Contribution of both soluble and insoluble fractions of desert by-products to their in vitro fermentation

R Arhab*,**, M Aggoun*, H Bousseboua* and D Macheboeuf**

*Laboratoire de Génie Microbiologique et Applications, Département des Sciences de la Nature, Faculté des Sciences,
Université Mentouri, Constantine (Algérie)
rarhab@clermont.inra.fr
**Unité de Recherches sur les Herbivores. Département Elevage et Nutrition des Animaux. INRA Theix 63122 St-Genès-Champanelle (France)

Abstract

Agricultural and agro-industrial by-products are of importance in animal production because they do not compete with human food. These feedstuffs can play an important role in providing fodder for ruminants in developing countries. In this context, the objective of this work is to characterise the in vitro fermentation contribution of both soluble and insoluble fractions, and the ruminal activity promoted in sheep (Ouled-Djellal breed) and goat (Arbia breed) by date palm leaves, collected from old palm trees, in comparison with Aristida pungens (local name drinn: arid gramineous plant harvested at maturity stage) and vetch-oat hay using the gas production technique

A higher digestive capacity has been found in goat in comparison with sheep. For both animal species, the three substrates showed significant (P<0.05) differences concerning 96 h in vitro gas production and rate of gas production. All washed samples showed losses of soluble material. In general, date palm leaves had the greatest washing loss and vetch-oat hay the lowest. The gas production was, in general, significantly (P<0.05) higher for the unwashed substrates. Vetch-oat hay gave the highest values of gas production, Aristida pungens and date palm leaves the lowest. Furthermore, the gas production of the insoluble fraction of vetch-oat hay was higher than that of the other forages. It seems that the fermentation of date palm leaves insoluble fraction (washed substrate) is more degradable than the unwashed ones. This indicates that this feedstuff contains some rumen microflora antagonistic substances which are removed by washing. The rate degradation of the three washed samples is lower than its unwashed ones. The fermentation of these forages requires a more elevated latency phase. These results indicate that the washing of date palm leaves improves their in vitro fermentation by the ruminal microflora. This situation can be due to the dissolution of the anti-microbial factors during washing procedure. In this fact, date palm leaves could be used as an alternative in ruminant rations in the arid zones taking into account the ruminal microflora antagonistic factors.

Keywords: goat, in vitro fermentation, rumen microflora, sheep, washing loss

Introduction

Agricultural and agro-industrial by-products are of importance in animal production because they do not compete with human food. These feedstuffs can play an important role in providing fodder for ruminants in developing countries. However, their use in ruminant rations depends mainly of ruminal degradation of the different parts of the feedstuffs. The ruminant forages are currently described by three different features; the soluble fraction, insoluble fraction and the rate of degradation (Orskov et al 1988; Orskov 1991). The soluble fraction, commonly named washing loss, represents the water soluble components of the organic matter or the dry matter. It includes the soluble sugars and soluble compounds as polyphenolics liberated during the fermentation process (Ly et al 1997). Besides, these parameters are used for assessing the nutritive value of feeds (Orskov 1991; Ly and Preston 1997). In this context, the aim of this study is to characterize the nutritive value of date palm leaves by studying the contribution of both soluble and insoluble fractions to their in vitro fermentation.
 

Material and methods

Samples and site description

Three forages were used in this study: date palm leaves (whole leaves: rachis plus leaflets), which are a by-product of date palm trees (Phoenix dactylifera L.), Aristida pungens (local name drinn) and vetch-oat hay. Date palm leaves, obtained from old date-palm trees, and Aristida pungens (arid gramineous plant harvested at maturity stage) have been sampled from El-Oued (longitude 6°53' E and latitude 33°20' N) in the South East of Algeria. The area is located at altitude of 67m above sea level and receives a mean annual rainfall of 75mm and mean temperature comprised between 11°C in January and 32.5°C in July. Vetch-oat hay has been collected from ITELV (Technical Institute of Breeding, Ain Mlila, Algeria). Feedstuffs were sun-dried, and then ground through a 1-mm screen.

Procedure for removal of soluble compounds

All forages were analysed in duplicate in three different runs according to the procedure described by Pedraza (1998). Samples of known dry matter content (0.3-0.5g, 1-mm screen) were soaked in 150 mL distilled water at room temperature during 1h and 45min while shaken intermittently. Samples were then filtered through a Whatman No.1 (Ф = 15cm) filter paper and washed with water until approximately 500 mL of filtrate was recovered. The filter paper containing the insoluble residue was dried at 60°C until constant weight. The filter papers were transferred to previously tared plastic bags and sealed. Weighing was carried out after 1h, to calculate the filter paper insoluble residue. The soluble fraction was calculated by difference between initial weight of feedstuff and insoluble residue.

