Livestock Research for Rural Development 14 (1) 2002

http://www.cipav.org.co/lrrd/lrrd14/1/ly141a.htm

Nutritional evaluation of aquatic plants for pigs: pepsin/pancreatin digestibility of six 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

Seven samples from six aquatic plant species available in the Ecological Farm of UTA, Chamcar Daung, Cambodia, were selected for a screening test to evaluate in vitro pepsin/pancreatin digestibility of N and to explore the possible relationships with other non conventional tests for assessing their nutritive value for pigs. The samples were the aerial part of water hyacinth (Eichhornia crassipes) and  water spinach  (Ipomoea aquatica), and the entire plants from water lettuce (Pistia stratiotes), azolla (Azolla pinnata), duckweed (Lemna minor) and spirodella (Spirodella polyrhyza). The duckweed was analysed fresh or after sun-drying. 

Dry matter (DM) values were from 6.3 to 91.1%;  nitrogen (N) and neutral detergent fibre (NDF) concentrations (dry basis) were from  2.31 to 5.54 % and 29.7 to  58.1%, respectively.  Water solubility of N and in vitro digestibility of N were high and within a relatively narrow range (N solubility, 59.3 to 81.5%; in vitro, pepsin/pancreatin N digestibility, 50.5 to 76.6%). In vitro N digestibility was positively associated with water soluble N (r=0.74), water soluble DM (r =0.71) and in vitro DM digestibility (r=0.75) but not with NDF-linked N (r = -0.043).  In vitro N digestibility was highest for azolla and fresh duckweed (76.6 and 75.4% respectively) and lowest for water hyacinth (50.5%).  Water soluble DM (r = 0.74) was a better predictor of in vitro DM digestibility than NDF (r = -0.48).

The results of this study show that water soluble N is a useful indicator of the digestibility for pigs of the protein in water plants.

Key words: aquatic plants, in vitro digestibility, nitrogen, pigs, water solubility
 

Introduction

Aquatic plants, either floating macrophytes or amphibious species, are in current use in several tropical countries of Southeast Asia (Perez 1997; Leng 1999). The use of this type of biomass as a supplement for pigs is very common amongst farmers and smallholders in the SE Asia region. The feeding value for pigs of water spinach has received some attention in the Mekong Delta in Vietnam (Le Thi Men 1999); duckweed has been extensively studied in Vietnam (see Leng 1999). A considerable amount of information on water hyacinth is available elsewhere (see for example, Bonomi et al 1981; Mishra et al 1987), and some data on the nutritive value of water hyacinth for pigs in tropical China have been reported by Aumaitre et al (1992).

In contrast with the accumulating experimental evidence from Vietnam on water spinach and duckweed as feed supplements for pigs, very little is known from other Southeast Asian countries and for other aquatic plants (see Perez 1997).  However, several studies on the nutritive value of duckweed, azolla and water hyacinth have been reported in tropical America (Becerra 1990, 1991; Domiguez et al 1996; Dominguez and Ly 1997; Gutierrez et al 2001).

The experiments reported in this communication aimed to assess the nutritive value for pigs of the protein in a range of water plants and to test the relationships between the simple water soluble N method (Ly and Preston 2001; Ly et al 2001a,b)) and the in vitro pepsin-pancreatin N digestibility technique which has been shown to be highly correlated with in vivo ileal digestibility of protein in pigs (Dierick et al 1985).

Materials and methods

Six tropical aquatic plants were selected for the study (Table 1). The samples were obtained from plants that were: harvested periodically at the UTA  Ecological Farm on the campus of the Royal University of Agriculture, Chamcar Daung; were purchased in the local market;  or were collected from a lake close to the University Campus. The samples were the aerial part of water hyacinth (Eichhornia crassipes) and  water spinach  (Ipomoea aquatica), and the entire plant from water lettuce (Pistia stratiotes), azolla (Azolla pinnata), duckweed (Lemna minor) and spirodella (Spirodella polyrhyza). The duckweed was analysed fresh or after sun-drying. Analysis for water solubility of DM and N was as described by Ly and Preston (2001). NDF and NDF-N were determined following the procedures of  Van Soest et al (1991) and Licitra et al (1996), respectively. In vitro pepsin-pancreatin N digestibility was determined according to the method described by (Dierick et al 1985).  The ash content of the original samples was determined according to AOAC (1990). Organic matter was considered to be 100 - % ash. All the analyses were carried out in duplicate. 

Mean values for DM ranged from 6.3 to 91.1%, and for N and NDF (dry basis) from 2.31 to 5.54 % and from 29.7 to 58.1%, respectively (Table 2). The selected materials were characterized by a low DM content, with the exception of the sun-dried  duckweed, and a relatively high concentration of N. The aerial part of water hyacinth was much lower in crude protein (14.0% in DM) than the other water plants (range of 22 to 34% in DM). .

In vitro, pepsin/pancreatin digestibility of DM and N was assayed in dried, re-ground samples in quadruplicate according to the procedure outlined by Dierick et al (1985). Incubations of every leaf sample were conducted in quadruplicate and subsequent analyses were the same as used for determination of the chemical composition of the samples.

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

Results and discussion

In vitro digestibility and water solubility of N was particularly high in the samples of azolla and duckweed, whereas this index was low for water hyacinth (Table 3). Water lettuce and spirodella showed the lowest water solubility of DM, while in vitro digestibility of DM was lowest in water hyacinth. 

The high values for in vitro digestibility and water solubility of N in duckweed and azolla are in accordance with reports from Cuba (Dominguez et al 1997) and Vietnam (Ly and Preston 2001). There was a reasonably close correlation between water soluble N and in vitro N digestibility (r = 0.62; Figure 1) and between water soluble DM and in vitro DM digestibility (r = 0.74; Figure 2). The relationship between NDF and in vitro DM digestibility was low (r = -0.48; Figure 3). Nitrogen linked with the cell wall (NDFN) bore no relationship with in vitro N digestibility (r = -0.043). Introducing in vitro N digestibility of casein (99.7 ± 0.28%,n = 4) in the correlation matrix resulted in highly significant values (P<0.001) for the correlations between in vitro digestibility of N: and water solubility of DM (0.88),  in vitro DM digestibility (0.87) and water solubility of N (0.92). Results from the correlation matrix for the indices examined are listed in Table 4. 

The results of the present investigation show the same trend found in previous studies (Ly and Preston 2001; Ly et al 2001b) where water soluble N was correlated to in vitro, pepsin/pancreatin digestibility of the N fraction of cell wall materials. Studies with conventional feeds for pigs have shown that in vitro digestibility of N can predict in vivo, ileal digestibility of N (Dierick et al 1985; Boisen and Fernandez 1995; Pujol et al 2001; Swiech and Buraczewska 2001). A similar conclusion can be drawn for non-conventional diets of aquatic floating macrophytes (Table 5). 

 

Conclusions

The results of the experiment described in this communication demonstrate that non-conventional evaluations of cell wall rich materials as potential protein sources for pigs are  viable alternative options that can be readily applied in many tropical countries. Further research is needed to improve the accuracy of measurements relating to water solubility and N digestibility of tropical foliage feeds and also to find theoretical support for the present results.
 

Acknowledgments

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

References 

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Received 17 October 2001

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