Abstract: Availability of roughage constituents to the rumen microbes and supplying adequate nutrients intensely depends on their fibrous properties. Manipulation of these potentially feedstuffs are the great challenges to the nutritionists. Biological upgrading of crop residues is one of the approaches to enhance the release of plant nutrients in the rumen environment by the microbes. Effectiveness of Pleurotus florida on gas production properties of untreated and fungal treated Wheat Stubble (WS) and Date Palm Leaf (DPL) at 2, 4, 6, 8, 12, 24, 48, 72 and 96 h was investigated. Cumulative gas production from untreated WS was significantly higher than treated WS. This effect was not observed in DPL. Total gas productions, irrespective of substrate, in control, mycelial and harvesting stages were significantly different (35.83, 29.50 and 27.45 mL, respectively). Potential gas production was not affected by fungal treatment; however, it was significantly lower in DPL than in WS. Rate of gas production (c) significantly decreased at harvesting stage compare to the control in both substrates. In addition, "c" was higher in WS than in DPL. Predictive Effective Degradability (ED) of WS at different outflow rates was significantly higher than those observed for DPL. As a result of this experiment, it can be concluded that Pleurotus florida treatments of both WS and DPL resulted in no improvement in gas production properties of these 2 roughages.

INTRODUCTION

Ruminants have the capacity to utilize crop residues, which generally have poor nutritional value in terms of their protein and energy. These crop residues are traditionally fed to the animals as the main part of the ration in many of the developing countries However, Dry Matter (DM) intake is not adequate to fulfill the requirements of livestock (Dixon and Egan, 2000). Limitation in DM intake is due to low rate and extent of fermentation of these residues. Date Palm Leaf (DPL) is not fed to animals because of its low palatability and digestibility (Al-Yousef et al., 1994; El-Din and Tag-El-Din, 1996; Bahman et al., 1997). However, these may be overcome by some chemical or biological treatments. During the last decades efforts have been made to improve the nutritive value of poor quality unconventional crop residues but there is no information about fungal treatment of DPL and its comparison with Wheat Stubble (WS). The possibility of biological methods of roughage treatment using white-rot-fungi (Falcon et al., 1995; Jalk et al., 1998) to improve their quality has a great appeal as an alternative to the use of corrosive and pollutant chemicals. However, it should be taken into account that organism grown on the roughage must obtain its energy from the roughage itself (Jung et al., 1992; Miki and Okano, 2005; Safari et al., 2005). Thus the present investigation was undertaken to evaluate in vitro gas production of untreated and fungal treated date palm leaf to that of wheat stubble, a more common roughage used in other countries.

MATERIALS AND METHODS

Wheat stubble and date palm leaf were chopped into 5-7 and 2-3 cm length, respectively. Air-dried 3 kg wheat stubble (harvested manually at ground level) or 6 kg date palm leaf were packed in nylon gunnies (100x120 cm), separately. The gunnies were then soaked in a water pool overnight; thereafter contents were transferred into 45x90 cm plastic bags and pasteurized at 80°C in a boiling pot for 1.5 h (Adamovic et al., 1998; Fazaeli et al., 2003). All the bags were removed from boiling pot, suspended in fermentation houses and left overnight to drain the excess moisture and then cooled.

The pasteurized wheat stubble and date palm leaf were removed from the plastic bags, inoculated with Pleurotus florida spawn at a rate of 3-5% (w/w) and re-packed into plastic bags (Zadrazil et al., 1995; Fazaeli et al., 2002). The bags were immediately tightened with nylon thread and kept in the fermentation house. Each bag contained about 12 kg wheat stubble or 10 kg date palm leaf.

A fermentation house 9x30x3 m was made in order to provide an optimal environment for fermentation and fungal growth. The temperature was maintained at 23±2°C using pad system and fan. The relative humidity was kept at 85±5% using an automatic humidity producer with sufficient aeration and light (Adamovic et al., 1998; Fazaeli et al., 2002). On the third day and after 2 weeks of incubation, bags were crushed on all sides to provide a sufficient aeration necessary for mycelial running and fruiting body formation. Two weeks after spawning (complete mycelial running stage) half of the bags were removed from the fermentation salon and exposed to sun drying. After the third (first stage of fruiting body formation) weeks of incubation, remaining bags were also exposed to sun drying.

The treatments were untreated wheat stubble (UWS), mycelium treated wheat stubble (MWS), fungal treated wheat stubble after harvesting of mushroom (FWS), untreated Date Palm Leaf (UDPL), mycelium treated date palm leaf (MDPL) and fungal treated date palm leaf (FDPL) after harvesting of mushroom.

In each stage, samples were taken from the treatments and dried at low heat oven (60°C), ground to pass through 1mm sieve size and stored in plastic bottle with lid. The samples were subjected to in vitro gas production method at 2, 4, 6, 8, 12, 24, 48, 72, 96 h of incubation period and total gas production (mL/0.5 g substrate) was estimated according to technique reported by Menke et al. (1979). Exponential model (Blümmel and Ørskov, 1993) was chosen to describe the kinetics of gas production from treatments. Rumen liquor was obtained from three ruminally fistulated bulls, maintained on wheat stubble based diet.

The data were subjected to factorial design using two way analysis of variance of SYSTAT software, release 11.0 (Copyright SYATAT Software, Inc., 2004). Differences between means were estimated by Pairwise Multiple Comparison Procedures, Duncan's Method (Cochran and Cox, 1992).

