Background

Agriculture by-products are considered a great potential value for utilization by ruminants as well as rabbits. They represent the maintenance and part of the production requirements (Cheeke 1987). However, in developing countries, as well as in Egypt, animals suffer from shortage of feeds that are continuously increasing in costs.

There is a considerable variation in quantities and qualities of by-products between crops, influenced by species, varieties, climate, season, region, and stage at harvest. The most important parts of roughage are the aerial parts (stems and leaves). These can be utilized as fresh or dry and cut or grazed in the field or in the stable/barn (Chahal 1985).

In Egypt, there are about 25 million tons of plant by-products produced annually. However, wheat straw, rice straw and corn stalks are already being fully utilized by many farmers, either for bedding poultry farms or feeding livestock (Ministry of Agriculture and Land Reclamation 2008). Moreover, Shoukry (2013) recorded that annually, the amount of agricultural residues available in Egypt is about 25.6 million tons, 15.3 million tons of which were crop residues and about 10.3 million tons were agro-industrial by-products. Meanwhile, Sadek (2013) reported that agriculture by-products reached 35 million tons annually, 23 million tons of which were plant wastes (7 million tons of them are used as fodders, 4 million tons were used as organic fertilizers, and the rest of wastes (12 million tons) were left without any use). Furthermore, Ali et al. (1987), Abou Akkada (1988), and El-Shinnawy (1990) estimated the quantities of rice straw (2.5 million tons); meanwhile, corn stalks ranged from 3.3 to 3.5 million tons.

Such roughages are usually high in lignocelluloses and low in available energy; also they are generally low in readily available carbohydrates as well as nitrogen and certain minerals. Their utilization is limited by the low voluntary intake of the animals and by their high transport cost, being bulky (Rissanen et al. 1981 and Abedo 2011).

Low-quality roughage includes enormous amount of cereal crop residues such as rice straw, wheat straw, bean straw, maize stover, corn cobs, and rice hulls. These by-products are all characterized by their high fiber, lignin, cellulose, and hemicellulose contents (Goering and Van Soest 1970).

Also, most cereal wastes are characterized by low crude protein, low available energy, and deficiency in certain minerals. These low-quality roughages are inefficiently utilized by ruminants. This is due to low digestibility and poor nutritive value associated particularly with cereal straw. Their utilization is also limited because of low voluntary intake of the animals and their huge bulk, which makes transportation more expensive. These materials supply no more energy than poor quality hay; their total digestible nutrients (TDN) are less than 50%, and starch value is less than 29% (Balch 1976).

Chahal (1985) noted that the chemical composition of field crop residues contains about 30–40% cellulose, 16–27 % hemicelluloses, and 3–13 % lignin.

Regarding the world feed shortage, a great deal of research works was directed not only to make full use of the roughages but also to increase their feeding value. The intake and utilization of low-quality roughages could be increased by proper supplementation or by various pretreatments. Such methods may involve physical, chemical, and microbial treatments and improve digestibility and nutritive values of field crop residues and wastes (Rangnekar et al. 1982 and Cheeke 1987).

In general, biological treatments were shown to be the most effective way to improve the chemical composition of rice straw or corn stalks (Kiran Singh 1991; Krishna Moorthy et al. 1996; Rangaswami and Bagyaraj 1996; Mahrous and Abou Ammou 2005; Abd-Allah 2007; Abo-Eid et al. 2007; Abd El-Galil 2008).

So, this work was carried out to investigate the impact of feeding the biologically treated or untreated rice straw and corn stalks using Pleurotus ostreatus or Trichoderma reesei at different levels (0, 33, 66, and 100%) on growth performance and economic efficiency of growing NZW rabbits.

Methods

The present study was carried out at El-Nubaria Experimental and Production Station, Rabbit Research Unit, El-Imam Malik Village, National Research Centre.

This work aimed to investigate the possible ways of utilizing rice straw or corn stalks in rabbit feeding. The field work is designed to study the effect of biological treatment by Pleurotus ostreatus cultivated on rice straw and Trichoderma reesei cultivated on corn stalks and replacing clover hay by rice straw and corn stalks at levels (0, 33, 66, and 100%) either with or without microbes adding.

Seventy-eight immature apparently healthy NZW rabbits aged 4–5 weeks (565 ± 13.57 g) were randomly divided into 13 equal experimental groups (6 rabbit in each treatment).