In vitro gas production analysis

In vitro gas production was completed according to the procedure described by Menke and Steingass (1988). Each sample, both original forages and insoluble residues, weighing about 200 mg, were introduced into 60 mL calibrated propylene syringes together with 30 mL rumen liquid media solution on a 1:2 ratio. The buffer solutions used have been described by Menke and Steingass (1988). Syringes were incubated at 39°C in an electrically heated, isothermal oven, equipped with a rotor which runs continuously at 9 rpm (GFL 3033). Triplicate of each sample were assayed. Three blanks (rumen fluid + buffer mixture) were incubated at the same conditions.

Rumen liquor, used as inoculum, was collected before morning feeding from the two sheep and the two goats. The in vitro experiment was carried out separately for sheep and goats. Rumen fluid was pumped with a manually operated vacuum pump and transported into two pre-warmed thermos flasks to the laboratory. Immediately on arrival, the rumen liquor of the two animals of the same species were pooled, strained through four layers of gauze and flushed with CO₂.

Calculations and statistical analysis

The results of gas volume produced in vitro were fitted to the exponential model of Orskov and McDonald (1979) : y = a + b (1 - e^-ct), where y (mL) is the gas production at time t, a (mL) is the amount of gas corresponding to the rapidly degradable fraction, b (mL) is the amount of gas corresponding to the slowly degradable fraction, a+b (mL) is the potential gas production and c (%.h^-1) is the fractional gas production. The estimation of these parameters has been made by the Neway Excel software (Chen 1997).

The statistic analysis (ANOVA) was completed using the GLM procedure of SAS (1990), and the differences between means by Least Significant Differences Method (Snedecor and Cochran 1967).
 

Results and discussion

The results of washing losses in the three forages are illustrated in figure 1.

It can be seen that date palm leaves had the greatest washing loss and vetch-oat hay the lowest. The washing loss values obtained in this experiment are in the range of the dry matter loss recorded by Ly and Preston (1997) and Ly et al (1997) for leaves of tropical trees and shrubs using the bag soaking in water method. The differences between feedstuffs could be due to the individual characteristic of each ones, mainly species and maturity. The presence of more ready water-soluble material and small particles as soil can be responsible for the greatest loss of dry matter in date palm leaves.

As part of the initial characterization of the forages studied, table 1 and figure 2 show their in vitro gas production in goat and sheep respectively. A higher digestive capacity has been found in goat in comparison with sheep.

This result confirmed earlier findings concerning the ability of goat to adapt to a wide range of conditions and their greater digestive capacity than sheep (Molina-Alcaide et al 1997; Aregheore 2000). For both animal species, the three substrates showed significant differences (P<0.05) concerning 96 h in vitro gas production and rate of gas production. It can be seen that the highest cumulative gas production was in vetch-oat hay. Whereas, date palm leaves were lowest. Besides, vetch-oat hay was fermented faster than Aristida pungens, and the fermentation rate of Aristida pungens was higher than that of date palm leaves (P <0.05). The lower fermentation of date palm leaves may indicate the presence of an artefact which reduces the microbial activity.

The in vitro gas production characteristics from both the original forages and its insoluble fractions are presented in fig.3 and table 2.

The gas production was, in general, significantly (P <0.001) higher for the original forages. Vetch-oat hay gave the highest values of gas production, Aristida pungens and date palm leaves the lowest. Furthermore, the gas production of the insoluble fraction of vetch-oat hay was higher than that of the other forages. It seems that the fermentation of date palm leaves insoluble fraction (washed substrate) is more degradable than the unwashed ones. These results indicate that the washing of date palm leaves improves their in vitro fermentation by the ruminal microflora and can suppose that this feedstuff contains some rumen microflora antagonistic substances which are removed by washing. The rate degradation of the three washed samples is lower than its unwashed ones. The fermentation of these forages requires a more elevated latency phase.

Figures 4 and 5 show the in vitro gas from the soluble fractions of the three forages. Vetch-oat hay and date palm leaves have reached the greatest values while the Aristida pungens has the lowest. The low contribution from the soluble fraction of Aristida pungens can be due to the fibrous nature of this forage (arid forage). Other factor that can contribute to the low gas production in this soluble fraction could be the presence of soluble but not digestible material. However, the greater ruminal degradation, observed for the soluble and insoluble fractions of date palm leaves comparatively to the original forage, let expected the presence of anti-nutritional factors which are dissolved in water.

Conclusion

• This study reveals that the washing procedure improves the in vitro gas production of date palm leaves. Such data suggest that the washing method may indicate the presence of anti-microbial factors which are dissolved during the treatment. Furthermore, this method can be used for assessing the contribution of the different fractions of forages to their nutritive value.
   

References

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Received 21 December 2006; Accepted 6 July 2007; Published 3 August 2007

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