RESULTS

Chemical composition of treated and untreated wheat stubble and date palm leaves are shown in Table 1. Date palm leaves contained significantly higher CP, NDF and ADL and lower ADF than wheat stubble. Fungal treatment also affected chemical composition of the substrates.

The effect of fungal treatment of roughages on total, extent (b) and rate (c) of gas production and lag phase (lag) are presented in Table 2 and graphically illustrated in Fig. 1a and b. There were significant differences between treatments (control, mycelial and harvesting stages) in total gas production during the incubation period. Total gas production in control, mycelial and harvesting stages was 35.83, 29.50 and 27.45 mL, respectively. The volume of gas produced, irrespective of treatments, in wheat stubble (44.56 mL) was higher (p<0.05) than those measured in date palm leaves (17.29 mL). However, the reduction in gas production observed at mycelial and harvesting stages compared with those from control in wheat stubble was not observed in date palm leaves.

Table 1:	Chemical composition of treated and untreated wheat stubble and date palm leaves
a,b,c,d,evalues bearing different superscripts in a column differ significantly p<0.05. Natural = substrate without fungal treatment; NW = Wheat stopple, DPL = Date Palm Leaves

Fig. 1:	In vitro cumulative gas production (mL/0.5 g) at different intervals of treated and untreated date palm leaves (a) and wheat stubble (b)

Table 2:	In vitro total gas production (mL/0.05g) and kinetics of gas production of treated and untreated wheat stubble and date palm leaves
a,b,c,d,evalues bearing different superscripts in a column differ significantly p<0.05. Natural = substrate without fungal treatment; NW = Wheat stopple, DPL = Date Palm Leaves, 1b = Potential gas produced, 2c = Fractional rate gas production (h-1), 3lag = Lag phase (h)

Potential gas production (b) was not significantly affected by treatments, however, it was lower (p<0.05) in DPL (52.15 vs. 29.51). The “b” constant at harvesting stage compared to the control in WS was lower (45.85 vs. 56.85) however, this constant was significantly higher (35.98 vs. 21.90) in DPL at harvesting stage (Table 2).

Rate of gas production decreased (p<0.05) at harvesting stage compare to control in both WS and DPL. In addition to that “c” was higher (p<0.05) in WS than in DPL. Predictive Effective Degradability (ED) calculated at different outflow rates are shown in Table 3. Effective degradability at different outflow rates at mycelial and harvesting stages of WS and DPL were lower than their controls. However, ED of WS at different outflow rates were higher (p<0.05) than those obtained for DPL.

Table 3:	Predicted effective degradability (%) of treated and untreated wheat stubble and date palm leaves
a, b, c,d, evalues bearing different superscripts in a column differ significantly p<0.05. Natural = substrate without fungal treatment; NW = Wheat stopple, DPL = Date Palm Leaves

DISCUSSION

Total gas production was over 60% higher in WS than DPL, which indicated poor fermentability of DPL, evidently due to its higher lignin content (Singh et al., 2005). Additionally, increase in gas production during intervals from WS was higher than those from DPL. It may be a reasonable evidence of the availability of nutrients to microbes during fermentation period and more digestibility of WS in comparison to DPL. This was reflected in both b and c constants which were 43.41 and 53.85% higher in WS compared to DPL, respectively. Effective degradability of WS estimated at 2% outflow rate was 62.46% more than DPL. These results showed a significantly better digestibility of WS compared to DPL, possibly due to lesser accessibility of ruminal microbes to the fiber content of DPL.

Fungal treatment at both mycelial and harvesting stages resulted in 19.18 and 29.68% reduction in total gas production in WS. However, no significant change occurred in the total gas production due to fungal treatment in DPL. Such an interaction between roughages and fungal treatment observed in the present study has also been reported by others (Zadrazil andBrunnert, 1980; Jung et al., 1992; Safari et al., 2005; Okano et al., 2006). Our results of in vitro gas production were not in agreement with Miki andOkano (2005), who reported that fungal treatment of wheat and rice straw increased in vitro gas production by 20 and 11%, respectively. Okano et al. (2006) also reported significant increase in in vitro gas production of bagasse cultured with Lentinula edodes and two strains of Ceriporiopsis subvermispora whereas such alteration was not recorded by Pleurotus eryngii, Pleurotus salmoneostramineus. There is very little report on gas production of either WS or DPL treated with fungi. However, high correlation between the in vitro gas production and DM or OM digestibility has been found (Miki and Okano, 2005; Hozhabri and Singhal, 2006). Variable results have been reported on the effect of white rot fungi on DM digestibility of different low quality roughages depending on the fungi species and substrate (Zadrazil and Brunnert, 1980; Hatakka, 1983; Zadrazil, 1985; Muller and Trosch, 1986; Jung et al., 1992). However, many of reports have demonstrated significant increase in in vitro DM digestibility of roughages (Rouzbehan et al., 2001; Fazaeli et al., 2004: wheat straw; Miki and Okano, 2005: rice and wheat straw; Soilman et al., 2003; Hamza et al., 2003: corn stalks).

CONCLUSION

As a result of this experiment, it can be concluded that Pleurotus florida treatments of both WS and DPL resulted in no improvement in gas production properties of these two roughages.