Weaned rabbits were housed in galvanized wire cages (50 × 50 × 45 cm) and provided with stainless steel nipples for drinking, and the feeders allow the recording of feed intake during the feeding trial that continue 13 weeks (91 days).

All experimental groups were kept under the same managerial conditions, and rations were offered pelleted with diameter 4 mm.

Live weight of rabbits was individually recorded weekly, and average daily gain was calculated. Also, feed intake was also recorded weekly throughout the 13 weeks of feeding trial. Feed conversion expressed as g dry matter intake/g gain was calculated.

Biological treatments

Microorganisms

Pleurotus ostreatus and Trichoderma reesei were obtained from the Agriculture Microbiology Department, National Research Centre, Egypt.

Preparation of fungal inoculums

Three-day-old slant cultures of Pleurotus ostreatus or Trichoderma reesei were crushed into flasks containing 20 ml of sterilized water. The fungi spore suspensions were used as inoculums at 10% v/w to inoculate 500 ml capacity flasks containing 25 g of ground waste moistened at solid:liquid ratio of 1:2 with basal medium composed by g/L, 40 sugar cane molasses, 2.0 urea, 0.2 potassium dihydrogen phosphate, and 0.3 magnesium sulfate; the inoculated flasks were incubated at 30 °C for 72 hrs under static solid-state fermentation system.

Preparation of fungal biological treatments

The above prepared inoculate was employed to inoculate 500 g of crop residues under study moistened by the above basal medium at solid:liquid (1:2) at 10% v/w and packed in polyethylene bags (50 × 100 cm). The inoculated bags were incubated under static conditions for 10 days at 30 ± 2 °C; at the end of incubation period, the bags were opened and oven dried at 70 °C till constant weight and the residues are milled for chemical analysis purpose.

Preparation of substrate

A total of 25.00 g of the dried milled substrate were weighed and transferred into a dry clean sterile bottle (120 ml capacity); then 70 ml distilled water were added. Each bottle was immediately coerced with aluminum foil and sterilized in the autoclave at 121 °C for 15 min. The treatments were run in triplicates.

Inoculation

Each bottle was inoculated at the center of the substrate with 2 mycelia disc (10 mm diameter) and covered immediately. They were kept in the dark cupboard in the laboratory at 30 °C and 100% relative humidity (RH). After 21 days of inoculation, the experimental bottles were harvested by autoclaving again to terminate the mycelia growth. Samples of the biodegraded samples were oven dried to constant weight for chemical analysis.

Biological treatments of crop residues under study in large scale

A heap of 160 kg of each tested chopped and crushed rice straw or corn stalks were moistened with medium containing 2.5% molasses, 2.5% urea, 1.5% ammonium sulfate, 1.00% supper phosphate, and 0.5% magnesium sulfate at solid:liquid (1:2). About 80 kg of each crop residues were used with the mixture of fermented fungal biomass and mixed well in mineral medium container and spread and mixed well on a plastic sheet which contained the crop residues. The treated crop residues were shuffled up and downside daily for the prop inoculation period (14 days). At the end of fermentation period, the treated crop residues were collected and exposed to sun-dry until the moisture content reached > 10% and then packed and stored until used in manufacturing the pelleted feed (Fadel et al., 1992).

Manufacturing the pelleted feed

The air-dried compost have been transported to the forage manufacture for making the experimental pelleted feed by substituting clover hay with biologically treated and untreated rice straw or corn stalks at the levels of 33, 66, and 100%.

Animals and feeds

A total number of 78 weaned NZW rabbits were randomly divided into 13 experimental groups of 6 rabbits each. Each group is divided into three replicates of two rabbits each.

All the experimental diets were formulated to be approximately iso-nitrogenous and isocaloric that meet requirements of growing rabbits according to NRC (1977) recommendation.

The ingredients used in diet formulation were shown in Table 1. Meanwhile, the composition and chemical analysis of the experimental diets were presented in Tables 2 and 3.

Table 1 Chemical analysis of different roughages used in ration formulations
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Table 2 Composition of the experimental rations
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Table 3 Chemical analysis of the experimental rations
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The first rations contained 33% clover hay (CH) from the total diet formulation, and it is considered as the control. Rations from 2 to 7 had replaced CH by rice straw without and with Pleurotus ostreatus, and rations from 8 to 13 had replaced CH by corn stalks without and with Trichoderma reesei.

