDonald Animal nutrition, fifth Edition

Ravindran V and Ravindran G 1988 Changes in the nutritional composition of cassava (Manihot esculenta Crantz) leaves during maturity. Food Chemistry (27): 299-309 

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