Nutritional evaluation of tropical leaves for pigs: Pepsin/pancreatin digestibility of thirteen plant species

J Ly*, Pok Samkol and T R Preston 

University of Tropical Agriculture Foundation, 
Royal University of Agriculture, Chamcar Daung near Phnom Penh, Cambodia
 samkol@uta.edu.kh       trpreston@email.com
^*Visiting scientist at the UTA Foundation
Present address: Swine Research Institute, Punta Brava near Havana City, Cuba
jlyca@yahoo.com

Abstract

Thirteen types of tropical trees and shrubs available in the ecological farm of UTA, at Chamcar Daung, Cambodia, were selected for a screening test to evaluate in vitro pepsin/pancreatin digestibility of N and to explore the possible interdependence with other non conventional tests for assessing nutritive value of foliages for pigs. Leaves and petioles were from Acacia auriculiformis, Artocarpus heterophyllus, Borassus flabellifer, Cocos nucifera, Desmanthus virgatus, Eucalyptus spp, Flemingia macrophylla, Gliricidia sepium, Hibiscus rosasinensis, Leucaena leucocephala, Moringa oleifera, Morus alba and Trichanthera gigantea. DM, N and NDF range of value were 21.0 to 60.9%, 1.27 to 4.13% and 24.1 to 73.0% in dry basis respectively. 

It was found that an increase in pepsin/pancreatin, in vitro N digestibility was associated with less NDF-linked N (R² 0.50; P<0.007) and lower dry matter content (R² 0.58; P<0.002) in leaves, and higher values of DM solubility (R² 0.67; P<0.001), in vitro DM digestibility (R² 0.76; P<0.001) and N water solubility (R²  0.82; P<0.001). Highest in vitro N digestibility coefficients were obtained for Moringa oleifera (79.2%), Hibiscus rosasinensis (74.2%), Gliricidia sepium (69.4%) and Morus alba (47.9%). The lowest in vitro N digestibility was observed for palmaceae (Cocos nucifera, 9.4% and Borassus flabellifer, 5.1%).

 It is suggested that simple, cheap and easy methods can be used for the nutritional evaluation for pigs of leaves of trees and shrubs in the tropical world. It is recommended to continue studying simple methods of estimating the N status of  leaves for pigs and to characterize by this approach other plant species.

 Key words: in vitro digestibility, water soluble, nitrogen, tropical trees and shrubs leaves, pigs

 
Introduction

According to Blair (1989), the trees and shrubs that can be used as fodder encompasses some 74 genus of plants, while Brewbaker (1986) suggested that more than 200 species of trees fix N and are reported to be useful as fodder species.

The use of trees and shrubs leaves as pig feed has received little attention in the tropics, in spite of the fact that major tropical crops have a high energy efficiency as sun-capturing plants. Research with these plants for monogastric animal feeding has mainly been directed to their use as sources of energy, as many of them produce substances which are either devoid of cell wall materials or contain very small amounts (Perez 1977).  Amongst these sources of energy are the juice from sugar cane and the sugar palm (Borassus flabellifer), the oil from the oil palm, and the starch from the roots of cassava. When these energy sources are used as the basis of the diet,  the inclusion of fibrous biomass rich in protein is facilitated, since the amount of cell walls in the overall feed will be similar to that in conventional pig diets based on cereal grains.

Very little is known of the nutritional value of tree and shrub leaves for pigs, especially the protein fraction, and data arising from ruminant nutrition studies are of negligible value since they can not be extrapolated to monogastric animals. Furthermore there is a need to develop rapid and inexpensive methods to assess the nutritive value of foliage feeds for pigs, as a first approach to advancing knowledge about digestive utilization by the animals of leaf nutrients.

In a previous report, it was shown that the water solubility of N was strongly correlated with pepsin/pancreatin, in vitro digestibility of N in several samples of tropical forages (Ly and Preston 2001). The aim of the present communication is to report the potential nutritive value of thirteen tropical tree leaves for pigs, using non-conventional methods of feed evaluation.