All animals were kept under the same managerial and hygienic conditions. Each replicate which involved two rabbits was housed separately in metal cages and provided with feed and water ad libitum. Ambient temperature at 27–28 °C was achieved with natural light and good ventilation.

Chemical analysis of CH; rice straw (raw, untreated, or treated with Pleurotus ostreatus), corn stalks (raw, untreated or treated with Trichoderma reesei), and the experimental diets was determined according to AOAC (2005) methods.

Economic efficiency

Economic efficiency of the experimental rations for body weight gain and the cost of feed required for producing 1 kg of body weight gain were calculated. The costs of experimental diets were calculated according to the price prevailing at local market as well as the price of tested materials (rice straw and corn stalks) at the time of experiment.

Total feed cost = average feed consumption kg × price per 1-kg feed

Cost feed per kg gain = total feed cost / weight gain

Total revenue = weight gain × price per kg live body weight

Net revenue = price of weight gain − total feed cost

Economic efficiency = net revenue / total feed cost

Analytical procedures

Chemical analysis of ingredients and the experimental rations were analyzed according to AOAC (2005). NDF, ADF, and ADL were determined according to Goering and Van Soest (1970) and Van Soest et al. (1991). Hemicellulose and cellulose contents were calculated by difference using the following equations:

Hemicellulose = NDF−ADF

Cellulose = ADF−ADL

Statistical analysis

Data collected were statistically analyzed as three factors factorial analysis of variance using the general linear model procedure of SPSS (2008).

Meanwhile, Duncan’s Multiple Range Test was used to examine the significance between means (Duncan (1955)).

The following model was used as the following:

$$ {\mathbf{Y}}_{\mathbf{i}\mathbf{j}\mathbf{k}\mathbf{l}}=\boldsymbol{\upmu} +{\mathbf{T}}_{\mathbf{i}}+{\mathbf{S}}_{\mathbf{j}}+{\mathbf{L}}_{\mathbf{k}}+{\left(\mathbf{TS}\right)}_{\mathbf{i}\mathbf{j}}+{\left(\mathbf{TL}\right)}_{\mathbf{i}\mathbf{k}}+{\left(\mathbf{SL}\right)}_{\mathbf{j}\mathbf{k}}+{\left(\mathbf{TS}\mathbf{L}\right)}_{\mathbf{i}\mathbf{j}\mathbf{k}}+{\mathbf{e}}_{\mathbf{i}\mathbf{j}\mathbf{k}\mathbf{l}} $$

where Yijkl = observation

μ = the overall mean

Ti = the effect of treatment (T) for i = 1 to 2, 1 = untreated (without Pleurotus ostreatus or Trichoderma reesei and 2 = treated biologically (treated with Pleurotus ostreatus or Trichoderma reesi)

Sj = the effect of roughage source (S) for j = 1 to 2, 1 = rice straw and 2 = corn stalks

Lk = the effect of level of supplementation (L) for k = 1 to 4, 1 = control diet containing 33% clover hay (0% replacement) 2 = replaced 33% of clover hay by rice straw or corn stalks, 3 = replaced 66% of clover hay by rice straw or corn stalks, and 4 = complete replacement (100%) of clover hay by rice straw or corn stalks

(TS)ij = the interaction between treatment (T) and roughage sources (S)

(TL)ik = the interaction between treatment (T) and replacement levels (L)

(SL)jk = the interaction between roughage sources (S) and replacement levels (L)

(TSL)ijk = the interaction between treatment (T); roughage source (S) and replacement levels (L)

eijkl = the experimental error

Results

Chemical analysis of different ingredients

Data presented in Table 1 cleared that untreated rice straw or biologically treated with Pleurotus ostreatus showed an increase in their contents of crude protein (178.75 and 224.5%), NFE (6.30 and 24.53.5%), and ash (22.73 and 44.45%) compared to the raw rice straw. On the other hand, CF content is reduced by 31.32 and 56.75%; meanwhile OM content decreased by 2.81 and 5.51%, respectively.

Biological treatment with Trichoderma reesei realized a decrease in OM, CF, NDF, and ADF and increased CP and ash contents in corn stalks (Table 1).

