Nutritional evaluation of crop residues for pigs; pepsin/pancreatin digestibility of seven plant species

J Ly*, Pok Samkol, Chhay Ty 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

Eleven types of tropical crop residues from seven plant species available 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 assessingnutritive value of crop residues for pigs. Leaves and petioles were from banana (Musa acuminata) and sugar cane (Saccharum officinarum)whereas theaerial part was from amaranthus (Amaranthus spp), canavalia (Canavalia ensiformis) and mucuna (Stizolobium deeringianum). Old and new rice (Oryza sativa) straw and cassava (Manihot esculenta) foliage, either in natura, sun-dried or ensiled after 0 or 24 hr of wilting were also evaluated.

The values for DM, N and NDF ranged from 18.8 to 91.9%, 1.30 to 4.97% and 32.3 to 88.7% (in dry basis), respectively. In vitro N digestibility was associated negatively with NDF-linked N (r = - 0.78)and positively with water solubility of N (r = 0.88), DM solubility (r = 0.64) and in vitro DM digestibility (r = 0.61).

It is concluded that the water solubility method is suitable for evaluating tropical fibrous crop residues as feed for pigs and that cell wall linked N is one of the major factors influencing in vitro N digestibility.

Key words:In vitro digestibility, water solubility, plant cell wall, nitrogen, tropical crop residues, pigs

Introduction

There is a considerable amount of information concerning the use of crop residues as feed for ruminants (Greenhalgh 1984; Owen and Aboud 1987; Owen and Jayasuriya 1989), but much less concerning the use of this type of biomass for feeding pigs (Perez 1997). Simple methods such as in sacco rumen degradability (リrskov et al 1980), in vitro gas production (Menke et al 1979; Ly et al 1997) and water solubility of dry matter (Ly and Preston 1997) have facilitated the evaluation of crop residues for ruminants. However, despite the existence of simple in vitro methods for monogastric animals such as in vitro digestibility of N, as determined by pepsin/pancreatin treatment (Dierick et al 1985; Boisen and Fernandez 1995; Pujol et al 2001; Swiech and Buraczewska 2001) and water soluble N (Ly and Preston 2001), there have been fewer attempts to apply them to crop residues.

The aim of the present communication is to report the potential nutritive value of eleven types oftropical crop residues for pigs, by using non-conventional methods of feed evaluation.

Materials and methods

Eleven samples from seven crop residues (Table 1) periodically harvested at the Ecological Farm, at Chamcar Daung, were selected for the study. The samples were sun-dried and ground, except for one sample of cassava leaves which was analysed using fresh material, prior to determining water solubility of DM and N as described by Ly and Preston (2001). In addition, NDF and NDF-N were also determined following the Van Soest et al (1991) and Licitra et al (1996) recommendations, respectively. The ash content of the original samples was determined according to the AOAC (1990) procedures and organic matter was considered to be 100 - % ash. All the analyses were carried out in duplicate.In vitro (pepsin/pancreatin incubation) digestibility of DM and N was assayed in re-ground samples in quadruplicate according to the method described by Dierick et al (1985).

The values for DM, N and NDF in the selected samples (Table 2) were in a wide range (18.8 to 91.9%, and [in dry basis] 1.30 to 4.97% and 32.3 to 88.7%, respectively).

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

Results and discussion

As shown in Table 3, highest in vitro N digestibility values were obtained for fresh cassava leaves (68.0%) and the lowest for leaves from sugar cane (3.7%). Water soluble N followed as similar pattern. Surprisingly, rice straw had values for water solubility and in vitro digestibility of N which were comparable with those of cassava.

There was a close positive correlation (r = 0.88) between water soluble N and in vitro N digestibility (Table 4 and Figure 1). On the other hand, NDF-linked N was negatively associated with water soluble N (r = – 0.79) and in vitro N digestibility (r = - 0.77).

Figure 1: Relationship between water soluble N and in vitro N digestibility
in a range of leaves from crop residues

The water soluble DM estimate was a better predictor (R²= 0.83) of in vitro dry matter digestibility than was the NDF estimate (R²=0.71) (Figures 2 and 3). These findings are in general agreement with those reported for tree leaves and water plants (Ly et al 2001; Ly et al 2002).

Conclusions

The results indicate that:

キ The water solubility method is suitable for evaluating tropical fibrous crop residues as feeds for pigs.

キ Cell wall linked N appears to be one of the major factors influencing the digestibility of the nitrogenous fraction.

Acknowledgments

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

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Received 19 October 2001

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