Materials and methods

Thirteen tropical trees and shrubs grown in the Ecological Farm, at Chamcar Daung (Table 1), the leaves of several of which are periodically harvested for feed, were selected for the study. Samples of leaves and petioles were separated from stems and either sun-dried and ground, or sub-sampled to determine water solubility of DM and N as described by Ly and Preston (2001). In addition, NDF and NDF-N were also determined following the recommendations and methods of Van Soest et al (1991). The ash content of the original samples was determined according to AOAC (1990) procedures and organic matter percentage was considered to be 100 - % ash. DM was estimated in a microwave oven according to the method described by Undersander et al (1993). All the analyses were carried out in duplicate. 

 There was a wide range of values (Table 2) for the content of DM (21.0 to 60.9%, on fresh basis),  N (1.27 to 4.13%  in DM) and NDF (24.1 to 73.0% in DM). In vitro, pepsin/pancreatin digestibility of DM and N was assayed in re-ground samples in quadruplicate according to the method of Dierick et al (1985). Incubations of leaf sample were conducted in quadruplicate and analytical methods were the same used for determination of the chemical composition. 

Pearson correlation coefficients and other basic statistical approaches were determined by standard biometrical analyses (Steel and Torrie 1980), using the Minitab software (Ryan et al 1985).

Results and discussion 

Gliricidia sepium, Hibiscus rosasinensis, Moringa oleifera and Morus alba had the highest values for DM water solubility (Table 3). Even higher values for water solubility of N (70.0 and 62.2%) were recorded for Moringa oleifera and Gliricida sepium, respectively. Highest values for in vitro N digestibility were obtained for Moringa oleifera (79.2%), Hibiscus rosasinensis (74.2%), Gliricidia sepium (69.4%) and Morus alba (47.9%). The lowest in vitro N digestibility was observed in the palmaceae (Cocos nucifera, 9.4% and Borassus flabellifer, 5.1%). Palm leaves also exhibited low values for DM water solubility and in vitro digestibility of DM.

The analysis of interdependence amongst the different nutritive indices indicated that N content in leaves was not associated with water solubility and in vitro digestibility values (Table 4). On the other hand the cell wall fraction of leaves was positively (P<0.05) associated to NDF linked N, and was inversely related (P<0.05) with water solubility and in vitro digestibility of DM. There was a negative relationship (P<0.05) between the NDF-N fraction and all the solubility indices. 

 In general, an increase in the amount of N contained in the cell wall fraction led to a significant (P<0.05) decrease in N solubility, either in water or in the enzymatic solutions. In this connection, it was found that pepsin/pancreatin, in vitro N digestibility was associated negatively with NDF-linked N (R² 0.50; P<0.007) and dry matter content (R² 0.58; P<0.002), and positively with DM solubility (R² 0.67; P<0.001), in vitro DM digestibility (R² 0.76; P<0.001) and N water solubility (R²  0.82; P<0.001).

The results of the present investigation strongly support previous findings (Ly and Preston 2001) claiming that water soluble N is strongly correlated with in vitro, pepsin/pancreatin digestibility of the N fraction of leaves of tropical trees and shrubs. The present report provides some analytical information about one of the possible causes of the unavailability of N compounds present in leaves from several trees and shrubs. This is of particular importance, since it has been clearly demonstrated that in vitro digestibility of N can predict in vivo, ileal digestibility of N (Dierick et al 1985; Boisen and Fernandez 1995). On the other hand, total tract digestibility data obtained from balance experiments conducted with pigs fed different tree leaves, suggest that a similar, parallel order rank could exist in leaves fed to pigs (Table 5). 

Conclusions

It is suggested that simple, cheap and easy methods can be used for the nutritional evaluation for pigs of leaves of trees and shrubs in the tropics. 

Acknowledgments

This publication is an output from a collaborative research project partially funded by FAO, Rome (certifying officer, Dr Manuel Sanchez, AGAP). The authors are indebted to the laboratory and field staff of the University of Tropical Agriculture Foundation (Chamcar Daung) for technical assistance.

 
References

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 Received 10 October 2001

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