Composition and chemical analysis of the experimental rations

Data presented in Tables 2 and 3 mentioned that all tested diets were formulated to cover the rabbit’s requirements according to NRC (1977). Different experimental diets were approximately iso-nitrogenous and isocaloric. The corresponding values of crude protein (CP) ranged from 16.57 to 18.11%, crude fiber (CF) 8.58 to 14.07%, ether extract (EE) 2.15 to 2.57%, nitrogen free extract (NFE) 40.65 to 59.01%, digestible energy (DE) 2412 to 2595 kcal/kg feed, neutral detergent fiber (NDF) 24.02 to 37.97%, acid detergent fiber (ADF) 13.32 to 18.17%, acid detergent lignin (ADL) 2.81 to 12.89%, hemicellulose 10.07 to 20.43%, and cellulose 2.36 to 11.74%, among the different tested diets.

Growth performance

Effect of biological treatments

Biological treatments with fungi significantly (P < 0.05) increased the final body weight (FW), total body weight gain (TBWG), and ADG. In addition, the feed conversion expressed as g DMI/g gain was also significantly (P < 0.05) improved in comparison to rabbits that received rations without fungi (Table 4). Meanwhile, DMI was not affected.

Table 4 Main effect of biological treatments, roughage sources and replacement levels on growth performance of the experimental groups
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Effect of roughage sources

TBWG and ADG significantly (P < 0.05) improved rabbits fed diets containing RS comparing to that fed CS; however, FW was nonsignificantly increased with rabbits fed rations containing RS in comparison with those fed rations containing CS. Also, feed conversion was improved (P < 0.05) when rabbits fed diets containing RS compared to that fed CS. On the other hand, rabbits that received diets containing RS had nonsignificantly decreased the DMI compared to that fed diets containing CS (Table 4).

Effect of replacement levels

Data in Table 4 reported that rabbits fed diets replaced CH in control diet with 33 or 66% of RS or CS significantly increased their FW, TBWG, and ADG compared to the the control and that replaced 100% of both RS and CS containing diets; however rabbits that offered diets replaced 100% of CH by RS or CS caused a significant decrease in their TBWG and ADG compared to the control. Levels of replacing had no significant effect on their DMI. The highest improvement in feed conversion was recorded with rabbits that received diets replaced 33% of CH by RS or CS, followed by that replaced 66% of CH by RS or CS.

Effect of interactions between biological treatments, roughage source, and replacement levels (T × S × L)

There were significantly interaction between biological treatments (T), roughage sources (S), and replacement levels (L) (T × S × L) only for TBWG and ADG. The best TBWG and ADG were recorded for rabbits fed diets replaced 33% of CH by CS that treated with Trichoderma reesei (1939 g and 21.31 g), respectively.

The best fed conversion was realized by rabbits fed diet replaced CH at 33% with RS treated by Pleurotus ostreatus (4.05 g DMI/g gain) as shown in Tables 5 and 6.

Table 5 Effect of interactions between biological treatments, roughage source and replacement levels (T × S × L) on nutrient growth performance of the experimental groups
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Table 6 ANOVA results of biological treatments, roughage sources, and replacement levels on growth performance of the experimental groups
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Economic evaluation

The profitability of using rice straw or corn stalks as a nonconventional cheap feed stuff in growing rabbit diets depends on the price of these by-products and its effect on growth performance.

Data presented in Table 7 illustrated that the lowest cost price/kg feed (2.136 LE) was recorded with rabbits fed 100% corn stalks group that is biologically treated with Trichoderma reesei followed by those fed 100% corn stalks without Trichoderma reesei (2.195 LE) than rabbits group fed diets contained 100% of RS without Pleurotus ostreatus (2.216 LE).

Table 7 Economic efficiency of the experimental groups
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Results obtained also indicated that group rabbits fed 33% biologically treated RS with Pleurotus ostreatus showed the highest economic efficiency (179%) followed by rabbits received 33% for both RS without Pleurotus ostreatus and rabbits received CS biologically treated with Trichoderma reesei (161%). Meanwhile, the lowest value of economic efficiency is recorded by rabbits fed diet contained 100% CS without Trichoderma reesei (75.80%) followed by rabbits offered diet contained 100% treated RS without Pleurotus ostreatus (88.00%).

Discussion

Data published in Table 1 was in agreement with those found by Shoukry et al. (1985) who noted that fungal treatment improves the nutritive value of bagasse because mycelia of all fungi had high cellulose enzyme content which converts cellulosic material into single cell protein or microbial protein and decreased OM after incubation with fungi. Also, our results are in agreement with those obtained by Warren (1996) who reported that the microorganisms are efficient degraders of starch and polysaccharides in plant cell walls as carbon and energy reserves in plant because they have the systems for the hydrolysis of polysaccharides to metabolizable products. Moreover, present results are in the range of results obtained by Abd El-Hakim et al. (2006) who showed that biological treatments of RS increased its CP content and decreased CF content compared to untreated one.

Biological treatment of RS caused decrease in NDF, ADF, ADL, and hemicellulose contents in comparison with either raw or treated RS. Data concerning with cell wall constituents of RS are in harmony with those recorded by Bassuny et al. (2005) and Al Barakel et al. (2007). Also, Fazaeli et al. (2004) observed that fungal treatments (five species of Pleurotus fungi, coded P-21, P-30, P-41, P-60, and P-90) significantly increased CP and decreased NDF and ADF contents of wheat straw. However, culture P-21 significantly showed lower ability than others to degrade the NDF and ADF contents. Furthermore, Mahrous and Abou Ammou (2005) found that biological treatments of RS with P. funiculosum or S. cerevisiae or both increased CP and ash and decreased DM, OM, CF, NDF, ADF, ADL, cellulose, and hemicellulose contents compared with the untreated rice straw.

OM, CF, NDF, ADF, CP, and ash contents in CS are in the same trend with those recorded by Israilides et al. (1994) who observed that fermentation of sugar beet pulp with semisolid substrate increased CP content by 9.9% while ash and lignin contents were found to be similar with those of untreated sugar beet pulp. However, Abd EL-Hakim et al. (2006) showed that biological treatments increased CP content and decreased CF content, compared to untreated one. Abou Ammou et al. (2008) and Al-Asfour (2009) found that when sugar beet pulp and wheat straw are treated with Trichoderma reesei, the OM, CF, NDF, and ADF contents were decreased and CP and ash content were increased.

On the other hand, NFE content of corn stalks as shown in Table 1 was decreased as a result of treatment without or with Trichoderma reesei by 11.95 and 3.82% compared to raw CS.

Reduction in NFE of treatment without or with Trichoderma reesei could be related to the consumption of these carbohydrates by microorganism as energy source for their growth and multiplications. These results are in agreement with those reported by Martin (1977) who noted that many bacterial genera are capable to utilize steroids as a sole carbon and energy source, thereby degrading steroids completely to carbon dioxide and water.

Variations in chemical analysis of the experimental diets (Tables 2 and 3) may be related to the difference of ingredients used in tested ration formulations and that in harmony with those reported by NRC (1977) and in the range that is obtained by Chahal (1985) who reported that chemical composition of field crop residues contains about 30–40 % cellulose, 16–27 % hemicelluloses, and 3–13 % lignin.

Our results (Table 4) are in agreement with those found by Amber et al. (2004) and Ahmed (2005) who noted that live body weight was improved significantly by addition of Opti-Zyme to ration containing corn stover which replaced 50% of clover hay (CH) of the control rabbit rations. This improvement may be related to the beneficial effects caused by biological treatment and micro flora (fungi) helping animals to digest the diets containing non-digestible components like roughage and increase the digestion coefficient by this microorganism and influence the growth and function of the gastrointestinal organs. However, Abd El-Hakim et al. (2006) found that rabbits fed diet containing 35% of CH recorded the highest FW and TWG (P < 0.05) compared to the other groups. In addition, similar results are found by Abd El-Samee (1995) who observed that feed conversion was improved in young rabbits that consumed diet treated with different probiotics in summer period (3.9–4.1 vs. 4.3). Also, Ahmed (2005) found that rabbits fed both additives (bokashi and Opti-Zyme) showed the best feed conversion value, compared to the control group. Thayalim and Samarasinghe (2002) found that addition of effective microorganism to rabbit diet improved feed conversion. Also our results are in agreement with those of Amber et al. (2004) who noticed that rabbits fed on 5 or 10% RS treated with T. reesei significantly (P < 0.05) increased the final weight. Tuikov et al. (1980) found that addition of lactic acid bacteria in calve feeding improved its growth performance. In addition, these results are in agreement with Huang et al. (1990) who reported that body weight of rabbits increased with addition of Trichoderma cellulolytic enzyme for diets containing rice straw. On the other hand, Bonanno et al. (1999) found that adding probiotic to rabbit ration decreased feed intake. El-Badawi et al. (2007) reported that feed intake was not affected when incorporated with treated sugar beet pulp (TSBP) in diet while was significantly (P < 0.05) decreased when incorporated with untreated sugar beet pulp (USBP); this results due to high absorbing capacity (870 ml water/100 g) and swelling capacity (380% of SBP), causing reducing rate of feed passage (Cheeke, 1987). Ahmed (1998) observed that feeding rabbits on 5 or 10% RS treated with fungi T. reesei significantly (P < 0.05) increased daily weight gain. Also, Hicks et al. (1986) observed that adding Lactobacillus acidophilus and Lactobacillus planetarium of cattle ration increased weight gain. Abd-Allah (2007) showed that inclusion of corn cobs treated with T. viride and Saccharomyces cerevisiae at the rate of 20 and 30% of CFM in lamb rations significantly increased ADG. El-Badawi et al. (2007) reported that ADG was significantly (P < 0.05) higher for rabbits fed 25 and 50% TSBP diets (25.99 and 23.99) than those fed control 25 and 50% USBP diets (21.50, 21.04, and 17.00 g/day, respectively). Feed efficiency values were significantly (P < 0.05) higher (4.55 and 4.63) for rabbits fed 25 and 50% TSBP than (5.33, 4.86, and 5.30 kg feed/kg gain) rabbits fed control, 25 and 50% USBP, respectively. Growth performance index (PI) recorded the highest value (70.84) for rabbits fed 25% TSBP compared with 65.80, 52.94, 56.99, and 45.53% for rabbits fed 50%TSBP and control 25 and 50% USBP, respectively. Increase of weight gain and feed efficiency for rabbits fed diets containing TSBP may be due to containing TSBP high content of exogenous enzymes, amino acids, and other secondary metabolites, like vitamins as a result of microorganism activity. Chen et al. (1987) indicated that using T. viride as feed additive in rabbit rations increased weight gain. Besides, Ahmed (2003) reported that replacement 50% of berseem hay by chemically treated CS with urea and biologically treated with T. viride, Cellulomonas cellulans, and Saccharomyces cerevisiae in sheep rations increased ADG compared with control diet. Also, Khalel et al. (2008) showed that there was significant increase in ADG when lambs fed ration contained 10% jojoba meal treated with T. reesei compared with those fed control ration contained untreated jojoba meal. Gippert et al. (1996) showed that ADG was improved when adding probiotic in rabbit ration. Also, El-Badawi et al. (2007) reported that feed efficiency values were significantly (P < 0.05) higher (4.55 and 4.63) for rabbits fed 25 and 50% fungal treated sugar beet pulp than (5.33, 4.86, and 5.30 kg feed/kg gain) rabbits fed control and 25 and 50% untreated sugar beet pulp, respectively. Feed efficiency for rabbits fed diets containing TSBP may be due to high content of exogenous enzymes, amino acids, and other secondary metabolites, like vitamins as a result of microorganism activity. Generally, the obtained results of economic efficiency indicated higher values with RS diets in comparison with corn stalks diets in both treatments.

Our results concerning with economic evaluation are in agreement with those found by Abd El-Hakim et al. (2006) who noted that the highest value of relative economic efficiency was recorded for biologically treated RS with bacteria and fungi (30% replacement CH) compared to control (35% clover hay). Therefore, partial or complete substitution of CH in rabbit rations with such agriculture wastes may be useful in Egypt as a tool for least cost ration formulae in rabbit production. Also, results obtained mentioned that the group of rabbits that received diet replaced 33% of CH by RS and CS realized the highest economic efficiency values compared with the other diets. These results are in agreement with those obtained by Bassuny et al. (2005) and Abd El-Hakim et al. (2006).

Conclusion

Under conditions as that available throughout carrying this work and from the results obtained, it can be concluded that biological treatments of rice straw by Pleurotus ostreatus or corn stalks by Trichoderma reesei were safe, realizing an improvement in their chemical analysis and improved both daily gain and feed conversion, decreasing the costing of diet formulation and therefore decreasing the price of 1-kg live body weight.